% % This file was created by the TYPO3 extension % publications % --- Timezone: CEST % Creation date: 2024-03-28 % Creation time: 22:14:26 % --- Number of references % 103 % @Phdthesis { Herdrich:348991, author = {Herdrich, Marc Oliver}, title = {Anwendung kryogener Kalorimeter f\{\"\{u\}\}r hoch aufgel\{\"\{o\}\}ste Pr\{\"\{a\}zisions-R\{\"\{o\}\}ntgenspektroskopie}, year = {2024}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena}, pages = {127 p.}, file_url = {https://repository.gsi.de/record/348991} } @Phdthesis { Salman:349004, author = {Salman, Haydar Sarper}, title = {High-power frequency combs for precision spectroscopy in the extreme ultraviolet}, year = {2024}, school = {Universit\{\"\{a\}t Hamburg}, pages = {101 p.}, file_url = {https://repository.gsi.de/record/349004} } @Phdthesis { Balla:349001, author = {Balla, Prannay}, title = {Nonlinear optics approach towards precision spectroscopy of highly charged ions and nuclei}, abstract = {Spectroscopy of highly charged ions and nuclei is a field with great potential to open new frontiers for precision metrology, act as a scientific test bed for quantum electrodynamics, and contribute to the advancement of technology in applied physics. However, precision spectroscopy of these species typically requires laser sources with high photon energies and narrow line widths in the vacuum ultraviolet (VUV) part of the electromagnetic spectrum. The aim of this dissertation is to develop key methods which will enable to create a VUV laser source tailored to the demands set by this spectroscopy application. Laser pulses with a duration of few optical cycles have a key potential for VUV generation, and therefore for spectroscopy of highly charged ions or nuclei. Furthermore, high average power lasers play a key role in addressing narrow transitions. However, laser sources supporting high average power such as Ytterbium-based laser systems, have a pulse duration of a few hundred femtoseconds. It is therefore essential to compress the pulses to a short duration. In this dissertation, we address temporal pulse compression of such high average power laser sources to few cycles. A well-known demanding objective for VUV spectroscopy is the low energy transition of the Thorium 229 (229Th) nucleus. When this dissertation work started, the energy of this transition was known within a range of 149.7 +/- 3.1 nm. However, a laser with a narrow linewidth, high-power and wavelength tunability covering this range is not yet available. This dissertation addresses the development of a high-power frequency comb laser to support tunable VUV generation to drive the low energy nuclear transition of 229Th. Finally, we discuss a preliminary experiment to investigate the low energy VUV nuclear transition of highly charged 229Th89+ ions. This experiment has the potential to locate the low energy nuclear transition of 229Th at a precision two orders of magnitude higher than the currently known uncertainty range.}, year = {2023}, month = {12}, day = {21}, school = {Universit\{\"\{a\}t Hamburg}, pages = {124 p.}, file_url = {https://repository.gsi.de/record/349001} } @Phdthesis { Baghdasaryan:348992, author = {Baghdasaryan, Baghdasar}, title = {Spatio-spectral engineering of entangled and single photons in parametric down-conversion}, abstract = {Engineered photons from spontaneous parametric down-conversion (SPDC) are a valuable tool for studying and applying photonic entanglement, as well as serving as an effective source of single photons. In SPDC, a nonlinear crystal converts a high-energy photon from a laser field into a photon pair, commonly known as signal and idler. Both the theoretical and experimental research conducted by SPDC has primarily focused on the paraxial regime, where the transverse momentum of photons is referred to as the spatial degree of freedom (DOF), and frequency is considered as the spectral DOF. Hence, this dissertation also considers the paraxial regime. Photon pairs generated through SPDC inherently exhibit spatio-spectral coupling, which implies that photons with different spatial DOFs possess varying spectra. While quantum optics applications often focus on either spatial or spectral DOFs independently, the correlation between them poses a fundamental challenge in protocols involving entangled photon sources or single-mode photon states. Theoretical studies on SPDC, that address both space and spectrum together, are mostly limited to approximate wave functions of photon pairs or involve numerical computations. Such theoretical studies usually consider either monochromatic signal and idler photons (the narrowband approximation), loosely focused pump and collection beams (the plane wave approximation), or infinitesimally thin crystals (the thin crystal approximation). This dissertation aims to bridge the gap between the fundamental theory of SPDC and its practical applications. In particular, we have developed a comprehensive theory that does not rely on a specific pump beam or nonlinear crystal and goes beyond the common narrowband, plane wave, and thin crystal approximations. The developed approach accurately describes the inseparability of spatial and spectral DOF and applies to a wide range of experimental setups. Furthermore, we show that the origin of the spatio-spectral coupling is closely related to the Gouy phase of the interacting beams. We utilize the developed theory, taking into account the spatio-spectral coupling insights, to control the entanglement of photon pairs from SPDC. As an application, we shape the spatial distribution of the pump beam to design an efficient source of high-dimensional entangled states in the spatial DOF. In our second application, we tailor simultaneously the effective nonlinearity of the crystal and spatial distribution of the pump, to engineer single-mode photons.}, year = {2023}, month = {12}, day = {14}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena}, pages = {103 p.}, file_url = {https://repository.gsi.de/record/348992} } @Phdthesis { 976151827026_2023, author = {Wanisch, Darvin}, title = {Dynamics of quantum information in many-body systems with nonlocal interactions}, abstract = {The dynamics of quantum information lies at the heart of future technologies that aim to utilize the laws of quantum mechanics for practical purposes. Beyond that, it provides a unifying language that shines new light on longstanding problems home to historically separate fields of theoretical physics. Considering how quantum information propagates and spreads over the degrees of freedom of a quantum many-body system far from equilibrium has proven particularly helpful for various subjects, ranging from the emergence of statistical mechanics in isolated quantum systems to the black hole information paradox. Crucial for these developments are impressive experimental advances that nowadays allow us to explore the nonequilibrium physics of paradigmatic, simple, and (almost) isolated quantum many-body systems in the laboratory. In this thesis, we investigate the dynamics of quantum information in one-dimensional systems of interacting qubits, i.e., spin-chains, where we particularly consider systems that embody nonlocal interactions. The latter are ubiquitous in many experimental platforms for quantum simulation. Our results reveal an interesting connection between two complementary probes of quantum information dynamics, i.e., entanglement growth and operator spreading. This connection allows us to characterize different dynamical classes and underlines that nonlocal interactions induce rich behavior, such as slow thermalization accompanied by superballistic information propagation. In particular, we show that the famous slowdown of entanglement growth in systems with powerlaw interactions implies a slowdown of operator dynamics. The latter clearly distinguishes a system with powerlaw interactions from a system possessing fast scrambling, a characteristic property of black holes and holographic duals to theories of quantum gravity.}, year = {2023}, month = {9}, day = {26}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00059018} } @Phdthesis { 930197245550_2023, author = {Sundqvist, C.}, title = {Signatures of quantum vacuum nonlinearity in two-beam laser collisions}, abstract = {One of the many astonishing predictions of quantum field theory is the nonlinear nature of the quantum vacuum. In the context of quantum electrodynamics this enables classically forbidden, nonlinear interactions between electromagnetic fields in the vacuum. One much pursued idea to test this prediction is to excite the quantum vacuum with high-intensity laser pulses to emit signal photons that can be distinguished from the driving laser photons, for example, by their polarization or photon energy. A major experimental challenge is the small number of signal photons compared to the background photons. With the aim of identifying a potential discovery experiment of quantum vacuum nonlinearity, we provide theoretically firm predictions for two different quantum vacuum signatures with an emphasize on experimentally feasible setups. This covers on the one side the much studied effect of vacuum birefringence, for which we analyze an innovative setup using a single X-ray free-electron laser. Special attention is paid to the influence of the optical components in the setup on the laser pulse properties. On the other side, we perform an in-depth study of a signature of quantum vacuum nonlinearity that has received less attention so far, namely laser photon merging. The signal photons here have the outstanding property that they differ in photon energy from the background photons and can thus be isolated efficiently. We show that, using state-of-the-art technology, the merging signal can compete with the vacuum birefringence signal in terms of its suitability for a potential discovery experiment of quantum vacuum nonlinearity.}, year = {2023}, month = {8}, day = {29}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00058919} } @Phdthesis { 764370821525_2023, author = {Shi, M.}, title = {High-contrast laser-driven monoenergetic proton beams and near-critical density plasma diagnosis}, abstract = {In this dissertation, the experiments are conducted at the Jenaer Titanium: Sapphire 200 Terawatt Laser System (JETi200) located in Jena, Germany. With its excellent temporal contrast, the few-nanometer freestanding target can remain in a solid state for a few picoseconds before the main pulse arrives, greatly reducing the pre-expansion of the target. The resulting proton beams exhibit distinctive features in terms of cut-off energy and energy spectrum distribution. The proton beams in the presented experiment show a more than 30 MeV monoenergetic peak under the circularly polarized laser, and the highest peak particle kinetic energy per Joule of laser energy is around 20MeV/J. As opposed to the circularly polarized driving light, the cut-off energy shows weak dependence on the target thickness when irradiated with linearly polarized light. Moreover, the implementation of a transmission light diagnostic in the experiment indicates that the transmission light of the main pulse is significantly weaker than that in other similar experiments. The energy and energy spectrum of the protons provide the potential to conduct in vivo research and proton skin therapy using the Terawatt-level laser system. Laser contrast significantly impacts laser-driven ion acceleration, as low contrast can lead to premature expansion of thin targets. The evolution of premature expansion, caused by pre-pulses, is primarily based on numerical calculations research. However, in this paper, I conduct a comprehensive experimental study of pre-pulse-induced pre-plasma evolution, including the measurement of pre-plasma evolution time and comparison with a previous numerical model. This investigation is especially beneficial for the latest generation of laser ion accelerators, as it enables the precise quantification of temporal contrast requirements in the Petawatt laser driver era.}, year = {2023}, month = {7}, day = {20}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00058331} } @Phdthesis { 727814441276_2023, author = {Minneker, Bj\{\"\{o\}\}rn}, title = {Generation of spatio-temporal structured high-order harmonics}, abstract = {Starke Laserfelder sind f\{\"\{u\}\}r die Erforschung der Laser-Atom-Dynamik in der modernen Physik unerl\{\"\{a\}sslich. Die Erzeugung von Harmonischen h\{\"\{o\}\}herer Ordnung (HHG) ist ein bedeutender Starkfeldprozess, bei welchem ein ionisiertes Elektron durch das elektrische Feld des einfallenden Lasers beschleunigt wird und anschlie\{\"\{s\}\}end mit seinem Mutterion rekombiniert. Das beschleunigte Elektron emittiert bei der Rekombination schlussendlich ein Photon, welches auf makroskopischer Ebene h\{\"\{o\}\}herer harmonische Strahlung entspricht. J\{\"\{u\}\}ngste Fortschritte in der Lasertechnologie erm\{\"\{o\}\}glichen die Erzeugung intensiver Laserfelder im mittleren Infrarotbereich. Diese neuen Laserquellen erweitern den Parameterbereich der HHG erheblich bez\{\"\{u\}\}glich des schwach relativistischen Bereichs, in welchem das Magnetfeld des einfallenden Laserfeldes zu diesem Prozess beitr\{\"\{a\}gt. In dieser Dissertation wird ein theoretisches Modell der HHG vorgestellt, welches eine formale Erweiterung der bekannten Starkfeld-N\{\"\{a\}herung auf den schwach relativistischen Bereich darstellt. Generell kann das Modell im Gegensatz zu aktuellen Ans\{\"\{a\}tzen beliebig r\{\"\{a\}umlich strukturierte Lichtfelder ber\{\"\{u\}\}cksichtigen und bietet somit die M\{\"\{o\}\}glichkeit, verdrillte Lichtstrahlen im schwach relativistischen Regime zu untersuchen. Das hier entwickelte Modell betrachtet explizit einen elliptisch polarisierten ebenen Laserstrahl als Beispiel. Dar\{\"\{u\}\}ber hinaus werden auch komplexere Laserfelder betrachtet und anschlie\{\"\{s\}\}end kurz diskutiert. Dar\{\"\{u\}\}ber hinaus wird in dieser Dissertation die Phasenanpassung im Kontext der HHG untersucht, die mit einer geringen Konversionseffizienz von weniger als 0, 1 {\%} behaftet ist. Die Suche nach geeigneten externen Parametern, unter denen die Konversionseffizienz entsprechend hoch ist, ist daher von gro\{\"\{s\}\}em In- teresse f\{\"\{u\}\}r die Starkfeldgemeinde. Es wird ein analytischer Ausdruck f\{\"\{u\}\}r die kritische Intensit\{\"\{a\}t abgeleitet, der die Bedingung der Phasenanpassung f\{\"\{u\}\}r einen beliebigen Satz von Anfangsparametern erf\{\"\{u\}\}llt. Der Ansatz ist auf wasserstoff\{\"\{a\}hnliche Edelgase und linear polarisierte Gau\{\"\{s\}\}-Laserpulse mit beliebigen Laserfeldparametern beschr\{\"\{a\}nkt, die die \{\"\{u\}\}blicherweise verwendeten Konfigurationen umfassen. Der analytische Fehler im Vergleich zu numerischen Berechnungen ist kleiner als 1 {\%}, w\{\"\{a\}hrend die Berechnungszeit um vier bis sechs Gr\{\"\{o\}\}\{\"\{s\}\}enordnungen verbessert wird.}, year = {2023}, month = {7}, day = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00059045} } @Phdthesis { 509211369110_2023, author = {Soguel, R.}, title = {On a vacuum state redefinition in QED corrections to energy shifts of heavy highly charged ions}, abstract = {Every interesting quantity to be investigated in the realm of bound-state quantum electrodynamics (BSQED), such as, for example, the Lamb shift, the (hyper)fine-splitting or the g-factor, is closely or remotely connected to the energy levels of the considered system. Therefore, as a prerequisite, it is mandatory to have the ability to accurately assess energy levels of increasingly sophisticated electronic configurations of atoms or ions. BSQED predictive powers are nowadays limited to either simple light systems, where an αZ expansion is justified, or heavy few-electron highly-charged ions, where specialized all-order methods in αZ are required, to reliably capture interelectronic interactions. The redefined vacuum state approach, which is frequently employed in the many-body perturbation theory, proved to be a powerful tool allowing analytical insights. This thesis elaborates on this approach within BSQED perturbation theory, based on the two-time Green’s function method. In addition to a rather formal formulation, the particular example of a single-particle (electron or hole) excitation with respect to the redefined vacuum state is considered. Starting with simple one-particle Feynman diagrams, characterized by radiative corrections to identical single incoming and single outgoing state, first- and second-order many-electron contributions are derived, namely screened self-energy, screened vacuum-polarization, one-photon-exchange, and two-photon-exchange. The redefined vacuum state approach provides a straightforward and streamlined derivation facilitating its application to any electronic configuration. Moreover, based on the gauge invariance of the one-particle diagrams, various gauge-invariant subsets within analysed many-electron QED contributions are identified. The identification of gauge-invariant subsets in the framework of the proposed approach opens a way to tackle more complex diagrams, where the decomposition into simpler subsets is crucial.}, year = {2023}, month = {7}, day = {4}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00058487} } @Mastersthesis { 843316920176_2023, author = {Over, T.}, title = {Probing the Impulse Approximation via Polarization Studies on Inelastically Scattered Hard X-Rays}, year = {2023}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=613}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 235649989470_2023, author = {Zhang, Y.}, title = {Carrier-envelope phase (CEP)-dependent strong-field ionization at infrared (IR) wavelengths}, abstract = {Intense laser-matter interactions are generally determined by the instantaneous electric field of the laser pulse. For light-matter interactions with few-cycle pulses, the carrier-envelope phase (CEP) plays a critical role as the temporal variation of the electric field depends on the phase. This has a profound impact on many scientific applications. More importantly, controlling the CEP provides an additional degree of freedom to control field-driven processes in atomic, molecular and solid-state systems. In this thesis, we will demonstrate the development and implementation of a single-shot CEP measurement technique, i.e., the so-called carrier-envelope phasemeter based on stereo-above-threshold ionization in Xe and operating at short-wave infrared (SWIR) wavelengths, which allows for simultaneous pulse duration measurement. The experimental results are compared to simulations with two different theoretical models. Next, we will demonstrate the significance of the phase-volume effect, i.e. the reduction of the CEP-dependence due to the spatial distribution of the CEP in focused few-cycle pulsed beams. We formulate a general description of the impact of the focal phase for laser-matter interactions of different nonlinear orders to answer the general question: if, when, and how much should one be concerned about the phase-volume effect? At last, CEP-dependent strong-field ionization of Xe using 3.2um few-cycle pulses as a benchmark will be studied. In order to find an alternative target for a single-shot CEPM at mid-infrared (MIR) wavelengths, Cs will be investigated. We observed an anomalous CEP-dependence in Cs, particularly at high intensities, which can be interpreted as the interference of two backscattered quantum orbits from adjacent optical cycles. Viewed from a higher perspective, this thesis demonstrates a precise characterization of the CEP and an accurate analysis of CEP-dependent light-matter interaction from the NIR, via the SWIR to the MIR range.}, year = {2023}, month = {2}, day = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00055932} } @Phdthesis { 373759866487_2023, author = {Zhu, B.}, title = {High resolution for x-ray spectroscopy studies with highly charged heavy ions at the CRYRING@ESR electron cooler}, abstract = {In this work, we report on the first x-ray spectroscopy study associated with the RR processes for bare lead ions at the electron cooler of the CRYRING@ESR, as storage rings are currently the only facilities routinely delivering hydrogen-like ions at high-Z in large quantities. With ultra-cold electron beam temperatures and near zero electron-ion collision energies, the effective production of characteristic projectile x-rays was well demonstrated at 0 deg and 180 deg observation geometries in our experiment by decelerated 10 MeV/u hydrogen-like lead ions. To reveal the role of radiative feeding transitions in the formation of observed intense Lyman and Balmer lines, an elaborate theoretical model describing the radiative decay dynamics and each (n, l, j)-state population varying over time is put to a test. As a result, the presented rigorous treatment reproduces observed x-ray spectroscopy really well in terms of the RR transitions and characteristic x-ray lines. In addition, we found a strong enhancement for l = n − 1 states in inner shells due to radiative Yrast-cascades from high Rydberg states, that finally contribute strikingly to the observed intensities of characteristic x-ray lines. Further on the current thesis lays the basis for a successful effort to push the experimental resolution of x-ray spectroscopy for L → K ground-state transitions at high-Z of below 80 eV at about 100 keV. This was done in an RR experiment of free electrons into the bound states of initially hydrogen-like uranium ions by adopting low temperature x-ray detectors, namely metallic magnetic calorimeters. Such an experiment allowed us for the first time to resolve the substructure of the Kα2 line and partially the Kα1 line in helium-like uranium ions. The preliminary data again prove the unique potential of the experimental method based on x-ray spectroscopy at the electron cooler of the CRYRING@ESR.}, year = {2023}, month = {2}, day = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, web_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00055769}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00055769} } @Phdthesis { 619122716543_2023, author = {Salgado, F.}, title = {Design of a single-particle detection system for strong-field QED experiments}, abstract = {One of the most intriguing physics processes that remain untested is the pure photon electron-positron pair production via quantum-vacuum fluctuations described by the nonlinear Breit-Wheeler theory. These fluctuations generate virtual pairs that can be turned into observable particles by applying strong electric fields above the Schwinger critical limit of \num\{1.3d18\}~V/m~\cite\{Schwinger.1951, Ritus.1985\}. Despite the advent of high-intense lasers, the critical limit is still far beyond achievable. However, such fields can be achieved on the rest frame of the real particles after the collision of a high-energy \$\gamma\$-ray photons with the laser beam. To diagnose the created pairs, this thesis describes the design of a particle detection system capable of successfully probing the single leptons created from strong-field quantum electrodynamics (SF-QED) interactions at the upcoming SF-QED experiments E-320 at FACET-II and FOR2783 at CALA. The designed detection system is composed of tracking layers made of LYSO:Ce scintillating screens and a Cherenkov calorimeter that, having their signals combined, can identify a positive event with a confidence level above 99{\%}. At the E-320 experiment, electron beams generated by the FACET-II linear accelerator with an energy of 13~GeV collide with an intense laser beam of \$\anot \approx 10\$, and nonlinear Breit-Wheeler pairs are produced in the nonperturbative full quantum regime of SF-QED interaction (\$\chie > 1\$ and \$\anot > 1\$). About 100 electron-positron pairs per shot are expected to be created. According to Monte-Carlo simulations of the experimental layout, the detection system will be placed on a region permeated by a shower of x-rays and few-MeV \$\gamma\$-photons, however, a signal-to-noise ratio of \$\SNRsig \approx 18\$ on the detectors is achieved.}, year = {2023}, month = {1}, day = {26}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00055695} } @Phdthesis { 21126, author = {Klar, L.}, title = {Quantum vacuum nonlinearities in the all-optical regime}, abstract = {In this work, we demonstrate how new theoretical concepts enable measurements of the signature of the QED vacuum nonlinearity beyond the background in collision experiments of all-optical high-intensity laser pulses. Using the vacuum emission picture, we develop the method of channel analysis of the signal. Based on these findings, we study two different experimental scenarios and identify discernible signals. In the first case, we consider the collision of two high-intensity laser pulses that differ only in their focus waist sizes. We present a numerical method to identify the regions where the signal dominates the background. Furthermore, we use this to investigate the behavior of the discernible signal, particularly with respect to the effects of the waist size of the probe beam. Of particular note, maximization of the measurable signal photons is not achieved by minimal focusing. This can be explained by the interplay of intensity in the interaction volume and decay behavior of the background in the far field. With the help of an elliptical cross section of the probe pulse, the signal can be further enhanced. Moreover, we show that a discernible signature of vacuum birefringence is achievable in the all-optical regime. In a second setup, elastic and inelastic photon-photon scattering mediated by the nonlinearity of the quantum vacuum is investigated. Based on a collision of four laser pulses of different oscillation frequencies, we observe signals in regions beyond the forward direction of the driving lasers as well as with frequencies beyond the laser frequencies. These features allow us to measure the signal beyond the background. The preceding channel analysis not only helps in the interpretation of the results, but it also allows effective amplification of the signal while maintaining experimental constraints.}, year = {2022}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://nbn-resolving.org/urn:nbn:de:gbv:27-dbt-20221130-104141-003}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 21052, author = {Kosheleva, V.}, title = {QED corrections to the hyperfine splitting and g factor of few-electron ions}, abstract = {Quantum electrodynamics (QED) is the first quantum field theory that describes all phenomena associated with electrically charged particles. Despite its mathematical complexity, it is quite effective in describing and predicting experimental results. With the introduction of lasers, atomic spectroscopy is constantly evolving, contributing to QED testing and continuous improvements in the precision of physical constants determination. Atomic systems offer many opportunities for high-precision QED tests. In the present dissertation, we focus on the magnetic sector of QED: the hyperfine structure and the Zeeman effect in few-electron ions. We present the systematic QED treatment of the electron correlation effects in the ground-state hyperfine structure in lithiumlike ions for the wide range of nuclear charge numbers Z = 7 - 82. The one- and two-photon exchange corrections are evaluated rigorously within the QED formalism. The electron-correlation contributions due to the exchange by three and more photons are accounted for within the Breit approximation employing the recursive perturbation theory. The calculations are performed in the framework of the extended Furry picture, i.e., with the inclusion of the effective local screening potential in the zeroth-order approximation. In comparison to previous theoretical computations, we improve the accuracy of the interelectronic-interaction correction to ground-state hyperfine structure in lithiumlike ions. The g factor of a bound electron is a rigorous tool for verifying the Standard Model and searching for new physics. Recently, a measurement of the g factor for lithiumlike silicon was reported and it disagrees by 1.7! with theoretical prediction [D. A. Glazov et al., Phys. Rev. Lett. 123, 173001 (2019)]. Attempting to resolve this deviation another theoretical value for silicon has been delivered. It results in a disagreement with experimental value [V. A. Yerokhin et al., Phys. Rev. A 102, 022815 (2020)]. We perform large-scale high-precision computations of the interelectronic-interaction and many-electron QED corrections to determine the cause of this disagreement. Similar to the case of hyperfine splitting, we carry out the calculations within the extended Furry picture of QED. And we carefully analyze the final values’ dependence on the binding potential. As a result, the agreement between theory and experiment for the g factor of lithiumlike silicon improves significantly. We also present the most accurate theoretical prediction for lithiumlike calcium too, which perfectly agrees with the experimental value.}, year = {2022}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=596}, note = {papertype:d, rsaps:1, filetype:pdf, hij:0, public:1,} } @Phdthesis { 21051, author = {Schwab, M.}, title = {Relativistic electron-cyclotron resonances in laser Wakefield acceleration}, abstract = {Laser plasma accelerators (LPAs) have the potential to revolutionize research fields that rely on relativistic particle beams and secondary radiation sources thanks to their 10-100 GV/m accelerating fields. In the Laser Wakefield Acceleration (LWFA) scheme, a relativistically intense pump or driver laser is focused into a low-Z gas target, ionizing the gas and driving a relativistic, electron plasma wave. Under the proper conditions, such a plasma wave can be used to accelerate electrons to GeV kinetic energies in only centimeters of plasma propagation. As LPAs continue to be tested and refined, nondestructive measurement techniques must be developed to further investigate and understand the dynamic laser-plasma interaction as well as to help ensure reliable operation and measurement of future accelerator facilities based on plasma technology. In this thesis, experiment, theory and simulation are combined to investigate the magnetized, relativistic plasma coinciding with the pump laser at the front of the plasma wave. Experimentally, the Jeti 40 TW laser system was used at the Institute of Optics and Quantum Electronics in Jena, Germany to drive a LWFA in tenuous plasma. The plasma wave was then shadowgraphically imaged using a transverse, few-cycle probe pulse in the visible to near-infrared spectrum and an achromatic microscope using various polarizers and spectral interference filters. The resulting shadowgrams were sorted depending on the properties of the LWFA’s accelerated electron bunches, and subsequently stitched together based on the timing delay between the pump and probe beams. This allowed for the detailed investigation of the laser-plasma interaction’s propagation and evolution as imaged in different polarizations and spectral bands. The resulting data showed two primary signatures unique to the relativistic, magnetized plasma near the pump pulse. Firstly, a significant change in the brightness modulation of the shadowgrams, coinciding with the location of the pump pulse, is seen to have a strong dependence on the pump’s propagation length and the probe’s spectrum. Secondly, after ~1.5 mm of propagation through the plasma, diffraction rings, whose appearance is polarization dependent, appear in front of the plasma wave. A mathematical model using relativistic corrections to the Appleton-Hartree equation was developed to explain these signals. By combining the model with data from 2D PIC simulations using the VSim code, the plasma’s birefringent refractive index distribution was investigated. Furthermore, simulated shadowgrams of a 3D PIC simulation using the EPOCH code were analyzed with respect to the aforementioned signals from magnetized, relativistic plasma near the pump pulse. The results of the study present a compelling description of the pump-plasma interaction. The previously unknown signals arise from relativistic, electron-cyclotron motion originating in the 10s of kilotesla strong magnetic fields of the pump pulse. Advantageously, a VIS-NIR probe is resonant with the cyclotron frequencies at the peak of the pump. With further refinement, the measurement of this phenomenon could allow for the non-invasive experimental visualization of the pump laser’s spatiotemporal energy distribution and evolution during propagation through the plasma.}, year = {2022}, month = {5}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://nbn-resolving.org/urn:nbn:de:gbv:27-dbt-20220705-135354-007}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 21050, author = {Vockert, M.}, title = {Die radiative Elektroneneinfang als Quelle stark linear polarisierter R\{\"\{o\}\}ntgenstrahlung}, abstract = {A good way to test the common theories in atomic physics and astronomy is to determine the degree of polarization of the emitted radiation. The short wavelengths in the X-ray range make a direct determination of the polarization impossible and the use of known interaction mechanisms necessary. A simple mechanism with significant anisotropy with respect to the polarization of the incident photons and a high effective cross section in the low to medium keV energy range is Compton scattering. Taking advantage of position- and energy-sensitive semiconductor detectors, this anisotropy provides the basis for Compton polarimetry. Double sided segmented semiconductor strip detectors have therefore been used for polarization determination for several years. Within the SPARC collaboration of FAIR, the design of a Si(Li) polarimeter has now been further developed. This novel Compton polarimeter with a cooled first preamplifier stage is characterized in detail in this work. Compared to the previous models, it allows for a better energy resolution and a more precise polarization determination, as well as for the first time a precise determination of the degree of polarization and the orientation of the polarization vector at photon energies well below 100 keV. This makes the emission properties of radiative transitions of heavy atoms accessible for polarization spectroscopy for the first time. Until now, the precision of the determination of the degree of polarization was largely limited by the statistics of the investigated data set. Studies based on simulations, which are presented in this thesis, show that for the sizes of experimental data sets available here, statistical uncertainty continues to dominate systematic sources of error. In particular, the improved detector setup allowed for the first time the determination of the degree of polarization for radiative electron capture into the K-shell (KREC) of ions for the previously inaccessible range of photon energies below 70 keV. Close to complete polarization has been demonstrated for this important electron capture process, which is very prominent in collisions of heavy ions and light targets. This demonstration was achieved for the interaction of a Xe54+ ion beam with an H2 gas target and a K-REC photon energy of 56 keV. In the present work, it has thus been shown that radiative electron capture (REC), in particular into the K-shell, is one of the most significant mechanisms of the production of strongly linearly polarized X-rays. In particular, with variation of projectile ion and energy and observation angle, it provides a well-defined source of polarized X-rays with tunable energy and, at the same time, variable polarization properties.}, year = {2022}, month = {4}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://nbn-resolving.org/urn:nbn:de:gbv:27-dbt-20220705-114843-009}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 21127, author = {Gebhardt, M.}, title = {Power scaling of few-cycle short-wavelength infrared laser sources for nonlinear frequency conversion}, abstract = {To be added}, year = {2022}, month = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://suche.thulb.uni-jena.de/Record/1798083973}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20776, author = {Hollatz, D.}, title = {Detection of positrons from Breit-Wheeler pair formation}, abstract = {This work explores the experimental observation of the Breit-Wheeler process, first described by Gregory Breit and John A. Wheeler in 1934 [1], where two photons collide to form an electron positron pair from the quantum vacuum. The specific challenge thereby is the low cross section of a few 10e 29 m2 or 0.1 b combined with the requirement of photon energies in the range of mega electronvolt. Such beams can be provided by particle accelerators, for instance LCLS at SLAC or the European XFEL at DESY. Experiments exploring photon photon collisions with conventional accelerators were done in the past, for example E144 at SLAC in 1997 [2], however the two photon process described by Breit and Wheeler has not yet been observed. Over the last few decades, novel laser driven plasma based particle accelerators (LWFA) made significant progress [3, 4, 5, 6], allowing the production of the required photon beams to study the Breit-Wheeler process at pure laser facilities [7, 8, 9]. The work in hand explores the challenges related to such an experiment specifically at high power laser facilities using the example of Astra Gemini, a multi 100TW dual beam system at the CLF in England. In an experiment, multi 100MeV γ-rays from LWFA electron bremsstrahlung and 1-2 keV x-rays from Germanium M-L shell transition radiation are collided to produce pairs through the Breit-Wheeler process. A detection system to measure those pairs composed of a permanent magnet beam line and shielded single particle detectors is developed and tested within this thesis. The acquired data allows an estimate of the requirements for future experiments to measure the two-photon Breit-Wheeler process.}, year = {2021}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00051347}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20732, author = {Klas, R.}, title = {Efficiency scaling of high harmonic generation using ultrashort fiber lasers}, abstract = {-}, year = {2021}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://suche.thulb.uni-jena.de/Record/1786717549}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 20764, author = {Hell, S.}, title = {Space- and Polarization-Resolved Investigations of Rear Side Optical Radiation from High-Intensity Laser-Solid Interaction}, abstract = {Thin aluminum foils (0.4-8µm) have been irradiated by laser pulses at relativistic intensities. Hot electrons, which are periodically accelerated in the laser field at the foil front side, emit coherent optical radiation (COR) at the foil rear side. COR has been investigated spaceand polarization-resolved to study hot electron transport through dense matter. This is important for further progress in laser-driven ion acceleration and fast ignition inertial confinement fusion. The COR source size increased from 1.2 µm to 2.3 µm with foil thickness. This is significantly smaller than the laser focal width of 4 µm and therefore indicates that pinching or filamentation influenced the propagation of the diverging hot electron current. The strong increase of the COR energy at the laser wavelength λ = 1030nm and λ/2 with laser intensity I\_L has been explained by considering an intensity dependent hot electron number N and temperature T\_h in a coherent transition radiation (CTR) model. Fitting this CTR model to the experimental data allowed to determine Th which increases with I\_L but slower than expected. The CTR model fits also showed that about 40{\%} of the hot electrons have been accelerated at the laser frequency 60{\%} at SHG, without significant changes with I\_L. Hence, hole boring must have deformed the plasma surface. The COR polarization, measured at SHG, shows strong spatial changes along the COR emission region and varies with I\_L, foil thickness and the COR source size at the foil rear surface.}, year = {2021}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00051373}, note = { papertype:m, rsaps:0, filetype:null, hij:0, public:1, } } @Phdthesis { 20604, author = {Tietze, S.}, title = {Compact XUV and X-Ray sources from laser-plasma interactions: theoretical and numerical study}, abstract = {In this thesis the generation of high order harmonics of ultrashort and high intensity laser pulses from solid density plasmas, so called surface high harmonic generation (SHHG), is studied. With SHHG, a compact source of coherent XUV and X-Ray radiation becomes possible. The results are obtained numerically using 1D and 2D Particle-In-Cell (PIC) computer simulations, which are supported by analytical models. This work focusses on two main issues of SHHG to date, pulse isolation and generation efficiency. It is shown that a single attosecond pulse (AP) can be obtained from a few-cycle incident laser pulse by choosing a suitable carrier-envelope phase (CEP), depending on the density and shape of density gradient of the target. An analytical model providing an interpretation of the results obtained from PIC simulations is presented. Spatial isolation of APs can be achieved using the attosecond lighthouse effect, but surface denting is detrimental to the separation of APs. PIC simulations are used to explain an experimental result, where a separation of pulses was not possible due to surface denting. Furthermore it is shown that the angular spectral chirp corresponds to the depth of the surface denting. The efficiency of SHHG can be enhanced greatly by reflecting the beam coming from a first target off a second target. Of major importance for the efficiency is the relative phase between harmonics on the surface of the second target. The relative phase changes even when propagating in free space due to the Gouy phase. To maximize the efficiency gain, a parametric study using PIC simulations has been performed to find the optimal distance between two targets.}, year = {2021}, month = {11}, DOI = {10.22032/dbt.50413}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20614, author = {Stallkamp, N.}, title = {Confined ensembles of highly charged ions for studies of light-matter interaction at high intensities: the HILITE Penning trap setup}, abstract = {The investigation of light-matter interactions is based on the description of the `photoelectric effect' in the early 20th century. The development of the first laser systems, especially of systems with high intensities and/or high photon energies, allowed to study previously unknown, non-linear effects like multiphoton or tunnel ionisation processes, which became subject of theoretical descriptions and experimental studies. Independently, the storage techniques for charged particles (electrons and ions) developed in parallel and different kind of devices, like Paul and Penning traps, had been invented in the 1950s and 1960s to study fundamental parameters of matter (for instance g-factor, mass etc.) with previously unknown accuracy. The HILITE experiment, presented within this thesis, is designed to combine and use for the first time the advantageous properties of target preparation a Penning trap can provide, like ensemble temperature, purity and localizability, in order to investigate laser-ion interactions at high intensities. Particular attention was paid to the compactness of the setup in order to be capable to transport the experiment to different laser facilities and perform experiments on site. In the frame of this thesis, the experimental setup was built and put into operation in terms of its dedicated ion source, ion selection, beam transport, deceleration and capture inside the Penning trap at the GSI Helmholtzzentrum f\{\"\{u\}\}r Schwerionenforschung GmbH. During commissioning, the storage and non-destructive detection of pure ion ensembles within the trap was demonstrated. The individual components have been characterised and their operation was checked. Additionally, a proposal was handed in for the first beamtime at an external laser facility (FLASH at DESY), which was granted and carried out. The interaction between the laser and low charged ions could be verified.}, year = {2021}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00050688}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20560, author = {Schmitt, A. T.}, title = {Kombination von hochpr\{\"\{a\}ziser Polarimetrie mit Spektroskopie im R\{\"\{o\}\}ntgenbereich}, abstract = {Magnetism, superconductivity, and other macroscopic quantum effects are based on symmetry breaking in solids. Their atomic and molecular structure can be studied using linearly polarized X-rays, where a change of the polarization state of the transmitted beam enables conclusions about electronic anisotropies in the material. Responsible for a change of the polarization state are the optical effects dichroism and birefringence. While X-ray absorption spectroscopy is a well-established method for the detection of dichroism, the effect of birefringence in the vicinity of an X-ray absorption edge is little studied. This work presents the first comprehensive experimental and theoretical investigation of X-ray birefringence and dichroism at the Cu K-absorption edge for two different model substances, CuO and La2CuO4. For this purpose, high-precision X-ray polarimetry, which detects changes of the polarization state with utmost sensitivity, was further developed into a spectroscopic method.}, year = {2021}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://suche.thulb.uni-jena.de/Record/1776273516}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20486, author = {Hornung, J.}, title = {Study of preplasma properties using time-resolved reflection spectroscopy}, abstract = {The aim of this work was to develop a new diagnostic method to probe preplasma properties in laser-plasma interaction experiments, using the time-resolved measurement of the laser pulse reflected by the plasma. Its spectral change over time can be attributed to the motion of the critical-density position of the plasma, which can be correlated with the preplasma properties that are present at the beginning of the interaction. 2-D particle-in-cell (PIC) simulations showed a correlation between the blue shift of the spectrum at the temporal beginning of the laser pulse and the expansion velocity of the preplasma, which can be used to derive the corresponding electron temperature. In addition, a correlation between the acceleration of the reflection point into the plasma and the density scale length has been observed. This has also been confirmed by an analytical description of the holeboring velocity and acceleration, which has been developed to include the effect of the preplasma scale length. To verify this method, two experimental campaigns were performed at the PHELIX laser system, while employing different temporal contrasts using so-called plasma mirrors. The experimental observations matched the predictions made by the numerical simulations. By comparing the maximum red shift of the spectrum with the results of the analytical description, the scale length of the preplasma was determined to be (0.18+-0.11) m and (0.83+-0.39) m with and without plasma mirror, respectively. At last, two further experimental campaigns to improve laser-ion acceleration at PHELIX were carried out. First, by increasing the laser absorption during the interaction using a p-polarized laser pulse and second, by increasing the laser intensity. The latter led to the generation of protons with a maximum energy of up to 93 MeV, for a laser intensity in the range of 8e20 W/cm^2, resulting in a new record for the laser system PHELIX.}, year = {2021}, month = {7}, DOI = {10.22032/dbt.50024}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20336, author = {Panahiyan, S.}, title = {Toward quantum control in discrete-time quantum walks}, abstract = {Discrete-time quantum walks are among the branches of quantum information and computation. They are platforms for developing quantum algorithms for quantum computers. In addition, due to their universal primitive nature, discrete-time quantum walks have been used to simulate other quantum systems and phenomena that are observed in physics and chemistry. To fully utilize the potentials that the discrete-time quantum walks hold in their applications, control over the discrete-time quantum walks and their properties becomes essential. In this dissertation, we propose two models for attaining a high level of control over the discrete-time quantum walks. In the first one, we incorporate a dynamical nature for the unitary operator performing the quantum walks. This enables us to readily control the properties of the walker and produce diverse behaviors for it. We show that with our proposal, the important properties of the discrete-time quantum walks such as variance would indeed improve. To explore the potential of this proposal, we apply it in the simulations of topological phases in condensed matter physics. With our proposal, we can control the simulations and determine the type of topological phenomena that should be simulated. In addition, we confirm simulations of topological phases and boundary states that can be observed in one-, two- and three-dimensional systems. Finally, we report the emergence of exotic phase structures in form of cell-like structures that contain all types of topological phases and boundary states of certain classes. In our second proposal, we take advantage of resources available in quantum mechanics, namely quantum entanglement and entangled qubits. In this proposal, we use entangled qubits in the structure of a quantum walk and show that by tuning the initial entanglement between these qubits and how these qubits are modified through the walk, one is able to produce diverse behaviors for the quantum walk and control its behavior.}, year = {2021}, month = {6}, DOI = {10.22032/dbt.49207}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 20227, author = {Olgun, H. T.}, title = {Efficient high energy laser-driven multicycle terahertz generation for accelerators}, abstract = {Optically generated, narrowband multi-cycle terahertz (MC-THz) radiation has the potential to revolutionize electron acceleration, X-ray free-electron lasers, advanced electron beam diagnostics and related research areas. However, the currently demonstrated THz generation efficiencies are too low to reach the requirements for many of these applications. In this project, a MC-THz generation approach via difference frequency generation (DFG) driven by a laser with a multi-line optical spectrum was investigated with the aim of increasing the conversion efficiency. For this purpose, a home-built, Yb-based laser source with a multi-line optical spectrum was developed. This laser source was amplified to tens-of-millijoule using a regenerative and a four-pass amplifier; it was used to generate MC-THz in magnesiumoxid-doped periodically poled lithium niobate (MgO:PPLN) and rubidium-doped periodically poled potassium titanyl phosphate (Rb:PPKTP). With this laser system, the highest optical-to-THz conversion efficiencies (CE) of 0.49{\%} with a pulse energy of 30 mJ at 0.29 THz, and 0.89{\%} with a pulse energy of 45 mJ at 0.53 THz in MgO:PPLN were achieved. These results compare well with 2-dimensional numerical simulations. In addition, Rb:PPKTP, which has a promising figure-of-merit compared to MgO:PPLN, achieved a CE of 0.16{\%} with a pulse energy of 3 mJ at 0.5 THz. Next, to scale this laser system to tens of millijoule MC-THz output, large aperture crystals for both MgO:PPLN and Rb:PPKTP were investigated using a commercial laser, producing 200 mJ with a pulse duration of 500 fs at 1030 nm; although in this case an older method of optical rectification (OR) was used, achieving less efficiency than the multi-line source. With MgO:PPLN crystals of aperture size 10x15mm2, a CE of 0.29{\%} at 0.35 THz was achieved with a pulse energy of 260 mJ. This is the highest known CE value using OR. In addition, wafer-stacks with alternating crystal-axis orientation of aperture size of 1” for LN and 10x10mm2 for KTP were successfully tested. Two novel experiments were performed with LN wafers: multi-stage wafer-stacks in a serial configuration with multi-output THz radiation and back-reflected seeded MC-THz generation. Both methods improved the efficiency of the MC-THz generation, compared to a single stack. In particular, for the backreflected seeded MC-THz generation, pulse energies of 280 mJ with a CE of 0.29{\%} was achieved; thus demonstrating the potential of seeded MC-THz generation. These achievements are an important step for the realization of next-generation, THz-driven electron accelerators.}, year = {2020}, month = {12}, school = {Universit\{\"\{a\}t Hamburg; Fakult\{\"\{a\}t f\{\"\{u\}\}r Mathematik, Informatik und Naturwissenschaften}, file_url = {https://ediss.sub.uni-hamburg.de/handle/ediss/8832}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19669, author = {Tuitje, F.}, title = {Diffraction-based metrology in the extreme ultraviolet}, abstract = {The growing numerical development of Coherent Diffraction Imaging (CDI) towards ptychography allows for the first time the separate reconstruction of object and the wavefront illuminating it. This work is dedicated to the investigation of further possibilities resulting from the complex reconstruction of object and illumination. In this thesis, gold structures buried in silicon are reconstructed and examined with regard to their surface morphology in reflection geometry. This completely non-destructive method allows metrology on structures of embedded circuits and otherwise hidden defects. The increasing demand for easily accessible and compact high-performance light sources around the silicon and water window opens the question regarding their suitability for lensless imaging. In the following chapters a method is introduced which allows an almost complete source analysis by means of a single long time exposed diffraction pattern. The knowledge gained in this way allows an improvement of the source with respect to water window CDI and provides insight into dynamic processes within the source. The complex-valued reconstruction of the wavefront allows an insight into the plasma and the ionization states prevailing there. The XUV seed pulse of a seeded Soft-X-Ray laser (SXRL), which passes the pumped plasma and changes its properties with respect to the states in the plasma, is reconstructed ptychographically. Adapted Maxwell-Bloch simulations allow by comparison with the measurement to restore the ionization states during the passage of the seed pulse. Previous experiments showed artifacts during reconstruction, which were directly related to the periodicity of the objects. Simulation of periodic objects of different sizes and with the addition of intentional defects showed a dependence of the reconstruction of the object on the illumination function. Various criteria were derived from this simulation and are presented in this thesis.}, year = {2020}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00046898}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Thesis { 19737, author = {Beyer, M.}, title = {Characterization of optical componentsof a laser amplifier via spectral interferometry}, abstract = {The fundamentals of ultrafast optics based on Maxwell’s equations are presented, Gaussian beams, optical pulses and their propagation in dispersive media are introduced. The method of spectral interferometry (SI) is fundamentally introduced and explained in section 3, different possibilities for characterizing the spectral phase are presented. The experimental setup for the characterization and a referencing measurement to well characterized materials is done in section 4. It is also investigated in section 4 which experimental issues can occur, how large their influences on the measurement are and how they can be resolved. The derived methods of spectral phase characterization are used in section 5 to specify the optical components of an amplifier in a CPA laser system. The components of the laser amplifier are categorized and their effects on the spectral phase are compared and discussed. It is then summarized why dispersion measurements are important and how the method of SI can be utilized to select suitable components for a laser amplifier.}, year = {2020}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00047186}, note = { papertype:b, rsaps:0, filetype:null, hij:0, public:1, } } @Thesis { 19736, author = {Nolte, M.}, title = {Charakterisierung expandierter ultrad\{\"\{u\}\}nner DLC-Folien f\{\"\{u\}\}r die Laser-Protonenbeschleunigung}, abstract = {In dieser Arbeit werden zun\{\"\{a\}chst die physikalischen Grundlagen vorgestellt, welche f\{\"\{u\}\}r das Verst\{\"\{a\}ndnis der Simulationen und deren Auswertung notwendig sind. Das Plasma, welches sich vor dem Erreichen der maximalen Laserintensit\{\"\{a\}t ausgebreitet hat, kann den TNSA-Prozess und dessen Effektivit\{\"\{a\}t beeinflussen. Es ist daher wichtig die genaue Form und den Zustand des Targets zum Zeitpunkt des Eintreffens des Hauptpulses zu charakterisieren. Daf\{\"\{u\}\}r wird der Computercode MULTI-fs verwendet, welcher noch einmal genauer in Abschnitt 3 diskutiert wird, um die Interaktion eines relativistischen Laserpulses mit einem d\{\"\{u\}\}nnen Target zu simulieren. Die zeitliche Struktur des in der Simulation verwendeten Laserpulses wurde bei Experimenten am POLARIS-Laser in Jena gemessen. Betrachtet wird dabei die ansteigende Flanke der Laserintensit¨at bis zu dem Zeit-punkt, an dem die Laserintensit\{\"\{a\}t 10^17W/cm^2 ¨uberschreitet, f\{\"\{u\}\}r verschiedene Targetdicken und verschiedene maximale Laserintensit\{\"\{a\}ten. Aus diesen Simulationen wird die Verteilung der Elektronendichte gewonnen und parametrisiert, um die Form der Plasmaverteilung systematisch beschreiben zu k\{\"\{o\}\}nnen. Die aus der Simulation gewonnenen Ergebnisse werden vorgestellt und diskutiert.}, year = {2020}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00047187}, note = { papertype:b, rsaps:0, filetype:null, hij:0, public:1, } } @Phdthesis { 19653, author = {Hollinger, R.}, title = {Extreme nonlinear optics in highly excited semiconductors}, abstract = {This thesis studies extreme nonlinear optical phenomena in highly excited ZnO semiconductor samples. ZnO with a band gap of 3.2 eV, in the near-ultraviolet spectral range, is irradiated with far-off resonance strong light fields in the near (0.8 µm, 1.5 eV) to the far-infrared (10 µm, 0.13 eV). Specifically, the coherent conversion of laser light into high orders of the fundamental frequency, also known as high harmonic generation (HHG) and optically pumped lasing were investigated.}, year = {2020}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00046571}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19567, author = {B\{\"\{o\}\}ning, B.}, title = {Above-threshold ionization driven by spatially structured laser fields}, abstract = {Strong laser fields are a valuable tool to study the electron dynamics in atoms and molecules. A prominent strong-field process is the above-threshold ionization (ATI), where the momentum distributions of emitted photoelectrons encode not only details about the laser-atom interaction, but also properties of the driving laser field. Recent advances in the generation of intense laser beams at mid-infrared wavelengths enable the investigation of ATI in a new parameter range. Moreover, laser beams with a sophisticated spatial structure as a result of an orbital angular momentum (twisted light) have found applications in the strong-field regime. In this dissertation, we theoretically investigate ATI driven by mid-infrared and twisted light beams. We show that not only the temporal but also the spatial dependence of such beams has a pronounced impact on the ionization dynamics due to nondipole interactions. Therefore, we develop a quite general theoretical approach to ATI that incorporates this spatial structure: in order to extend the widely used strong-field approximation (SFA), we construct nondipole Volkov states which describe the photoelectron continuum dressed by the laser field. The resulting nondipole SFA allows the treatment of ATI and other strong-field processes driven by spatially structured laser fields and is not restricted to plane-wave beams. We apply this nondipole SFA to the ATI driven by mid-infrared plane-wave laser beams and show that peak shifts in the photoelectron momentum distributions can be computed in good agreement with experiments. As a second application, we consider the ATI driven by standing light waves, known as high-intensity Kapitza-Dirac effect. Here, we calculate the momentum transfer to photoelectrons for elliptically polarized standing waves and demonstrate that low- and high-energy photoelectrons exhibit markedly different angular distributions, which were not observed previously. Finally, we investigate the ATI of localized atomic targets driven by intense few-cycle Bessel pulses. Based on a local dipole approximation, we demonstrate that the photoelectrons can also be emitted along the propagation direction of the pulse owing to longitudinal electric field components. Moreover, when measured in propagation direction, the ATI spectra depend on both the opening angle and the orbital angular momentum of the Bessel pulse. To conclude, we also discuss the extension of this work towards long pulses, which can be treated within the above nondipole SFA.}, year = {2020}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00045092}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Thesis { 19491, author = {Krause, J.}, title = {Oberfl\{\"\{a\}chendynamik eines Plasmas im Bereich des steilen Dichtegradienten bei Wechselwirkung mit relativistischen Intensit\{\"\{a\}ten}, abstract = {In this thesis the spectra of light reflected back from a laser plasma are analyzed with respect to the surface dynamics in the region of the increasing density gradient. In addition, the indentation movement as a function of energy, polarization and foil thickness was investigated.}, year = {2020}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=580}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 19382, author = {Ringleb, S.}, title = {The HILITE Setup for High-Intensity-Laser Experiments with Highly Charged Ions: Design and Commissioning}, abstract = {Quantitative studies of the interaction of atomic and molecular ions with laser radiationat high laser intensities and/or high photon energies are a novel area in the field of laser-matter-interaction. They are facilitated by precise knowledge of the properties of the ions as a target for the laser. This refers to the location, composition, density and shape of the ion cloud as a target, as well as to the capability of characterising the ion target before and after the laser interaction. Ion traps are versatile instruments when it comes to localising ions with a defined particle composition, density and state within a specific and small volume in space. They allow in particular the combination of ions in well-defined quantum states with intense photon fields. The present thesis contains the detailed description of the setup and commissioning of the HILITE (High-Intensity Laser Ion-Trap Experiment) Penning trap, which is dedicated to providing a well-defined cloud of highly charged ions for a number of different experiments with intense lasers. Various experimental procedures are necessary to create such an ion cloud, starting with the production of highly charged ions, their transport, selection, capture, storage, cooling, compression and detection. In the present thesis, the experimental setup is described in detail and the components required for ion target preparation, characterisation and non-destructive ion detection inside the trap are characterised. Special attention is paid to the counting limits of the detection electronics, because knowledge of the exact number of stored ions is essential for the planned experiments. Highly charged ions are produced in an electron-beam ion trap (EBIT), selected with respect to their mass-to-charge ratio, decelerated, and injected into the trap, where they are dynamically captured and stored. For the preparation of a well-defined ion cloud, the initially high energetic ions must be slowed and cooled to an energy of less than 1 meV. This thesis describes the applied methods of active-feedback cooling and resistive cooling and examines their potential cooling efficiencies.}, year = {2020}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00045138}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19365, author = {Hofbrucker, J.}, title = {Two-photon ionization of many-electron atoms}, abstract = {Until recently, the nonlinear interaction between light and matter has been restricted to only low photon energies produced by optical lasers. However, about a decade ago, the rise of free-electron laser facilities revolutionized the field of nonlinear light-matter interaction by delivering intense high-energy light pulses. Today, such lasers are used for research in materials science, chemical technology, biophysical science, solid-state physics as well as fundamental research. It is the new experimental possibilities provided by free-electron lasers that motivated the work presented in this thesis. Two-photon ionization process is one of the simplest nonlinear interactions in which absorption of two photons by an atom (or a molecule) leads to promoting one of its bound electrons to continuum. This work presents studies of two-photon ionization of neutral atoms. After a brief historical introduction to the topic of nonlinear light-matter interaction, the density matrix describing the state of an atom and a photoelectron following two-photon ionization is derived. The density matrix contains the complete information about the overall system consisting of a photoion and a photoelectron. In each successive chapter, part of this density matrix is used to obtain characteristic quantities such as total two-photon ionization cross section, photoelectron angular distributions, ion polarization or even degree of polarization of fluorescence photon produced by subsequent decay of the photoion. Physical properties of these quantities are studied and intriguing phenomena, such as elliptical dichroism, polarization transfer as well as relativistic and screening effects are investigated. In one-photon ionization, the photon energy for which the dominant ionization channel vanishes is called the Cooper minimum. This concept is extended to nonlinear ionization of atoms and the effect of the minimum on all above mentioned quantities is studied. In this work it is shown, that the nonlinear Cooper minimum leads to strong variation in practically all observables of the two-photon ionization process. For example, the polarization transfer from the incident to fluorescence photon can be maximized and so can be the elliptical dichroism in photoelectron angular distributions. Furthermore, it is theorized, that detection of the energy position of the nonlinear Cooper minimum could lead to comparison of experimental measurements and theoretical calculations at hitherto unreachable accuracy.}, year = {2020}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00044410}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19367, author = {Paufler, W.}, title = {High-Harmonic Generation with Laguerre-Gaussian Beams}, abstract = {High-harmonic generation is a versatile process, for one thing, useful to explore the structure of atoms or molecules during the generation itself and apart from that a source of bright, short, coherent extreme ultraviolet radiation. Thereby the harmonic radiation can be controlled by the shape of the driving laser with respect to its polarization or frequencies. Recent advances show that Laguerre-Gaussian beams, which carry in addition to their spin also orbital angular momentum, can be utilized for high-harmonic generation. In this thesis, we analyze high-harmonic generation with Laguerre-Gaussian beams in the framework of the strong-field approximation and show that this requires both the interaction of a single atom with the driving laser and the macroscopic superposition of all single atom contributions. We first investigate high-harmonic generation with linearly polarized Laguerre-Gaussian beams. There, we show how the orbital angular momentum of the driving laser is transferred to the generated harmonics. Here, we developed vivid photon diagrams to explain the conservation of orbital angular momentum. We then consider phase matching of the generated radiation in order to increase the conversion efficiency. In particular, we analyze the coherence length at different positions in the generating beam. Furthermore, we investigate high-harmonic generation with a pair of counter-rotating circularly polarized Laguerre-Gaussian beams. Here, we derive selection rules that take account of the conservation of energy, spin and orbital angular momentum. In addition, we show that the orbital angular momentum of the generated harmonics can be precisely controlled by the orbital angular momentum of the driving beam.}, year = {2020}, month = {5}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00044037}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19153, author = {Tamer, I.}, title = {Petawatt-Class Laser Optimization and Ultrashort Probe Pulse Generation for Relativistic Laser-Plasma Interactions}, abstract = {Advancements in high peak power laser development have resulted in laser systems capable of accelerating charged particles in a plasma to nearly the speed of light. For a comprehensive understanding and optimization of such interactions towards higher experimental yields, further enhancements in the laser system performance are required, along with a method that enables a direct view into the laser-induced plasma with a high spatial and temporal resolution. The work presented in this thesis details the results of multiple investigations regarding upgrades to the petawatt-class POLARIS laser and the development of a multi-beam ultrashort laser system for probing relativistic laser-plasma interactions at Friedrich Schiller University and Helmholtz Institute in Jena, Germany. As laser pulse intensities are improved worldwide, the spatial, temporal, and temporal intensity contrast profiles of the pulses become increasingly crucial to the experimental performance and future scalability of the laser system. Where possible, an optimization of these parameters should be accomplished using simple, robust methods to avoid large-scale changes to the operational petawatt-class system. To improve the fluence homogeneity of the POLARIS laser pulse, a comprehensive spatio-temporal model of the pump-induced wavefront aberrations was constructed and the results of the verified model were applied to correct the heavily aberrated amplified beam profile in a joule-class multi-pass amplifier through a precise adjustment the pump distribution. Furthermore, the pulse duration post-CPA could be further compressed by a factor of 3 after near field SPM in a highly nonlinear material. In parallel to the spatial and temporal profile improvements, the temporal intensity contrast of the POLARIS laser pulse was enhanced 1000-fold using a plasma mirror. An insight into the complex dynamics of relativistic laser-plasma interactions produced by the enhanced POLARIS laser can be achieved by employing an additional ultrashort laser system as an optical probe. For this purpose, a multi-beam ultrashort optical probing system, seeded by the POLARIS oscillator and pumped by a dedicated Yb:FP15-based CPA system, has been developed and installed within the petawatt-class laser system. The probing setup simultaneously offers two millijoule-level, nearly 100 fs laser pulses, along with a few-cycle laser pulse for high precision optical probing. Here, noncollinear optical parametric amplification (NOPA) is utilized to generate 20 µJ, 230 nm FWHM bandwidth pulses centered at 820 nm. The nonlinear BBO crystal is employed not only as the gain medium, but also as the pulse compressor, delivering near-FTL 11 fs pulses in a setup smaller than 40 cm × 40 cm. The temporal synchronization of the ultrashort probe pulses with the main POLARIS pulse are characterized using a live diagnostic system that monitors several orders of magnitude of delay. With the enhanced petawatt-class laser pulse, now equipped with a few-cycle optical probe, the intricate details of relativistic laser-plasma interactions can be revealed at the POLARIS laser system.}, year = {2020}, month = {3}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00040833}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19091, author = {Lei, B.}, title = {High energy radiation from compact plasma-based sources}, abstract = {Throughout the current century, compact, high-energy radiation sources have become critically important for many advanced applications in medicine, industry, education, and scientific research. In contrast to conventional radiation sources mainly produced in huge facilities, plasma-based radiation sources with centimetre lengths can provide great flexibility and drive science forward. In this thesis, several plasma wakefield-based undulator schemes have been developed in parallel. First, the guiding of laser beams, including a single Gaussian pulse, Hermite-Gaussian (HG) modes, and Laguerre-Gaussian (LG) modes, is studied through the Schr\{\"\{o\}\}dinger-like wave equation for a harmonic oscillator with paraxial and quasistatic approximations in a parabolic plasma density channel. If the laser pulse is injected into the plasma channel with a transverse offset or an angle with respect to the propagation axis, it will undergo centroid oscillation. Special conditions are found to control the interesting properties of such oscillation: frequency, amplitude, and polarisation. Second, wakefield excitation driven by the oscillating laser pulse is theoretically and numerically studied in the linear/nonlinear regime. The specific field structure of each scheme is demonstrated. For a short, wide laser pulse, the wakefield provides a linear focusing force near the propagation axis that drives the betatron oscillation of the injected electrons. The extra driving force is introduced by the centroid oscillation of the laser pulse. Surprisingly, the undulator field generated by beating several different HG modes becomes monochromatically sinusoidal when the strength of laser pulses matches a special condition. This is very beneficial for the generation of a narrow radiation spectrum. Third, the dynamics of both a single electron and an electron beam are studied in these generated undulator fields. Generally, an electron undergoes the combined motion of betatron and undulator oscillations. However, the weak betatron oscillation could be totally removed if certain injection conditions for an electron can be satisfied. Further theoretical work on the dynamics of an accelerated electron indicates that there is a resonance between the betatron oscillation of the electrons and centroid oscillation of the laser pulse. This resonance can be used to increase the oscillation amplitude and strength for the electron rapidly within the first several Rayleigh lengths of propagation. While being accelerated in the wakefield, the resonance is broken and results in a semi-steady oscillation with large amplitude and strength, which enables the generation of strong γ-ray radiation. Ultimately, the radiation spectrum from the oscillation of an electron beam is calculated. The proposed schemes are capable of generating an x-ray radiation spectrum with a narrow bandwidth or synchrotron-like x/γ-ray radiation of high energy. The energy and brightness are comparable with currently available conventional radiation sources. It is also demonstrated that these flexible schemes can be tuned to generate radiation carrying well-defined angular momentum.}, year = {2019}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00040306}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 18911, author = {Bilal, M.}, title = {High precision many-electron calculations for multiply-charged ions}, abstract = {Recent advances in measurements/observations have made it possible to test small and minute fundamental physical eff ects for transition rates and line strengths in many-electron atomic systems with unprecedented accuracies. This thesis provides high-precision calculations of line strengths and lifetimes for diff erent atomic systems where we accurately account for various higher-order eff ects. In all these systems, systematically enlarged multiconfi guration Dirac-Hartree-Fock (MCDHF) wave functions are employed for calculation of the atomic states involved in the transitions to account for the relativistic correlation corrections. Firstly, the QED sensitive magnetic dipole (M1) line strengths between the fi ne-structure levels of the ground confi gurations in B-, F-, Al- and Cl-like ions are calculated for the four elements argon, iron, molybdenum and tungsten. For these transitions, in addition to relativistic correlation corrections, the QED corrections are evaluated to all orders in αZ utilizing an eff ective potential approach. As a result, our calculations have reached an accuracy of 10−4 for the M1 line strengths. These accurate theoretical predictions provide the prerequisite for a test of QED by lifetime measurements at diff erent frequencies and timescales. This will help to find a reason for the present discrepancies between theory and experiment for B-like Ar and Al-like Fe. Secondly, the line strength of the 1s 2 2s2p 1 P 1 – 1s 2 2s 2 1 S 0 spin allowed E1 transition in Be-like carbon is calculated. For this highly correlated transition, different correlation models are developed to account for all major electron-electron correlation contributions. The fi nite nuclear mass eff ect is accurately calculated taking into account the energy, wave functions as well as operator contributions. As a result, a reliable theoretical benchmark of E1 line strength with a relative accuracy of 1.5×10−4 is provided to support high precision lifetime measurement at GSI Darmstadt for the 1s 2 2s2p 1 P 1 state in Be-like carbon. Finally, large-scale calculations are performed for all allowed (E1) and forbidden (M1, E2, M2) transitions among the fi ne structure levels of the 3s 2 3p 5 , 3s3p 6 and 3s 2 3p 4 3d confi gurations for Ni XII. Here, we validate all recently identifi ed tentative experimental lines with one exception. Moreover, we present ab initio lifetimes that are better than previously reported ab initio and semi-empirical values as compared to available experimental data. Thus, we provide reliable predictions in the prospects of future experiments.}, year = {2019}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00040082}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 18866, author = {Tadesse, G.}, title = {Nanoscale Coherent Diffractive Imaging using High-harmonic XUV Sources}, abstract = {Imaging using sources in the XUV and X-ray spectral range combines high resolution with longer penetration depth (compared to electron/ion microscopy) and found applications in many areas of science and technology. Coherent diffractive imaging (CDI) techniques, in addition, lift the performance limitation of conventional XUV/X-ray microscopes imposed by image forming optics and enable diffraction limited resolutions. Until recently, CDI techniques were mainly confined to large scale facilities e.g. synchrotrons and X-ray free electron lasers due to unavailability of suitable table-top XUV/X-ray sources. Tabletop sources based on high-order harmonic generation (HHG) nowadays offer high and coherent photon flux which widened the accessibility of CDI techniques. First imaging experiments already showed the potential of HHG-based setups albeit with limited resolution on features much larger than the illuminating wavelength. So far, table-top CDI systems were not able to resolve sub-100 nm features using performance metrics that can qualify these systems for real world applications. The huge progress in scaling the coherent flux of HHG sources driven by high power femtosecond fiber laser systems presented unique opportunities for reaching new regimes in imaging performance. However, experimental issues with power handling and the onset of so-far-unexplored resolution limits for wavelength-scale features were some of the challenges that needed to be addressed. In this work, CDI experiments with the highest resolutions in different modalities using a highnflux fiber laser driven HHG source are presented. In conventional CDI, a record-high resolution of 13 nm is demonstrated together with the possibility of high speed acquisition with sub-30 nm resolution. In a holographic implementation of CDI, features with a half-distance of 23 nm are resolved which are the smallest features to ever be resolved with a table-top XUV/X-ray imaging system. In addition, waveguiding effects are shown to affect image quality and limit the achievable resolution in these wavelength-sized features. Ptychographic imaging of extended samples is also performed using a reliable Rayleigh-like resolution metric and resolving of features as small as 2.5 λ (sub-50 nm) is demonstrated. Together with the significant reduction in measurement times, the imaging results presented push the performance of table-top CDI systems a step closer to that required for real world applications. The scalability of the HHG flux at higher photon energies (soft X-rays) with the power of the driving fiber laser system promises to deliver imaging setups with few nanometer resolutions in the near future. These systems can find applications in material and biological sciences, study of ultrafast dynamics, imaging of semiconductor structures and EUV lithographic mask inspection.}, year = {2019}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00040692}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 18925, author = {M\{\"\{a\}usezahl, M.}, title = {Untersuchung lasergetriebener Protonenbeschleunigung bez\{\"\{u\}\}glich Vorplasmaerzeugung und r\{\"\{a\}umlicher Protonendetektion}, abstract = {Die lasergetriebene Beschleunigung von Protonen mittels TNSA hat ein erhebliches Potential, die physikalische Grundlagenforschung um ein weiteres Instrument zur Untersuchung hochenergetischer Wechselwirkungen zu erg\{\"\{a\}nzen. Um die erreichten Protonenenergien und die Stabilit\{\"\{a\}t f\{\"\{u\}\}r derartige Anwendungen weiter zu steigern, ist ein grundlegendes Verst\{\"\{a\}ndnis der innerhalb weniger Pikosekunden ablaufenden Prozesse n\{\"\{o\}\}tig. Im Rahmen dieser Masterarbeit wurde ein Teil der Diagnostik f\{\"\{u\}\}r die Entstehung solcher Protonenstrahlen untersucht. Dadurch stehen in Zukunft weitere Instrumente zur Charakterisierung von Protonen am POLARIS-System zur Verf\{\"\{u\}\}gung.}, year = {2019}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=589}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 19090, author = {W\{\"\{u\}\}rzler, D.}, title = {Untersuchung und Simulation der Ionisations- und Streudynamik von Photoelektronen mithilfe von Zwei-Farben-Feldern}, abstract = {If atoms or molecules are exposed to strong laser fields, various processes can occur after ionization, and the dynamics of these processes depend on the trajectory of the emitted electrons. Both the ionization rates and the electrons trajectory depend strongly on the shape of the laser field. Thus, tailoring strong laser fields on the sub-cycle and sub-femtosecond time scale, the insight and control of the underlying dynamics of these processes has been significantly increased in the last two decades. Here, orthogonal and parallel two-color laser fields represent an effective approach to manipulate the ionization rates and the subsequent electron movement in the laser-dressed continuum. This is achieved by varying the relative phase, ϕrel , between both field components ( ω and 2 ω ). In this thesis orthogonal and parallel two-color laser fields are used to study the ionization and scattering dynamics of noble gases. Further, phases-dependent photoelectron spectra- captured by a velocity map imaging spectrometer, are studied by applying the recently introduced phase-of-the-phase analysis [1]. The measured results are compared with three dimensional semi-classical calculations, which can be performed for arbitrarily polarized laser fields, while taking higher order scattering events into account. These simulation also allows for the separation and investigation of different classes of photoelectrons (e.q. direct and scattered electrons), which alows for analysis of the underlying dynamics. In one vmi measurement in this thesis, an orthogonal two-color laser field ( λω = 800 nm, λ2ω = 400 nm)with an unconventional orientation, i.e. with the polarization of the ionizing laser field perpendicular to the detector surface and the steering field parallel to it, is used. This allows for the investigation of the phase-dependent photoelectron spectra, as the deflections of photoelectrons due to the 2 ω -field are directly mapped onto the detector. The phase dependence of the photoelectron spectra of neon and xenon shows clear phase shifts between scattered and direct electrons. When comparing the phase dependency of neon and xenon, a strong target dependency is observed. Namely xenon show vastly more complex phase dependence then neon. Further investigations of xenon where perfomed using parallel two-color field within the short-wave infrared range ( λω = 1800 nm, λ2ω = 900 nm). To measure electrons with high energy, which are created during ionization with these long wavelengths, a high-energy VMI spectrometer was developed based on the design presented in [2]. Using this device, electron energies up to 320 eV can be detected. The intention of this measurement is to retrieve the ionization time of the photoelectrons contributing to the characteristic fork structure [3] based on the phase dependencies of the contributing photoelectrons. Using these wavelengths, the fork structure can be easily detected and provides a well-suited benchmark for this study. Based on the semi-classical model it is shown that phase-dependent photoelectron signal, which encodes information about the contributing ionization times, is convoluted with the phase dependencies resulting from perturbation of the electron trajectories propagating in the laser-dressed continuum. Independent on the degree of the perturbation this can mislead assignment of the ionization time by up to 80 as.}, year = {2019}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00039885}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 19007, author = {M\{\"\{u\}\}ller, R. A.}, title = {Investigation of Atomic Nuclei via Electronic Processes}, abstract = {In atomic physics, nuclei are often described as a point-like charges with an infinite mass that binds the electrons. With more and more precise experimental techniques, however, this approximation is no longer sufficient and it is necessary to develop a better theoretical understanding of the ways atomic nuclei interact with the electron shell. We do observe for example small shifts in the lines of spectra of different isotopes of the same atomic species. In this thesis, we present calculations for these isotope shifts and use them to derive the difference between the nuclear charge radii of two thorium isotopes, ²³²Th and ²²⁹Th as well as ²²⁹Th and the isomeric state ²²⁹mTh. These results are of particular interest for the development of a future nuclear clock and coherent high-energy light sources. Moreover, we discuss precise isotope shift calculations for singly charged barium and compare them with a recent experiment. We motivate the relevance of such studies for the search for physics beyond the Standard Model. Spectral lines, however, do not only shift but also split due to the non-point-like nature of atomic nuclei. From the spectroscopy of this hyperfine splitting, it is possible to extract the multipole moments of the nuclear electromagnetic field. As a part of this thesis, we present the first value of the nuclear magnetic dipole moment of the ²²⁹mTh nuclear isomer that does not rely on previous calculations or measurements. Having extracted several important properties of the ²²⁹Th nucleus and the isomer ²²⁹mTh using atomic theory we invert our view in the second part of this thesis. Namely, we want to use processes in the electron shell to populate the ²²⁹mTh isomeric state. Preparatory to our calculations for the actual excitation of the isomer, we discuss the atomic structure of thorium. Of particular experimental interest is the level structure of singly charged thorium. In a recent study, we show the results of atomic structure calculations that help to interpret measured thorium spectra and can be used to estimate the probability of a nuclear excitation via the electron shell in this system. A deeper and more accurate discussion is performed for the comparably simple triply charged thorium ion. This study helps to test the various approximations necessary to discuss systems with a more complicated electronic structure. Bringing everything together the final publication presented in this thesis proposes an experimental setup to excite the ²²⁹Th nucleus in a controlled way depending on the yet to be found energy of the nuclear isomeric state. This method is currently applied in an experiment at the German National Metrology Institute.}, year = {2019}, month = {8}, school = {Technische Universit\{\"\{a\}t Carolo-Wilhelmina zu Braunschweig; Fakult\{\"\{a\}t f\{\"\{u\}\}r Elektrotechnik, Informationstechnik, Physik}, file_url = {t3://file?uid=594}, note = {papertype:d, rsaps:1, filetype:pdf, hij:0, public:1,} } @Phdthesis { 18769, author = {Beerwerth, R.}, title = {Electron Correlation in Relativistic Multiconfiguration Calculations of Isotope Shift Parameters, Hyperfine Coupling Constants and Atomic Processes}, abstract = {Electron correlation denotes the corrections to central field approximations applied in Hartree\{--\}Fock methods that arise from the electron-electron interaction. As a consequence, wave functions for atomic states are represented as a mixture of different electronic configurations. Corresponding highly correlated multiconfiguration wave functions allow precise computations of atomic parameters such as energy levels, transition rates, isotope shift parameters and hyperfine coupling constants. In this work, multiconfiguration Dirac–Hartree–Fock computations are utilized to compute precise isotope shift parameters and hyperfine coupling constants for actinium, nobelium and iron. As a prerequisite, extensive computations of the atomic level structure for actinium were performed to assign the computed energies to measured transitions, and as a consequence several unknown levels are predicted. In order to estimate uncertainties of the computed results, systematically enlarged configuration spaces are utilized and the results of several model computations that probe different correlation effects are compared. Furthermore, electron correlation is crucial to describe higher order processes such as shake transitions that accompany photoionization or Auger processes. These processes are in addition caused by the non-orthogonality of the single electron orbitals obtained in Hartree–Fock computations. The latter can be transformed into electronic correlation by a biorthonormal transformation and we evaluate its application to the efficient computation of Auger transition rates. With this approach, large scale calculations for complex atoms with multiple open shells can be extended to include shake transitions. These transition rates are utilized in Auger cascade models that describe the ionization or excitation of core electrons from atoms or ions into highly excited states and the subsequent decay of these inner-shell holes by the emission of a cascade of Auger electrons.}, year = {2019}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00039050}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 18906, author = {Hoff, D.}, title = {Elektronendynamik in fokussierten Einzelzyklenpulsen}, abstract = {This work investigates light-driven electron re-scattering from atomic gases and metal nanotips in focused few-cycle laser pulses. In particular, the work concentrates on the investigation of the evolution of the electric field of few-cycle pulses during focussing. Electrons emitted from a Tungsten nanotip are used to probe the electric field. With this insight the differences between the noble gas Xenon and nanotips made of Tungsten and Gold can be understood. To measure such fast processes, ultra-short laser pulses consisting of merely a few optical cycles (<2) are employed. When dealing with pulses as short as this, the relative position between the optical carrier wave and envelope becomes important. This value is called the carrier-envelope phase and is responsible for how the re-scattering takes place. Having control over this phase means being able to control the re-scattering process. As determining this value at the site of interaction is extremely difficult, measurements have been almost exclusively determining the “relative” carrier-envelope phase dependence, i.e. the effects of the change in carrier-envelope phase without an absolute reference. As examination of the phenomena investigated herein requires a knowledge of the “absolute” carrier-envelope phase, a method for determining this value is proposed and implemented. To this end, the phase dependencies of the photo-electron spectra of Xenon are compared to those of atomic Hydrogen, which can in turn be calibrated with ab initio calculations. This insight makes it possible to use the relatively easy determination of the carrier-envelope phase dependence of Xe-spectra as a ruler in other measurements. For instance, further photo electron spectra of Argon and Krypton are shown. Because the carrier-envelope phase shifts through the focus it is necessary to know these changes in order to understand local interactions. The metal nanotip, being an extremely localized electron emitter, serves splendidly as a tool to quantify the focussing of the electric field of few-cycle pulses. For the first time the carrier-envelope phase of a wide range of the focus, both on and off axis, was scanned without complications from volume averaging. Significant deviations from the often assumed arcustangent-shaped evolution described previously by Gouy on the optical axis for the monochromatic case were observed. The behaviour is well reproduced with an analytic model calculated by Porras and can be drawn back to the spectral geometry of the laser beam, which can be easily accessed experimentally and used for a coarse estimation of the focusing properties. The insight into the relationship between input beam properties and focussing behaviour allows for better interpretation and design of light-matter interactions in the future. Here, this technique is utilised to compare the absolute carrier-envelope phase dependence of electron re-scattering at metal nanotips, i.e. Tungsten and Gold, and in Noble gasses. We find that the observed shift can be attributed to the shape of the ionization potential of the different species and that in case of the nanotips the optical near-field due to the geometry of the tip causes an additional phase shift.}, year = {2019}, month = {5}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=574}, note = {papertype:d, rsaps:1, filetype:pdf, hij:0, public:1,} } @Thesis { 18701, author = {Luckner, P.}, title = {Entwicklung, Aufbau und Charakterisierung eines optischen, hochgenauen Target-Positioniersystems}, abstract = {Die Bachelorarbeit wurde am Institut f\{\"\{u\}\}r Optik und Quantenelektronik Jena erstellt. Die Arbeitsgruppe der relativistischen Laserphysik untersucht die Wechselwirkung hochintensiver Laserstrahlung mit Materie. Eines der aktuellen Projekte ist der Aufbau, die Entwicklung und die Anwendung des POLARIS-Lasersystems. POLARIS steht f\{\"\{u\}\}r Petawatt Optical Laser Amplifier for Radiation Intensive ExperimentS und ist das derzeit leistungsst\{\"\{a\}rkste, vollst\{\"\{a\}ndig dioden-gepumpte Hochleistungslasersystem der Welt mit Pulsspitzenleistungen von bis zu 170 TW. Hintergrund des POLARIS-Projektes ist zum einen die Entwicklung von dioden- gepumpten Lasersystemen und zum anderen die Untersuchung von lasergetriebenen Beschleunigungsmechanismen. Ziel der Bachelorarbeit ist die Entwicklung, der Aufbau und die Charakterisierung eines hochgenauen optischen Target-Positioniersystems f\{\"\{u\}\}r das Hochleistungslasersystem POLARIS. Aufgrund der sehr kleinen Fokusgr\{\"\{o\}\}\{\"\{s\}\}e, ist eine hochgenaue Positionierung der Targets notwendig. Das Target soll somit m\{\"\{o\}\}glichst pr\{\"\{a\}zise innerhalb der Rayleigh-L\{\"\{a\}nge des POLARIS Lasers positioniert werden. Hierf\{\"\{u\}\}r wird das Target mit einem Laser-basierten optischen Aufbau vermessen. Momentan erfolgt das Vermessen der Targets noch manuell durch einen Mitarbeiter, der vor jedem Experiment ca. zwei Stunden f\{\"\{u\}\}r diesen Vorgang ben\{\"\{o\}\}tigt. Um diesen Prozess nicht nur deutlich schneller, sondern auch genauer zu gestalten, soll dieser weitestgehend automatisiert werden. Zun\{\"\{a\}chst erfolgt in Kapitel 2 eine kurze Einf\{\"\{u\}\}hrung in die Grundlagen des POLARIS Lasers und es werden verschiedene Methoden der Positionsbestimmung und Bildverarbeitung diskutiert. In Kapitel 3 wird der optische Versuchsaufbau charakterisiert. Hierbei liegt der Schwerpunkt auf der Target-Positionierung und dem Wegl\{\"\{a\}ngenmesssystem. In Kapitel 4 wird das herausgearbeitete Konzept zum Autofokussystem n\{\"\{a\}her erl\{\"\{a\}utert und aufgetretene Probleme analysiert. Anschlie\{\"\{s\}\}end erfolgt die Umsetzung der Ans\{\"\{a\}tze, wo das Autofokussystem auf seine Genauigkeit und Reproduzierbarkeit \{\"\{u\}\}berpr\{\"\{u\}\}ft wird. In Kapitel 5 werden schlie\{\"\{s\}\}lich die Ergebnisse diskutiert und ein kurzer Ausblick gegeben. Die Idee ist, dass das Target - nach Eingabe weniger Parameter - vermessen und anschlie\{\"\{s\}\}end nach jedem Schuss positioniert werden soll. Hierzu wird \{\"\{u\}\}ber den selbst entwickelten Auto-Fokus eine Referenzstelle f\{\"\{u\}\}r den Laserfokus auf dem Target scharf gestellt und die zu beschie\{\"\{s\}\}enden Stellen mit einem konfokal-chromatischen Sensor entlang der optischen Achse vermessen.}, year = {2019}, month = {4}, school = {Ernst-Abbe-Hochschule Jena; Fachbereich Feinwerktechnik}, file_url = {t3://file?uid=587}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 18708, author = {Samsonova, Z.}, title = {Relativistic interaction of ultra-short laser pulses with nanostructured solids}, abstract = {Relativistic interaction of ultra-intense laser pulses with nanostructured solids is widely considered to be one of the most promising directions for research in high energy density physics. This thesis investigates the influence of the target morphology on the plasma parameters and produced hard X-ray emission. The study is rather broad and covering a range of emerging applications such as a development of efficient X-ray sources and generation of the extreme states of matter for laboratory astrophysics. We have performed a sequence of experimental campaigns starting from a benchmark experiment at moderate laser intensities and continuing with measurements at relativistic intensities (Iλ^2 ≥1.3 × 10^18 Wcm−2μm2). A set of fundamental questions regarding the laser energy absorption and morphology dependent plasma dynamics were addressed. Measurements of the bremsstrahlung emission and K-shell emission helped to draw some very important conclusions. First of all, nanowire targets are impractical for the generation of the cold line emission since they demonstrate essentially the same photon flux as the flat targets. However, according to the detected emission from the highly charged ion states (He- and H-like), nanowire morphology enables an effective generation of hot dense plasmas. Spectroscopic analysis of the produced X-ray emission, as the main diagnostic tool, revealed keV temperatures and solid density (≥10^23 cm−3) plasmas. In fact, such plasmas can be generated also with a planar target, however only in a thin top layer since the laser cannot deposit energy deeper. The use of NW arrays, on the other hand, increases the laser energy absorption and the interaction volume, resulting in an effective plasma heating, which does not take place for the flat targets. We have also experimentally observed higher flux and higher energies of the ions accelerated away from the front surface of the target matching with the other observations. The experimental results were supported by numerical simulations. For the chosencases, we have synthesized X-ray line spectra using the plasma parameters provided by the Particle-in-Cell (PIC) and Hydrodynamic (HD) simulations. A good correlation between the measured and synthetic spectra has been achieved. The plasma dynamics for the case of flat and nanostructured solids is strikingly different. For hot high-density plasmas, the collisional rates (e.g., ionization, excitation) are high and, therefore, radiative cooling of the plasmas may overrun hydrodynamic cooling, as it happens for nanowire targets. This naturally causes a great increase in the X-ray yield. The response of the flat and nanowire targets was investigated in the interaction with short- and long-wavelength laser pulses (0.4 μm and 3.9 μm), corresponding to completely different regimes of interaction. While ultra-short laser pulses in UV, visible and near-infrared are commonly used in laser-induced plasma studies, femtosecond mid-infrared pulses have not been yet extensively applied. In this thesis, we highlight the potential of such long-wavelength drivers to generate hot and dense plasmas. We demonstrate that this becomes feasible only with nanowire targets.}, year = {2019}, month = {3}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00038370}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 18608, author = {Wustelt, P.}, title = {Atome und Molek\{\"\{u\}\}le fundamentaler Bedeutung in intensiven Laserfeldern: He, He+ und HeH+}, abstract = {This work focuses the control of fundamental single- and two-electron systems using intense, ultra-short laser fields and includes new measurements, novel data evaluation techniques, and interpretation using various theoretical techniques. The measurements were carried out using an ion-beam apparatus that produces a beam of atomic or molecular ions, which is exposed to the controlling laser pulses causing fragmentation and/or ionization. The three-dimensional momenta of these fragments are then detected in coincidence, which allows for reconstruction of the interaction dynamics. In this thesis, to understand the fundamental timing of the laser-induced electron tunneling, the attoclock method was applied to the helium ion, a single-electron system with twice the charge of hydrogen. This serves to test and refine models of tunneling ionization and the larger intensity required for ionization enables the investigation of the tunneling process close to the ideal case - in the quasi-static tunnel regime. Evaluation of the measured electron-emission angle as a function of the radial momentum for He+ is significantly smaller than for, the typically used, atoms with lower ionization potential. Moreover, using He+ results in a much lower Keldysh parameter, which significantly reduces the importance of nonadiabatic effects that can complicate interpretation. The results are in good agreement with TDSE solutions as well as semiclassical simulations that do not include tunneling times. Further, double ionization of the helium atom by nearly circularly polarized few-cycle laser pulses was investigated. The dependence of the sequential double ionization on the subcycle shape of the ionizing few-cycle laser field was demonstrated by comparing measured ion momentum distributions with classical Monte Carlo simulations. Simulations based on a purely sequential ionization model show a remarkable good agreement with the experimental observations and reproduce the characteristic 6-peak structure of the measured ion momentum distribution after double ionization with few-cycle laser pulses. In addition to laser-induced ionization of fundamental atomic systems with strong laser fields, in this work the first experimental investigation of the simplest asymmetric molecule, the helium hydride ion, in strong laser fields was performed. Helium hydride is only stable as an ion and, therefore, an ion beam apparatus is required for its investigation. This study focused on how the asymmetric structure, and the resulting permanent dipole moment of the HeH+, influence laser-induced fragmentation. Both experiment and theory for dissociation, single ionization and double ionization of HeH+ and the isotopologue HeD+ reveal, that for the asymmetric molecule, direct vibrational excitation, with almost no electronic excitation as the initial process, dictates the fragmentation process. The dynamics of this extremely asymmetric molecule contrasts the symmetric molecules and gives new and fundamental insights into the behavior of molecular systems in general.}, year = {2019}, month = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00038372}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 18677, author = {Menz, E.}, title = {A Scintillation Particle Detector for Recombination Experiments at CRYRING@ESR}, abstract = {The following work describes the implementation of a single-particle detector based on a YAP:Ce scintillation crystal at the CRYRING heavy-ion storage ring at GSI. YAP:Ce is a durable and non-hygroscopic crystal that is bakeable to a certain degree and is thus suitable for installation directly in the ultra-high vacuum of the storage ring. The photons produced by the scintillator are detected by a photomultiplier tube. The detector is located downstream from a dipole magnet and is used to detect reaction products that undergo a change of their charge-to-mass ratio in the preceding straight section of the ring which houses the electron cooler. This positioning facilitates a number of applications for the setup that include the observation of beam losses both from interaction with residual gas atoms and molecules and with electrons in the cooler section. It can also be used for future recombination studies in the cooler section, providing detailed insight into the atomic structure of highly charged ions. The detector has been assembled and installed at CRYRING and was used during two beamtimes in August and November of 2018 to test its functionality and gather first experimental data. During these tests a number of issues concerning the detector itself and the signal read-out were identified and solved and the setup demonstrated its suitability for detecting single ions even at low energies of ∼300 keV. Moreover for the November beamtime a data acquisition system was implemented and tested.}, year = {2019}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=575}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 18592, author = {Bernhardt, H.}, title = {Hochpr\{\"\{a\}zise R\{\"\{o\}\}ntgenpolarimetrie mit Diamantkristallen}, abstract = {The dissertation describes the development and application of several diamond crystal x-ray polarizers. The polarizers are based on the channel-cut principle, in which an X-ray beam is diffracted several times under a Bragg angle of 45° and linearly polarized. The diamond crystals were characterized and the effect of defects (dislocations and stacking faults) on X-ray polarimetry were investigated. Since the diamonds were unsuitable for the fabrication of monolithic channel-cut crystals, special quasi-channel cuts (QCC's) out of invar alloy and mirror mounts were developed. With these QCC's up to four diamonds could be adjusted parallel to each other with a precision of sub-μrad. These diamond QCC’s were used in experiments at the European synchrotron in Grenobel, where an unprecedented polarization purity of 1.3 x 10^(-10) was achieved. As a further result, it was proved that the polarization purity is limited by the divergence of the synchrotron and that a better purity can be measured with reduced divergence. Thus, even better polarization purity can be achieved at x-ray sources with lower divergence, e.g. Synchrotron 4th generation and X-ray lasers. This is an important result for the measurement of vacuum birefringence in future. Al in al the dissertation shows that even diamond crystals with dislocation densities in the range of 10^4 to 10^6 cm^-2 are suitable for high-precision X-ray polarimetry and the production of highly pure linear polarized X-ray beams.}, year = {2019}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00038264}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Thesis { 18702, author = {Arndt, B.}, title = {Time-of-flight Measurements at HILITE}, abstract = {-}, year = {2018}, month = {12}, school = {Johann Wolfgang Goethe-Universit\{\"\{a\}t Frankfurt; Fachbereich Physik}, file_url = {t3://file?uid=570}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 18928, author = {Massinger, A.}, title = {Aufbau und Charakterisierung eines zeitaufgel\{\"\{o\}\}sten 2D Plasma Anrege-Abfrage-Systems}, abstract = {Im Rahmen dieser Arbeit wurde ein Anrege-Abfrage-System mit zwei Probepulsen entwickelt. Mithilfe dieses Systems kann ein Plasma, das dem Vorplasma des Polaris-Lasers gleicht, erzeugt und untersucht werden. Das Vorplasma besitzt einen wichtigen Einfluss auf die Effizienz der TNSA Laser- Protonenbeschleunigung. Da das diese Prozesse auf sehr kurzen Zeitskalen von ca. 1 ps stattfinden, muss der Aufbau eine vergleichbare zeitliche Aufl\{\"\{o\}\}sung bieten. Dies ist Elektronisch nicht m\{\"\{o\}\}glich. Daf\{\"\{u\}\}r wurde eine rein optisches System zur zeitlichen Separation eines Pulses in mehrere Einzelpuse entwickelt, das Pulse mit einer Pulsdauer von 400 fs und einen zeitlichen Versatz zwischen 0 ps und 333 ps mit einer Genauigkeit von 67ps erzeugt.}, year = {2018}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=569}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 18289, author = {Fuchs, S.}, title = {Optische Koh\{\"\{a\}renztomographie mit extrem ultravioletter Strahlung}, abstract = {In this thesis, the concept and the realization of laboratory-based optical coherence tomography in the extreme ultraviolet (XUV) spectral range is presented. XUV coherence tomography (XCT) is a three-dimensional imaging technique with an axial resolution down to a few nanometer. A theoretical XCT model has been developed for the reconstruction of the sample structure, which includes the interaction between the XUV light and the sample. It is valid for absorbing samples illuminated under arbitrary angles of incidence and thus extends a common model of optical coherence tomography (OCT). As the information about the absorption and dispersion of the sample is contained in the XCT model, an additional reconstruction of material properties of the sample will be enabled. The demonstration of laboratory-based XCT, which before has only been implemented at synchrotron facilities, was a major gaol of this thesis. Using high harmonic generation (HHG) of a femtosecond infrared laser pulse, a broadband laboratory-based XUV source with sufficient photon flux (approximately 0,2 nW/eV over the full bandwidth) in the so-called silicon transmission window between 30 eV − 100 eV was realized. A revised XCT microscope has been designed, constructed and adapted to the new laser-based XUV source, which routinely facilitates XCT measurements in the laboratory. The microscope is a three meter long vacuum beamline consisting of XUV source, focusing mirror, and sample chamber. A comparison between laser-based and synchrotron-based measurements shows good agreement. With laser-based XCT, an axial resolution of approximately 30 nm has been achieved. This is comparable to the achieved synchrotron-based axial resolution of approximately 20 nm. Accordingly, the axial resolution of XCT is 2-3 orders of magnitude higher than in conventional OCT. Unlike conventional OCT, the realized XCT setup does not use a beamsplitter for the generation of a reference wave. Instead, the surface of the sample serves as a reference. Therefore, the interferometric stability is intrinsically achieved and simplifies the experimental setup significantly. However, such a setup has the disadvantage that the reconstruction is ambiguous, since autocorrelation artifacts appear. A non-ambiguous reconstruction of the axial structure was so far not possible. In this thesis, a novel one-dimensional phase-retrieval algorithm is presented, which is able to remove the artifacts from the signal and allows a non-ambiguous reconstruction of the structure. Three-dimensional structured silicon-based samples have been investigated and processed with the new algorithm, which is referred to as PR-XCT. With the removal of artifacts and thus the possibility to use XCT on samples, whose inner structure is unknown before the measurement, a further goal of this thesis was achieved. In fact, during laser-based PR-XCT measurements, an unexpected nanometer-thin layer was found inside the sample, which was not intentionally planned in the production process. The existence of this layer and thus the XCT measurement could only be confirmed by a transmission electron microscope. To this end, a thin slice was cut out of the sample, which was thus destroyed. The resolution of a scanning electron microscope was not high enough to resolve the layer. Later it turned out, that the vacuum chamber was vented for a short amount of time during the production process and a 1-2 nm layer of SiO2 was formed. Hereby, a striking advantage of XUV microscopy becomes apparent. Lighter elements like oxygen produce a high contrast in the XUV albeit they are almost indistinguishable from surrounding light elements like silicon in an electron microscope. In this work, XCT is realized using optics with low numerical aperture (NA) since the fabrication of high NA optics in the XUV is technically extremely demanding. Therefore, the lateral resolution of the laboratory-based XCT setup is limited to approximately 23 μm. At least, the lateral resolution has been improved by a factor of 10 compared to the synchrotron-based measurements. However, the axial resolution of XCT is still orders of magnitudes better than the lateral resolution. Even with this technical limitation of the current XCT setup, several applications are within reach, e.g., threedimensional investigation of (multilayer-)coatings of optical mirrors or even XUV-mirrors, axial structured devices like solar cells or axial-structured semiconductor devices like graphene-based electronics. In addition, imaging of laterally homogeneous biological membranes might be possible. XCT with high numerical aperture and thus high lateral resolution could even have further applications, e.g., non-destructive three-dimensional imaging of semiconductor devices, lithographic masks, and biological structures. A combination of XCT with lensless imaging techniques like „Coherent Diffraction Imaging“ or Ptychography might be a promising approach to improve the lateral resolution of XCT. Furthermore, the intrinsic time resolution of the HHG source in the range of femto- or even attoseconds may allow time-resolved imaging of ultrafast processes in solids.}, year = {2018}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00037866}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 18926, author = {Irshad, F.}, title = {Single-Shot Optical Probing of Laser-Generated Plasmas}, abstract = {TNSA process is an important means to generate energetic ion beams. The understanding of the pre-plasma is an important step towards optimizing the TNSA process. In this work, a complete system to generate and characterize different kinds of plasma was assembled. Generating two pulses and using them to probe the plasma in a single shot increases the utility of such a step since it eliminates the shot to shot variations. Different absorption mechanisms were considered while investigating the plasma and their dominance evaluated in the context of current work. Two devices named temporal separation and spatial separation devices were used to generate the probe pulses. An imaging system to focus, collect and relay the pulses at a large distance was built and optimized to generate near diffraction limited spatial resolution (≈3.5μm). The pulses also give a sufficient temporal resolution with 330 fs pulses to study the hydrodynamic evolution of the plasma. The plasma was created with pulses ranging in intensity from 0.67E16 to 3E16 W/cm^2 with a pulse duration of 120 fs at a central wavelength of 1.03 μm. An intensity as well as a time scan was done to evaluate the plasma based on the scale lengths and plasma electron temperature. Both linear and circular polarization of pump pulse was used to create the plasma. A custom LABVIEW program was used to analyze the phase and generate scale lengths from it by Fourier transform. To gain access to the 3-D information, a cylindrical symmetry was assumed, and Abel inversion was applied on the 2-D chord phase integrals. From this, plasma scale lengths were calculated, and utilizing the single-shot pulses at different time steps, plasma velocity and plasma electron temperatures were calculated. Both the linear and circular polarized pump pulses generated plasma scale lengths in the range of 4-10 μm with an electron temperature of 50-280 eV. This data was also compared with MULTI-fs simulation data and possible reasons of deviations discussed. Dominant absorption mechanisms identified are the Normal and Anomalous Skin Effects under normal incidence. The similarity in the plasma scale lengths and the plasma electron temperature for both polarization implies the absence of vacuum heating and resonance absorption. This is also confirmed by underlying physics of these two absorption processes, which require an electric field component in the direction of the plasma electron gradients.}, year = {2018}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=573}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 18325, author = {Reuter, M.}, title = {Characterisation of a Laser Wakefield Accelerator with Ultra-Short Probe Pulses}, abstract = {Within the frame of this thesis, aspects of the acceleration of electrons with high-intensity laser pulses inside an underdense plasma were investigated. The basic acceleration mechanism, which is referred to as laser wakefield acceleration relies on the generation of a plasma wave by an intense laser pulse. Since the plasma wave co-propagates with the laser pulse, its longitudinally alternating electric field moves with a velocity close to the speed of light and electrons trapped in the accelerating phase of the wave can be accelerated to relativistic energies. While basic principles such as the generation of a plasma wave, the injection of electrons into the accelerating phase of the wave and limits to the acceleration process are known, the exact processes occurring during the nonlinear interaction of laser pulse and plasma wave still need to be explored in more detail. The consequence of those nonlinear processes is a drastic change of the electron parameters – e.g. final electron energy, bandwidth and pointing – through slight changes in the initial conditions. In this context, the position in the plasma at which electrons are injected into the plasma wave plays a key role for the maximum achievable electron energy. Therefore, the injection of electrons at a defined position is a possibility to reduce shot-to-shot fluctuations and might make the electron pulses applicable, e.g. as a stable source of secondary radiation for temporally and spatially highly resolving imaging techniques. The investigation of controlled injection of electrons at an electron density transition demonstrated a correlation of electron pulse parameters such as electron energy gain and accelerated charge to the properties of the transition, and thus, might be a promising method to generate custom designed electron pulses. Nevertheless, shot-to-shot fluctuations in the electron parameters were still observed and are most likely caused by the nonlinear evolution of the laser pulse inside the plasma. To further reduce instabilities, deeper insight into these nonlinear processes is required and hence, a method to observe the plasma wave and the laser pulse. Combining an ultra short probe pulse with a highly resolving imaging system as successfully implemented at the institute of Optics and Quantumelectronics in Jena, more light can be shed on these processes, which take place on femtosecond and micrometer scales. With that system, characteristics of the magnetic fields inextricably connected to the acceleration process could be studied in unprecedented detail. This deeper insight allowed to observe signatures of the magnetic field of the driving laser pulse for the first time, which paves the way for the indirect observation of the main laser pulse during the interaction.}, year = {2018}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00038073}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17974, author = {Peshkov, A.}, title = {Interaction of atoms with twisted light}, abstract = {Twisted photons are particles which carry a nonzero projection of the orbital angular momentum onto their propagation direction. During the last years, the interaction between twisted photons and atoms became an active area of fundamental and applied research. In the present work, we show how the “twistedness” of Bessel and Laguerre-Gauss photons may affect a number of fundamental light-matter interaction processes in comparison with the results for standard plane-wave radiation. In particular, we perform an analysis of the photoionization of hydrogen molecular ions by twisted photons. It is shown that the oscillations in the angular and energy distributions of photoelectrons are affected by the intensity profile of twisted photons. We also investigate the excitation of atoms by these twisted photons. We demonstrate here that the orbital angular momentum of light leads to the alignment or specific magnetic sublevel population of excited atoms. Apart from these studies, we explore the elastic Rayleigh scattering of twisted photons by hydrogenlike ions. Our results indicate that the “twistedness” of incident photons may significantly influence the polarization properties of scattered light.}, year = {2018}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00034975}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 17964, author = {Kr\{\"\{o\}\}ger, F.}, title = {Charge State Tailoring for Relativistic Heavy Ion Beams}, abstract = {In this work charge state distributions of heavy ions have been calculated for the production of effective stripper foils for heavy ion acceleration facilities. In this context, the FAIR facility at GSI and the proposed Gamma Factory at CERN are presented, where the use of partially stripped, relativistic ions will be of special interest for upcoming experiments. To determine the charge state distribution as a function of penetration depth, various programmes have been applied, depending on the respective energy regime. For stripping scenarios in the lower energy regime, the GLOBAL code was applied, that allows to take into account up to twenty-eight projectile electrons for energies up to 2000 MeV/u. Since the GSI/FAIR facility can accelerate even low-charged uranium ions up to 2700 MeV/u, and the Gamma Factory at CERN considers a stripping scenario at 5900 MeV/u, another programme was needed. This is why for the stripping scenarios in the high energy regime, first the well-known CHARGE code was used. However, even though it can operate in the very high energy regime, it only takes into account bare, hydrogen- and heliumlike projectile charge states. To overcome this limitation, the recently developed BREIT code was verified and used for stripping scenarios in the high energy regime. As this code has no built-in treatment of the various charge-changing processes, it needs a multitude of information about the electron capture and loss cross sections as input parameters. Thus, for the calculation of charge state distributions with the BREIT code, cross sections were computed by well-tested theories and codes. The BREIT code together with the codes for the cross section computation were then applied for two studies: first for an exemplification study for the upcoming GSI/FAIR facility to show the practicability of the BREIT code together with the cross section programmes, and then for a study to find optimal stripper foils for the Gamma Factory study group at the CERN facility, in order to efficiently produce Pb⁸⁰⁺ and Pb⁸¹⁺ ions from a Pb⁵⁴⁺ beam before entering the LHC. Furthermore, experimental data of a beam time at ESR at GSI in 2016 was analysed, where a Xe⁵⁴⁺ ion beam of several MeV/u was colliding with a hydrogen gas target. The data allowed the derivation of experimental NRC cross sections, and it was shown that the predictions of the EIKONAL code are in good agreement with these cross sections in an energy range most relevant for upcoming experiments at CRYRING@GSI.}, year = {2018}, month = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=576}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 17860, author = {Kuschel, S.}, title = {Erzeugung dichter Elektronenpulse mit Laser-Plasma-Beschleunigern f\{\"\{u\}\}r QED-Experimente in hohen Feldern}, abstract = {Quantum electrodynamics (QED) is widely considered to be one of the most accurately tested theories. Nevertheless fundamental processes such as pair production from the vacuum or the motion of the electron in extreme fields have not been measured in the laboratory to date. Their measurement requires a high intensity laser together with a high intensity electron or γ-beam, which can be produced by a high density electron bunch. A recent development within the last two decades are plasma based accelerators. The high fields that can be sustained by a plasma are used to deliver extremely short and dense electron bunches while shrinking size and costs of the device. Importantly, they are automatically co-located with and synchronized to a high intensity laser pulse, providing an ideal basis for investigating QED in high fields.The availability of generating dense electron bunches brings new QED experiments within reach. However, the quality and stability of laser wake field accelerated (LWFA) electron beams still has to be improved to make these experiments possible. Beyond the tests of QED, the stability and quality of the electron beam is also crucial for highly demanding applications such as LWFA-driven free-electron lasers. The first part of this thesis is devoted to the LWFA process and its improvements with a particular emphasis on improving the stability of laser plasma accelerators. It is shown that the gas dynamics on a 10 μm scale plays an important role in LWFA, which has not been fully appreciated yet. Density modulations on a 10 μm scale were measured in a gas jet using a few-cycle probe pulse. It is shown that self-injection can be triggered by these modulations. Particle-in-cell (PIC) simulations and analytical modeling confirm the experimental results. A gas cell providing a homogeneous plasma density has been developed in order to reduce self-injection. Using this gas cell, it was possible to suppress self-injection. The experiments show that self-injection was suppressed in the gas cell. Using ionization injection and the gas cell, the beam shape as well as the pointing stability were strongly improved. This finding paves the way towards self-injection free acceleration in a plasma based accelerator. It also establishes a new requirement on the homogenouity of the plasma density – not only for LWFA, but also in a broader context, for example in particle driven plasma wake field acceleration (PWFA). In the second part of this, the possibility of focusing the ultra-short electron bunch by passive plasma lensing is studied. LWFA-beams typically have a very small source size and a divergence of the order or a few mrad, resulting in a rapid drop in electron beam density during free-space propagation. Many of the envisioned experiments, however, require intense focused electron bunches. Therefore, the concept of passive plasma lensing has been applied to ultra-short LWFA-bunches for the first time. The passive plasma lens effect was demonstrated experimentally by using a second gas target with predefined density. PIC simulations and analytical modeling describe the measured effect. Notably, the observed focusing strength of the passive plasma lens is larger compared to a conventional magnetic quadrupole lens. The analytical model predicts that the focusing strength can be further enhanced by increasing the bunch charge.}, year = {2018}, month = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00034353}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17643, author = {Arunchalam, A. K.}, title = {Investigation of laser-plasma interactions at near-critical densities}, abstract = {During the high-intensity laser-plasma experiments conducted at the high-power laser system JETI40 at IOQ, the two qualitatively different laser side-scattering processes have been observed. The side-scattering observed during the first experiment was found to be non-symmetric in nature with respect to the laser’s propagation direction and it was estimated to occur from under-dense to quarter critical plasma densities. The scattering angle was found to gradually decrease, as the laser pulse propagates towards regions of higher densities (i.e. the gas jet centre). For increasing nozzle backing pressures, the scattering was also found to gradually change from upward to downward directions. In this thesis, this side-scattering process is shown to a consequence of the laser propagation in non-uniform plasma, where the scattering angle was found to be oriented along the direction of the plasma gradient. In the second experiment, a symmetric side-scattering process with respect to the laser’s propagation direction was observed from the intense central laser-plasma interaction region. This scattering process was found to originate from a longitudinally narrow laser-plasma interaction region and vary over +-50° with respect to the laser’s transverse direction. It was found to primarily occur in the nearcritical plasma density regime (0.09 n\_c to 0.25\_nc, where n\_c is the plasma critical density). In contrast to the previous experiment, Raman scattering has been shown to be the cause of this symmetric scattering process, where the scattering occurs as the result of the wave vector non-alignment between the main laser pulse and the resulting plasma wave.}, year = {2017}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00034772}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 17823, author = {Pf\{\"\{a\}fflein, P.}, title = {Entwicklung und Aufbau eines Teilchendetektors f\{\"\{u\}\}r erste Experimente am Ionenspeicherring CRYRING}, abstract = {This thesis describes the development of a particle counter based on a Cerium activated yttrium aluminium perovskite (YAP:Ce) scintillator. The detector is designed for charge exchange experiments at the ion storage ring CRYRING at the GSI Helmholtz Zentrum f\{\"\{u\}\}r Schwerionenforschung in Darmstadt. It will be used for charge exchange experiments. The suggested detector design was tailored for the requirements set by the desired ultra-high vacuum conditions of up to 1E-12 mbar at CRYRING in combination with a high radiation hardness against ion irradiation. The design was kept as simple as possible, offering an easy exchange of the scintillator (not limited to YAP:Ce) if necessary. For an estimation of the detector lifetime the radiation hardness was systematically investigated for hydrogen, oxygen and iodine irradiation in the energy regime of 1–10 MeV. The measurement took place at the JULIA tandem accelerator operated by the Institute of Solid State Physics at the University of Jena. As the measurement of detector degradation the light yield was used. Values determined for the critical fluence, defined as fluence at half the initial light yield, varied from 1E15/cm2 in the case of hydrogen down to 1.7E12/cm2 for iodine irradiation. Prior to the hardness investigation, the used photomultiplier tube (PMT) was tested for temporal drifts of the output signal and whether the signal depends on the position of illumination on the sensitive surface. To the limit of the experimental uncertainties, no such dependencies could be observed. It was concluded that the investigated PMT was well suited for the use in the experiment as well as in the particle counter.}, year = {2017}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=590}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 17551, author = {Kienel, M.}, title = {Power Scaling of Ultrashort Pulses by Spatial and Temporal Coherent Combining}, abstract = {Ytterbium-doped solid-state lasers are versatile tools for the generation of intense ultrashort pulses, which are the key for many industrial and scientific applications. The performance requirements on the driving laser have become very demanding. High pulse-peak powers and high average powers are desired at the same time, e.g. to initiate a physical process of interest while providing fast data-acquisition times. Although sophisticated state-of-the-art laser concepts have already demonstrated remarkable performance figures, their working principles hamper the simultaneous delivery of both high peak power and high average power. Coherent combination of pulses provided by an amplifier array constitutes a novel concept for scaling both the average power and the peak power. Although this technique is applicable to any laser concept, it is especially well suited for fibers due to their high single-pass gain and their reproducible, excellent beam quality. As the number of amplifier channels may become too large for the ambitious energy levels being targeted, divided-pulse amplification (DPA) – the coherent combination of a pulse burst into a single pulse – can be applied as another energy-scaling approach, which is the focus of this thesis. In this regard, the energy-scalability of DPA implementations as an extension to well established chirped-pulse amplification (CPA) is analyzed. In a first experiment, high-energy operation is demonstrated using an actively-controlled DPA implementation and challenges that occurred are discussed. Next, in a proof-of-principle experiment, the potential of merging spatial and temporal coherent combining concepts in a power- and energy-scalable architecture has been demonstrated. Furthermore, phase stabilization of actively-controlled temporal and spatio-temporal combination implementations is investigated. Based on the findings, the layout of a state-of-the-art high-power fiber-CPA system is improved and extended by eight parallel main-amplifier channels, in which bursts of up to four pulse replicas are amplified that are eventually stacked into a single pulse. With this technique < 300 fs pulses of 12 mJ pulse energy at 700 W average power have been achieved, which is an order of magnitude improvement in both energy and average power compared to the state-of-the-art at the beginning of this work.}, year = {2017}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00033668}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17464, author = {M\{\"\{o\}\}ller, M.}, title = {Probing Strong-field Photoionization of Atoms and Diatomic Molecules with Short-wave Infrared Radiation}, abstract = {The availability of pico- and femtosecond laser pulses, which can be focused to peak intensities in the range between 10^12 and 10^16 W/cm2, allows the investigation of the interaction between atoms or diatomic molecules with strong laser fields. It has revealed fascinating phenomena such as above-threshold ionization (ATI), high energy above-threshold ionization (HATI), non-sequential ionization (NSDI), high-harmonic generation (HHG) and, most recently, frustrated tunnel ionization (FTI). Today, these characteristic strong-field phenomena are the backbone of the burgeoning field of attosecond science. Derived applications presently mature to standard techniques in the field of ultrafast atomic and molecular dynamics. Examples are HHG as table-top source of coherent extreme ultraviolet radiation with attosecond duration or the application of HATI for the characterization of few-cycle laser pulses. Although experimental and theoretical considerations have shown that using longer laser wavelength is interesting for applications as well as for fundamental aspects, primary due to technological limitations, the vast majority of measurements has been performed at laser wavelengths below 1.0 μm. In this thesis, an optic parametric amplification laser source of intense femtosecond laser pulses with short-wave infrared (SWIR) and infrared (IR) wavelength is put to operation, characterized and compressed to intense few-cycle pulses. Further, it is applied to investigate strong-field photoionization (SFI) of atoms and diatomic molecules using two different experimental techniques for momentum spectroscopy of laser-induced fragmentation processes. For SFI of atoms, the velocity map imaging technique is used to measure three-dimensional momentum distributions from strong-field photoionization of Xenon by strong SWIR fields with different pulse duration. Besides observation of the pulse duration dependence of characteristic features, like the low-energy structures, which are particularly pronounced in the SWIR, an eye-catching off-axis low-energy feature, called the “fork”, which appears close to right angle to the polarization axis of the laser, is investigated in detail. The corresponding modeling with an improved version of the semi-classical model, demonstrates that on- and off-axis low-energy features can be traced to rescattering between the laser-driven photoelectron and the remaining ion. They can, thus, be understood on the same footing as HATI, where the electron scatters into high energy states. SFI of diatomic molecules is investigated using an apparatus for Ion Target Recoil Ion Momentum Spectroscopy (ITRIMS). Besides measuring intensity dependent vector momentum distributions of the protons from SFI of the hydrogen molecular ion, it is shown that momentum conservation can be used to extract the correlated electron momentum from the measured data, although the electron is not detected. The capability of having experimental access to the momenta of all fragments, i.e. two protons and one electron, enables the analysis of correlated electron-nuclear momentum distributions. Together, with a one-dimensional two-level model, this sheds light on correlated electron-nuclear ionization dynamics during SFI of diatomic molecules by SWIR fields.}, year = {2017}, month = {8}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00033538}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17471, author = {Ullmann, J.}, title = {Laserspektroskopie an hochgeladenen Bismutionen zum Test der Quantenelektrodynamik}, abstract = {Ths dissertation concerns a test of the theory of quantum electrodynamics in strong fields by laser spectroscopy of the ground state hyperfine splitting of highly charged bismuth ions. The experiment was performed and analyzed at the storage ring ESR at Helmholtzzentrum f\{\"\{u\}\}r Schwerionenforschung in Darmstadt. A systematic study of space charge effects was carried out and the laser wavelength measurement was verified by absorption spectroscopy of iodine. The determination of the ion velocity by an in-situ measurement of the electron cooler voltage reduced the main systematic uncertainty of the previous experiment by over an order of magnitude. This indicated the necessity to establish a permanent high voltage measurement at the electron cooler, which was promoted in this work. The measured wavelengths were combined in a specific difference which deviates significantly from the theoretical predictions. None of the investigated systematics has the magnitude to explain this deviation. Apart from doubts regarding theory, the literature value of the nuclear magnetic moment of Bismuth-209 is indicated as a possible explanation. Follow-up experiments to solve this puzzle are described in the outook.}, year = {2017}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00033497}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 18020, author = {Keppler, S.}, title = {R\{\"\{a\}umlich-zeitliche Optimierung der Laserimpulse Yb3+-basierter Hochleistungs-Lasersysteme}, abstract = {As an alternative to established laser systems, directly diode-pumped petawatt systems based on Yb3+-doped laser materials are being developed, which can generate pulse energies of > 100 J as well as pulse durations of < 100 fs. The use of narrow-band high-power laser diodes as pump light sources allows an efficient excitation of the laser material, which significantly increases the repetition rate. For the successful application of these laser systems in experiments, however, they must be optimized both spatially and temporally with regard to the required experimental parameters. A maximum focused peak intensity and the highest possible temporal intensity contrast are of particular importance here. In the context of this thesis the possibilities for the spatio-temporal optimization of the pulses of Yb³⁺-based laser systems are investigated. Firstly, the effect of the spectral properties of Yb³⁺-doped materials on the amplified spectrum of laser pulses is investigated and optimized by the development of special spectral transmission filters, which results in an increased bandwidth and thus a reduction of the pulse duration. On the other hand, the spatial optimization of the laser pulse amplification is presented, whereby first the influences of the spatial amplification profile and the pump-induced phase aberrations are investigated. The optimization is then demonstrated by the development of a novel imaging amplifier architecture. Finally, the optimization of the temporal intensity contrast is presented. Newly developed methods have made it possible to completely avoid intensive pre-pulses. A detailed analysis of the generation of spontaneous amplified emissions in high-power laser systems is also derived. For the first time, the analytical model enables a comprehensive conceptual design of high-contrast laser systems with high peak powers.}, year = {2017}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00033553}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Phdthesis { 17916, author = {Landgraf, B.}, title = {Stimulated Raman backscattering in transient laser generated plasmas with ultra-short seed pulses}, abstract = {Stimulated Raman backscattering (SRBS) is a promising concept to create ultra-intense laser pulses. State-of-the-art SRBS experiments find best conditions close to the Langmuir wave-breaking limit, which is one reason, why it cannot be applied at high energy class systems, as focal lengths of hundreds of meters would be necessary. A solution is offered, if the scheme can be transferred to high pump intensities in the strong wave-breaking regime. One of the dominant competitors of SRBS at high intensities is Langmuir wave-breaking, which increases significantly at 10^14 W/cm^2. Recent studies propose the existence of a time frame in which wave-breaking starts, but is too slow to dephase the electron distribution resulting in efficient amplification with ultra-short seed pulses. In this work SRBS, in transient plasma distributions is demonstrated leading to broadband amplification of up to 80 nm. To understand the temporal dynamics, particle in cell (PIC) simulations are performed. The highest conversion efficiency of up to 1.2 {\%} is found at 5 x 10^15 W/cm^2, which corresponds to the strong wave-breaking regime. At even higher intensities efficiency drops again, resulting in a lower average efficiency, but conserving its transform limited pulse duration. After wave-breaking at high intensities a decrease of the pulse energy is observed. To minimize this effect \$\mu\$m-sized nozzle orifices are manufactured for perfect matching between overlap length and plasma dimension achieving the best conversion efficiency of 2.3 {\%} in this work. To explore static linear density gradients, trapezoid shaped nozzle orifices are sintered by a 3D printer. They provide exceptional stability and an SRBS spectrum of up to 30 nm bandwidth, which should only be accessible in the non-linear case. PIC simulations agree very well with negative density gradients (pump frame), which can partly compensate the pump chirp. Spectral features in the PIC simulation related to the absence of wave-breaking are not observed, possibly pointing to higher dimensional effects. There is no agreement of 1D PIC simulations and positive gradients in two consecutive experiments, which reinforces the thesis, that higher dimensional PIC simulations are necessary. One candidate for two dimensional mechanisms limiting SRBS efficiency is identified as angular chirp whose influence is extrapolated. This potentially allows the conversion efficiency to be increased by a factor of two. By inserting two glass wedges inside the seed setup, it is possible to change the pulse duration by dispersion. A strong correlation between efficiency function and pulse duration is found, where the former oscillates with the plasma period. This important feature has consequences for future experiments trying to explore the coherent wave breaking regime as it is not only necessary to achieve a sufficient growth time, but now also higher plasma densities are necessary for sub-20 fs seed pulses.}, year = {2017}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://suche.thulb.uni-jena.de/Record/893532339}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17231, author = {Wu, Z.}, title = {Angular Correlation and Polarization of X-rays Emitted from Highly Charged Ions}, abstract = {In collisions of highly charged ions with electrons or light, ions are usually excited to one of their excited states and, then, may stabilize radiatively under the emission of fluorescence photons. Detailed studies on the emitted photons can help understand the structure and collision dynamics of the ions. When compared with total decay rates, angle-resolved properties such as angular correlation and polarization of emitted photons were found more sensitive to various interactions and effects and, actually, have helped provide new insights into electron-electron and electron-photon interactions in the presence of strong Coulomb fields. For this reason, such kind of studies has attracted considerable interest in both theory and experiment. Until now, however, almost all studies of x-ray angular correlation and polarization were performed for photons emitted from well-isolated energy levels. Little attention was paid so far to photon emissions from two or more overlapping resonances of ions. In this thesis, we develop a novel theoretical formalism to study radiative decay from the overlapping resonances. Special attention is paid to the question of how the splitting of these resonances affect the angular and polarization properties of emitted photons. Calculations are performed based on the density matrix theory and multi-configuration Dirac-Fock method. The obtained results from several case studies show that the photon angular distribution and polarization are strongly affected by the splitting and sequence of the overlapping resonances. Therefore, we suggest that accurate angle-resolved measurements of photon emissions may serve as a tool to identify level splitting and sequence of overlapping resonances in excited highly charged ions, even if they cannot be spectroscopically resolved. When applied to the isotopes with non-zero nuclear spin, moreover, such a tool can also be used to determine hyperfine splitting and associated nuclear parameters.}, year = {2017}, month = {5}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00032430}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17301, author = {Marx-Glowna, B.}, title = {Hochaufl\{\"\{o\}\}sende R\{\"\{o\}\}ntgenpolarimetrie}, abstract = {Polarimetry has a long history with versatile applications in chemistry and pharmacy in the visible spectral range. In the field of X-ray radiation, the interest in high-resolution polarimeters has only increased in recent years. This work is based on a project aiming to observe the vacuum birefringence in an ultra-intense laser field. The present dissertation describes the development of a precision polarimeter based on multiple reflections at a Bragg angle of 45° in silicon channel-cut crystals. A degree of polarization purity of 10^-10 could be achieved. This improves the best x-ray polarimeters to date by more than two orders of magnitude. In this thesis, experimental and theoretical factors are investigated, which currently limit the degree of polarization purity of precision polarimeters, such as multiple-beam cases, surface treatment of the crystals and source parameters. A new methodology of thin crystals is presented with which the degree of polarization purity can be improved in the future. The high purity of the precision polarimeter allows numerous new applications in nuclear resonant scattering and quantum optics as well as the characterization of X-ray sources of the 3rd and 4th generation.}, year = {2017}, month = {5}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00032505}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Mastersthesis { 17241, author = {Stock, S.}, title = {Auger cascades in resonantly excited neon}, abstract = {The Auger cascades following the resonant 1s -> 3p and 1s -> 4p excitation of neutral neon are studied theoretically. In order to accurately predict Auger electron spectra, shake probabilities, ion yields, and the population of final states, the complete cascade of decays from neutral to doubly-ionized neon is simulated bymeans of extensive MCDF calculations. Experimentally known values for the energy levels of neutral, singly and doubly ionized neon are utilized in order to further improve the simulated spectra. The obtained results are compared to experimental findings. For the most part, quite good agreement between theory and experiment is found. However, for the lifetime widths of certain energy levels of Ne+, larger differences between the calculated values and the experiment are found. It is presumed that these discrepancies originate from the approximations that are utilized in the calculations of the Auger amplitudes.}, year = {2017}, month = {3}, DOI = {10.1103/PhysRevA.95.053407}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=592}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 17021, author = {Seegert, N.}, title = {Signatures of the quantum vacuum in inhomogeneous electromagentic fields}, abstract = {According to the theory of quantum electrodynamics, zero-point fluctuations of the vacuum manifest themselves through the ubiquitous creation and annihilation of virtual electron-positron pairs. These give rise to classically forbidden nonlinear interactions between strong electromagnetic fields in vacuum, first described by Heisenberg and Euler in 1936. As these interactions only become sizable for large strengths of the involved fields, an experimental verification of purely optical signatures of the quantum vacuum nonlinearity is yet to be achieved. This thesis deals with various signatures of the quantum vacuum nonlinearity in the presence of inhomogeneous electromagnetic fields, putting emphasis on analytical methods. The proper treatment of inhomogeneities is motivated by the rapid development of high-intensity lasers capable of generating enormous field strengths in their focal spot, making them promising tools for upcoming discovery experiments. In the first part of this work we introduce “quantum reflection” as a new signature of the quantum vacuum nonlinearity, requiring manifestly inhomogeneous pump fields. To this end we start with an analytical expression of the “two-photon” polarization tensor (photon two-point function) in constant pump fields, and develop a formalism to generalize it to inhomogeneous pump fields. In the experimentally relevant weakfield limit our formalism permits a detailed study of various types of inhomogeneities and configurations. Additionally, we also gain insight into the nonperturbative strongfield limit. The investigation of quantum reflection is concluded by giving estimates for the attainable number of quantum reflected photons in experiments consisting of state-of-the-art high-intensity lasers. We then turn to the investigation of photon splitting and merging in inhomogeneous pump fields. For the first time, we compute the “three-photon” polarization tensor for slowly-varying but otherwise arbitrary pump field inhomogeneities in the low-energy limit. With its help we discuss in detail the polarization properties and selection rules governing these two processes. For photon merging we perform an elaborate study of possible experimental set-ups employing parameters of present-day state-of-the-art high-intensity lasers. The combination of polarization shifts, frequency conversion and the emission of the signal into background-free areas establishes photon merging as an ideal candidate to experimentally verify the nonlinear nature of the quantum vacuum in upcoming experiments.}, year = {2017}, month = {2}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00031968}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 16874, author = {Gassner, T.}, title = {High Precision X-Ray Spectroscopy of Highly Charged Heavy Ions}, abstract = {In the present thesis, the advantages of two new and complementary detector concepts for x-ray spectroscopy of highly charged ions over conventional semiconductor detectors have been worked out. These two detectors are the twin crystal spectrometer FOCAL and the metallic magnetic microcalorimeter maXs. Although the maXs microcalorimeter is still under development, first very promising x-ray spectra could be recorded at the ESR storage ring at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt. With the crystal spectrometer FOCAL, which was fully equipped for the first time, a dedicated beam time at the ESR, aiming for the precise determination of the 1s Lamb shift of hydrogen-like gold (Au^78+), could be conducted. The obtained result for the Lyman-a1 transition energy is afflicted with a small statistical uncertainty, however, the encountered systematic effects are still posing a challenge to overcome. In the outlook, it will be discussed in detail how the accuracy of a future measurement could be improved, and in which way both detector concepts could support each other optimally.}, year = {2016}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00031352}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 16972, author = {Tamer, I.}, title = {Investigation of Pump-Induced Phase Aberrations for Solid-State Laser Amplifiers}, abstract = {Recent scientific endeavors in the realm of relativistic laser plasma physics benefit from the increase of the on-target intensity (~10^21 W/cm2) generated by a sufficiently powerful laser. With the POLARIS laser system in Jena, Germany, the processes of ion or electron acceleration, laser-based x-ray generation, high intensity laser physics, and laser-based proton radiography can be more adequately understood and improved towards higher particle energies. In order to further fuel the investigation of these interactions, the question remains as to how a state-of-the-art petawatt class laser system can be upgraded. Several paths can be taken to increase the intensity: through improved beam profiles via wavefront aberration corrections, higher energies, and shorter pulse durations. Although diode-pumped solid-state laser systems employing Yb3+-doped active materials, such as POLARIS, can achieve femtosecond pulses with energies in the Joule regime, the focal spot intensity is nevertheless limited by the quality of the laser beam, resulting from strong phase distortions within the beam profile. These phase aberrations are mainly a product of the optical pumping process of the active material, necessary in order to generate population inversion and optical gain. A percentage of the energy from the pump laser is translated into heat through non-radiative transitions, which results in a temperature increase and subsequent refractive index change, based on the dn/dT, photoelastic effect, and expansion of the material. A non-uniform change in the refractive index due to the intensity profile of the pump laser causes the incident wavefront of the seed laser to experience an additional, spatially and temporally varying, phase-shift. This effect, due to the temperature rise in the active material, is referred to as a \dqthermal lens\dq. An additional type of aberration is also formed when a difference exists in the charge distribution of the dopant ions at different energy levels. Since this is based on the amount of population inversion encouraged by the pump, this spatiotemporal phase-shift effect is called a \dqpopulation lens\dq. Both of these aberrations affect the phase profile of the incident seed laser with comparable amplitudes, yet occur on difference time scales. Therefore, revealing the full behavior of the pump-induced phase aberrations in diode-pumped active materials requires a spatially and temporally resolved study. The investigation presented in this thesis accomplishes this through high-resolution interference measurements, gain measurements, and a thermal simulation with COMSOL, verified with a thermal imaging camera. A testbed amplifier was constructed afterwards, which can be used to further observe these aberrations within normal amplifier operation and test relay-imaging vs multi-pass amplification, multiple active materials, and additional accessories utilized within amplifier stages, through multiple diagnostics. The combination of the pump source, active material, and amplifier design topics in this thesis grants a well-rounded insight into the field of diode-pumped solid-state laser systems.}, year = {2016}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=588}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 17422, author = {Polz, J.}, title = {Laser proton acceleration from water micro-droplets and solid hydrogen targets}, abstract = {*}, year = {2016}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://books.google.de/books/about/Laser\_Proton\_Acceleration\_from\_Water\_Mic.html?id=23l3AQAACAAJ}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Thesis { 16907, author = {Kiffer, M.}, title = {Selektive Breitbandanregung von Ionen in einer Penningfalle}, abstract = {This thesis examines the Stored waveform inverse Fourier transform SWIFT-procedure. With this procedure one can excite and remove several ions types selectively from a Penning trap. An excitation with SWIFT is performed by an external electric signal. The first part summaries the foundations of the movement and the excitation in an ideal Penning trap. Afterwards the excitation with SWIFT in a real Penningtrap is analyzed. Here a big discrepancy between the ideal and real trap arise. Therefore a direct selective removal is inefficient. To compensate for this inefficiency the SWIFT-procedure is adapted. The main idea is to use a switch to remove weakly excited ions from the trap. After the excitation the trap voltage is switched to a low value, which reduces the binding energy of the trap. The last part contains the application of the SWIFT-procedure at the ARTEMIS ion trap. During this application ions where selectively removed from the trap. The obtained findings for the SWIFT-procedure will be applied for an application at the HILITE experiment.}, year = {2016}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=582}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 16533, author = {Blumenhagen, K.-H.}, title = {Experimental studies on polarization correlations in hard x-ray Rayleigh scattering}, abstract = {This thesis investigates experimentally the elastic scattering of hard x-rays. Combining the novel technologies of a third-generation synchrotron radiation source and a Si(Li) strip detector which acts as a highly efficient x-ray Compton polarimeter allows to measure the linear polarization of the elastically scattered photons for a highly linearly polarized incident beam. Here, such a polarization transfer is considered for the first time in the hard x-ray regime. With a photon energy of 175 keV and gold as scatterer, a highly relativistic regime is chosen where Rayleigh scattering is the only significant elastic scattering contribution. In addition to the polarization of the elastically scattered photons, also the angular distribution is measured. The data are compared to fully relativistic second-order QED calculations. Both observables are well described by these predictions whereas the form factor approximation fails. The simultaneous measurement of angular distribution and polarization allows to identify spurious agreement of the form factor theory in only one observable. At scattering angles around 90°, the assumption that the incident beam is completely linearly polarized is not sufficient to explain the data. The measured linear polarization of the Compton-scattered photons is used to obtain an independent estimate for the incident beam polarization of about 98{\%} which leads to an agreement between experiment and theory at all measured data points. The significant change introduced by this depolarization of 2{\%} indicates a strong sensitivity on the polarization of the incident beam. In the present experiment, this sensitivity limits the precision, but on the other hand, it allows a precise reconstruction of the incident beam polarization when the theory is established. Here, such a reconstruction is performed and the result agrees with the 98{\%} from the Compton polarization, but with a slightly lower uncertainty and with less statistics.}, year = {2016}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00030049}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17149, author = {S\{\"\{a\}vert, A.}, title = {Few-cycle microscopy of a laser wakefield accelerator}, abstract = {This thesis describes the development and first application of a novel diagnostic for a laser driven wakefield accelerator. It is termed Few‐Cycle Microscopy (FCM) and consists of a high-resolution imaging system and probe pulses with a duration of a few optical cycles synchronized to a high intensity laser pulse. Using FCM has opened a pristine view into the laser‐plasma interaction and has allowed to record high‐resolution images of the plasma wave in real time. Important stages during the wave’s evolution such as its formation, its breaking and finally the acceleration of electrons in the associated wake fields were observed in the experiment as well as in simulations, allowing for the first time a quantitative comparison between analytical and numerical models and experimental results. Using this diagnostic, the expansion of the wave’s first period, the so‐called \grqbubble’, was identified to be crucial for the injection of electrons into the wave. Furthermore, the shadowgrams taken with FCM in combination with interferograms and backscatter spectra have revealed a new acceleration regime when using hydrogen as the target gas. It was found that in this scheme electron pulses are generated with a higher charge, lower divergence and better pointing stability than with helium gas. The underlying pre‐heating process could be attributed to stimulated Raman scattering, which has been thought up till now to be negligible for short (t < 30 fs) laser pulses. However, as it is shown in this thesis, the interplay of the temporal intensity contrast of the laser pulse 1 ps before the peak of the pulse together with a sufficiently high plasma electron density can provide suitable conditions for this instability to grow, resulting in improved electron pulse parameters.}, year = {2016}, month = {6}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00030374}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Phdthesis { 16284, author = {Kurian, F.}, title = {Cryogenic Current Comparators for Precise Ion Beam Current Measurements}, abstract = {The planned Facility for Antiproton and Ion Research (FAIR) at GSI has to cope with a wide range of beam intensities in its high-energy beam transport systems and in the storage rings. To meet the requirements of a non-intercepting intensity measurement down to nA range, it is planned to install a number of Cryogenic Current Comparator (CCC) units at different locations in the FAIR beamlines. In this work, the first CCC system for intensity measurement of heavy ion beams, which was developed at GSI, was re-commissioned and upgraded to be used as a 'GSI - CCC prototype' for extensive optimization and development of an improved CCC for FAIR. After installation of a new SQUID sensor and related electronics, as well as implementation of improved data acquisition components, successful beam current measurements were performed at a SIS18 extraction line. The measured intensity values were compared with those of a Secondary Electron Monitor (SEM). Furthermore, the spill-structure of a slowly extracted beam was measured and analyzed, investigating its improvement due to bunching during the slow-extraction process. Due to the extreme sensitivity of the superconducting sensor, the determined intensity values as well as the adjustment of the system for optimal performance are strongly influenced by the numerous noise sources of the accelerators environment. For this reason, detailed studies of different effects caused by noise have been carried out, which are presented together with proposals to reduce them. Similarly, studies were performed to increase the dynamic range and overcome slew rate limitations, the results of which are illustrated and discussed as well. By combining the various optimizations and characterizations of the GSI CCC prototype with the experiences made during beam operation, criteria for a more efficient CCC System could be worked out, which are presented in this work. The details of this new design are worked out with respect to the corresponding boundary conditions at FAIR. Larger beam tube diameters, higher radiation resistivity and UHV requirements are of particular importance for the cryostat. At the same time these parameters affect the CCC superconducting magnetic shielding, which again has significant influence on the current resolution of the system. In order to investigate the influence of the geometry of the superconducting magnetic shield on different magnetic field components and to optimize the attenuation, FEM simulations have been performed. Based on the results of these calculations, modifications of the shield geometry for optimum damping behavior are proposed and discussed in the thesis.}, year = {2016}, month = {3}, school = {Johann Wolfgang Goethe-Universit\{\"\{a\}t Frankfurt; Fachbereich Physik}, file_url = {http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/40638}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 16056, author = {Klenke, A.}, title = {Performance scaling of laser amplifiers via coherent combination of ultrashort pulses}, abstract = {Laser systems emitting ultrashort pulses have become an indispensable tool in science. However, the performance of a single amplifier is limited by a variety of physical effects. Hence, the coherent combination of ultrashort pulses has been investigated as a way to provide a new power-scaling opportunity. This concept can provide a simultaneous increase of the average power, pulse energy and peak power while preserving the beam quality and temporal pulse profile of a single-amplifier system. Theoretical considerations were carried out to investigate the impact of differences between the pulses on the combination process. It could be shown that their impact is small enough to realize laser systems based on coherent combination experimentally with a good combination efficiency. Additionally, the total combination efficiency converges to a fixed values for an increasing number of channels. The coherent combination concept was demonstrated experimentally with a fiber-CPA system comprising four parallel state-of-the-art amplifiers. In these experiments, the highest peak power emitted from a fiber laser system so far (22GW) could be achieved. Finally, for future systems with a large channel count, the compact integration of these channels will play a major role in reducing the footprint and component count and, therefore, the cost. Experimentally, this was demonstrated by employing a multicore fiber together with a compact beam-splitter design.}, year = {2016}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=571}, note = {papertype:d, rsaps:1, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 16463, author = {Herdrich, M. O.}, title = {Photonen- und Elektronen-Emission von relativistischen Schwerionen beim Durchgang durch Materie}, abstract = {The planned FAIR-complex on the site of the GSI Helmholtz-Center for Heavy-Ion Research establishes a broad bandwidth of new experimental opportunities especially in the area of heavy-ion physics. New efforts to not only use its high-energy storagering HESR for proton-antiproton collisions, but also to open it up for experiments with relativistic heavy ions, are of great importance for the regime of relativistic collisions. They extend the options for atomic-physical studies into so far unreached areas of energy. This allows collision experiments of intensive, well-defined ion beams with virtually the full range of both energy and charge states with a variable gas-target. Electrons and photons released in those interactions lead the way to detailed observations and analysis of atomic structures and processes within the collision system. The planning of future experiments requires preferably pragmatic and precise methods of describing the cross-sections of the most important interaction-processes that lead to the emission of electrons and photons in ion-atom-colissions. In the frame of this work a basic overview of relevant interaction processes of collisions in the new energy range made available beyond 500 MeV/u is summarized. Furthermore the theoretical description of their emission characteristics is collected from already existing work, and used to calculate the energy and angle differential cross-sections and polarisation behaviours for a few processes in a wide range of parameters. The data sets are condensed into a database and compared to the results of other work, to test their quality. In the second part of this work the aquired data is used to plan a possible experiment at the HESR. For one, this demonstrates the practical usability of the database for future experiments. But also, the proposed experiment could be conducted in the initial phase of the storage-ring’s operation. The functionality of the facility could be checked and the effect of negative-polarized x-rays emitted by the radiative electron capture process, which - because of insufficient experimental capabilities - was not detectable yet, could be measured for the first time. Beyond the sole optimization of the experiment’s parameters using the database, several simulations were executed. The efficiency of a possible detector was studied, as well as the detectability of the effect itself under the precalculated experimental conditions. Secondly an analysis of the fraction of the radiation background was performed, that looked at the electrons which are also emitted and their interaction products with the experiment setup. The newly gained insight shows that a measurement of the negative polarization effect at the new storage-ring seems possible, but new problems and challenges arise from the fact that the emitted particles carry much higher energies. For example, binary encounter electrons can reach kinetic energies in the MeV-regime, which may lead to the emission of high energy secondary Bremsstrahlung. This has to be considered when designing the new target-chamber and detectors, and it is crucial for the planning of experiments to come.}, year = {2016}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=584}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 16031, author = {Schulze, K. S.}, title = {Methoden und M\{\"\{o\}\}glichkeiten der hochpr\{\"\{a\}zisen R\{\"\{o\}\}ntgenpolarimetrie}, abstract = {In the visible range, polarimetry is a versatile tool in physics, chemistry and life sciences. Also in the x-ray range, the measurement of polarization changes can be found in a large number of scientific fields. The topic of this work is the analysis of such polarization changes with an extremely high precision. Therefore, two methods of creating very pure linear polarization states are investigated theoretically and experimentally, namely polarimetry with channel-cut crystals and polarimetry based on the Borrmann effect. With these methods, polarization purities reaching ten orders of magnitude can be realized, which enable the precise study of birefringence, dichroism and optical activity. This is demonstrated by different experiments. For instance, a rotation of the polarization plane of less than one arc second was detected during the transmission of an x-ray beam through a sugar solution. Various properties of the polarizers are explained using the dynamical theory of x-ray diffraction. These calculations show that especially at high photon energies the polarization purity is limited by so called umweganregung. Besides the measurement of small polarization changes, the high polarization purity leads also to application in nuclear resonant scattering experiments. Photons that change their polarization during scattering can pass the polarimeter whereas the non-resonantly scattered photons are suppressed by many orders of magnitude. Thus, this method allows a pure measurement of nuclear spectra and lead to the discovery of several quantum optical phenomena in the x-ray range.}, year = {2015}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00027286}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 15862, author = {M\{\"\{u\}\}ller, R. A.}, title = {Radiative recombination in the presence of an intense laser field}, abstract = {In this thesis we present a theoretical study on the radiative recombination of electrons into the ground state of hydrogen like ions in the presence of an intense external laser field. We employ for the description of this process Heisenberg’s S-matrix theory, where the final bound state of the electron is constructed using first order time dependent perturbation theory. Two different initial electron states are considered. First asymptotically plane-wave-like electrons with a separable Coulomb-Volkov continuum wave function and secondly twisted electrons with a well defined orbital angular momentum constructed from Volkov states. Using this approach we perform detailed calculations for the angle-differential and total cross section of laser assisted radiative recombination considering low-Z ions and laser intensities in the range from IL = 10^11 W/cm^2 to IL = 10^13 W/cm^2. Special emphasis is put on the effects arising due to the laser dressing of the residual bound state. It is seen that the bound state dressing remarkably affects the total cross section and manifests moreover as asymmetries in the angular and energy distribution of the emitted photons. For incident Coulomb-Volkov electrons we study moreover the polarization of the emitted recombination radiation. Here we find that the direction of polarization is rotated depending on the energy of the emitted recombination photons.}, year = {2015}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=591}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15418, author = {Jahrsetz, T.}, title = {Two-photon processes in highly charged ions}, abstract = {Two-photon processes are atomic processes in which an atom interacts simultaneously with two photons. Such processes describe a wide range of phenomena, such as two-photon decay and elastic or inelastic scattering of photons. In recent years two-photon processes involving highly charged heavy ions have become an active area of research. Such studies do not only consider the total transition or scattering rates but also their angular and polarization dependence. To support such examinations in this thesis I present a theoretical framework to describe these properties in all two-photon processes with bound initial and final states and involving heavy H-like or He-like ions. I demonstrate how this framework can be used in some detailed studies of different two-photon processes. Specifically a detailed analysis of two-photon decay of H-like and He-like ions in strong external electromagnetic fields shows the importance of considering the effect of such fields for the physics of such systems. Furthermore I studied the elastic Rayleigh as well as inelastic Raman scattering by heavy H-like ions. I found a number of previously unobserved phenomena in the angular and polarization dependence of the scattering cross-sections that do not only allow to study interesting details of the electronic structure of the ion but might also be useful for the measurement of weak physical effects in such systems.}, year = {2015}, month = {3}, school = {Ruprecht-Karls-Universit\{\"\{a\}t; Fakult\{\"\{a\}t f\{\"\{u\}\}r Physik und Astronomie}, file_url = {http://archiv.ub.uni-heidelberg.de/volltextserver/18404/}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Phdthesis { 15450, author = {H\{\"\{o\}\}fer, S.}, title = {Zeitaufgel\{\"\{o\}\}ste R\{\"\{o\}\}ntgenbeugung an einkristallinem Indiumantimonid}, abstract = {In this work the structural changes in the semiconductor indiumantimonide (InSb) after the excitation with an ultrashort laser pulse (60fs) are investigated, by using ultrashort x-ray pulses (100 fs). The source of this ultrashort x-ray pulses is a laser-plasma-x-ray-source. In this source an ultrashort and intense laser pulse is focused to a 20 µm thick metal foil (intensity up to 8*10^16 W/cm^2, wavelength 800 nm), by the produced plasma characteristic x-rays and bremsstrahlung are emitted. To characterize the emitted radiation a novel timepix-detector is used, with this it was possible to detect bremstrahlung up to 700 keV. The typical extinction depth of x-rays is several millimeter and therefore much deeper than the absorption depth of the excitation laser with 100 nm. By using a strong asymmetric Bragg reflection it was possible to adapt the extinction depth from the x-rays to the absorption depth of the optical laser pulse used for excitation. Through this small extinction depth was it possible to measure 2 ps after excitation a strain of 4{\%} in a 4 nm thin layer on the surface. The excitation of the semiconductor is described with different theoretical models, the predicted temporal and spatial evolution of the strain is compared with measured results.}, year = {2014}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00025438}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 15396, author = {Ding, H.}, title = {Study of Radiative Electron Capture in Relativistic Ion-Atom Collisions}, abstract = {Within the frame work of this work, the radiative electron capture (REC) was studied with emphasis on the polarization properties. First, a fast REC calculator was developed, which facilitates the calculation for REC angular differential cross section and degree of linear polarization for initially bare projectiles with kinetic energy between 5 MeV/u and 400 MeV/u. The interpolations of radiative recombination properties performed by this fast calculator are, on the percent level, in agreement with the exact fully relativistic calculations. With the extension of the underlying RR database to 5 GeV/u, this Calculator can be used for the planning and analysis of measurements at the HESR of the future FAIR facility. For example, at the HESR the cross-over of the REC polarization degree to negative values could be studied. Moreover, when taking into account the shielding effects, by using the successive ionization approximation and neglecting the electron-electron correlation, the working domain of the calculator could be, in principle, extended to initially hydrogen- or helium-like projectiles. Second, the data of Xe54+ ions colliding with neutral hydrogen gas at 150.5 MeV/u of energy, measured in 2008 using a 2D position sensitive Si(Li) detector, were analyzed with a sophisticated analyzing routine, which yielded results in good agreement with the currently available theory. The K-REC was found strongly polarized at the observation angle near 90° in the laboratory frame, which leads to the potential of tunable polarized hard X-ray source with energy (up to MeV) and degree of linear polarization tunability. The experimental uncertainty arose mainly from the indefiniteness of the quality factor (polarization sensitivity) of the polarimeter, which was estimated using a series of Monte Carlo simulations each requiring a day or more of computation time. Last but not least, additional experimental work addressing the radiation yield arising from the interaction of high-power lasers with plasmas were performed using plastic scintillators (coupled to PMTs) and a fast multi-channel oscilloscope. It was possible to record the initial radiation burst and also subsequent events due to activation of the experimental setup. The results indicate that the radiation ux in high-power laser environment is much too high to use large-volume, high-stopping power X-ray detectors like the 2D Si(Li) polarimeter.}, year = {2014}, month = {8}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=577}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 15614, author = {Becker, G. A.}, title = {Untersuchung des Einflusses von Targetmaterial, Foliendicken und Intensit\{\"\{a\}tskontrast bei der Optimierung der Laser-Protonen-Beschleunigung}, abstract = {The present thesis reports on the results of a laser-driven ion acceleration experiment carried out at the POLARIS laser located in the Helmholtz-Institute Jena. In this experiment, the laser pulses of POLARIS were focused on thin metal foils. The dominant ion or proton acceleration mechanism in such an experiment is Target Normal Sheath Acceleration (TNSA). As a result of this acceleration process, quasi-thermal proton-spectra are generated with a cut-off energy in the range of MeV. The spectra and therefore the maximum proton energy depend on many experimental parameters. At POLARIS, we investigated the influence of foil thickness, material and the temporal intensity contrast on the maximum achievable proton energy. For this, we used copper, silver, gold, aluminium and tantalum foils with different thicknesses from a few 10’s of micrometers down to 100 nanometer. It was found, that the foil material exerts a strong influence on the maximum proton and an optimal foil thickness was found for most of the materials, where the proton energy attains its maximum. Furthermore the influence of pulse contrast improvement was investigated by using a fast Pockels cell and an alternative front-end based on XPW (cross-polarized wave generation). The contrast improvement resulted in a lower optimal foil thickness, but did not result in a higher maximum proton energy.}, year = {2014}, month = {3}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=583}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15452, author = {Kiefer, T.}, title = {Investigation of the laser-based Target Normal Sheath Acceleration (TNSA) process for high-energy ions \{--\} an analytical and numerical study}, abstract = {The present work is dealing with the theoretical description of laser-driven ion acceleration in the Target Normal Sheath Acceleration (TNSA) process. Various, one-dimensional models describing the laser-heated plasma expansion into vacuum are studied to derive principal relations between the initial conditions of the laser-target interaction \{--\}- such as electron parameters, laser and target properties \{--\}- and the ion spectra and maximum ion energies which can be observed in experiments. In the first part of this work, two different approaches for the description of the hot electron population are compared when applied to these models. It turns out that a hydrodynamic ansatz for the electron density, which has widely been used in the literature, is contained in the general kinetic treatment of the electrons under the assumption of a particular class of electron energy distributions. Especially, this class contains a step-like electron energy. The impact of a step-like hot electron energy distribution on the ion acceleration process is described in the second part of this thesis. The application of the various adiabatic plasma expansion models to the data from ultrashort-pulse experiments convincingly shows that the analytic results of the expansion model assuming a step-like electron energy distribution reproduce the observed maximum ion energies and the corresponding ion spectra quite well, while this is not the case for the models assuming Maxwellian electron distributions. The third part of this work covers the impact of an initial density gradient at the rear surface of the target. The developed model is able to closely reproduce the experimentally observed relation between the maximum ion energy and the initial target thickness. By using the model prepulse effects in the plasma expansion process can be considered, explaining the experimental observation of an optimal target thickness.}, year = {2014}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00024063}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Phdthesis { 15441, author = {R\{\"\{o\}\}del, C.}, title = {Synthese von extrem ultravioletter Strahlung an relativistischen Plasmaoberfl\{\"\{a\}chen}, abstract = {In this thesis, high harmonic radiation is studied which is generated by the relativistic interaction of intense laser pulses with dense plasma surfaces. Laser plasma simulations are performed by the author and by colleagues from the University of Dusseldorf for interpreting the experimental results. At first glance, these simulations predict such a high generation efficiency of harmonics from relativistically oscillating mirrors (ROM) that they have been considered as the next generation attosecond light source for the last 15 years. The objective of this thesis is the spectral characterization of the harmonics' efficiency and the ROM process utilizing calibrated XUV diagnostics. The first step, that has been pursued in the thesis work, is the generation of ROM harmonics at the terawatt laser systems JETI and ARCTURUS operated by the University of Jena and the University of D\{\"\{u\}\}sseldorf, respectively. According to the wide-spread belief, the efficient generation of ROM harmonics requires extremely short plasma density gradients which calls for high intensity laser pulses with excellent temporal contrast. For this reason, a plasma mirror system has been installed at both laser systems to improve the pulse contrast by two or three orders of magnitude depending of the target material. In experiments using contrast-enhanced laser pulses, a stable emission of ROM harmonics was observed. However, the highest yield has been measured for the intermediate pulse contrast which results in a plasma scale length L^ROM\_P=lambda/5. Surprisingly, the overall efficiency of ROM harmonics decreases for shorter scale lengths < lambda/10 or high contrast, respectively. A strong signal of ROM harmonics could even be measured - indeed unstable - without any contrast improvement. Laser plasma simulations confirm the experimental observation of an optimum plasma scale length L^ROM\_P=lambda/5. Two effects have been identified which lead to the reduction of the ROM harmonics' yield for short plasma scale lengths: First, the laser field at the plasma surface is reduced for very short plasma scale lengths. Second, the oscillating electron plasma at the plasma surface is held back by strong electrostatic fields due to the immobile ion background for short plasma density gradients. As a conclusion, the use of an intermediate plasma density gradient for generating ROM harmonics with highest efficiency has to be considered as a paradigm shift in this research field since previous work has called for the highest possible pulse contrast or the shortest plasma scale length, respectively, in order to generate ROM harmonics at all. Using the optimized plasma scale length, a significant modulation and broadening of the ROM harmonic lines has been observed which is unfavorable for most of the potential applications of ROM harmonics. Laser plasma simulations reproduce the fine structure of the harmonic lines. They further reveal an unequally spaced attosecond pulse train and a positive chirp of the harmonics which is associated with the line broadening. This positive chirp is characteristic for ROM harmonics generated at expanded plasma density profiles and is explained by a temporal denting of the plasma surface due to radiation pressure. It is shown by simulations and experiments that the harmonics' linewidth can be minimized when the harmonics' chirp is compensated by chirped driving laser pulses. For optimized preplasma conditions, the efficiency of the ROM harmonics was measured to be 10^-4 at 40nm and 10^-6 at 20nm per harmonic order and falls short of expectations nurtured by 1D PIC-simulations and plasma theory. Having a pulse energy in the order of a µJ per harmonic order, ROM harmonics are indeed suited, e. g., for seeding XUV free-electron lasers or coherent diffraction imaging. However, the efficiency of ROM harmonics of 10^-4 at 40nm is comparable to that of high harmonic generation in gaseous media which is state-of-the-art and technologically much less demanding. Considering the present results of the ROM harmonics' efficiency, the high expectations of a highly-efficient, next-generation attosecond source have not been met yet. The reason for the rather low efficiency of ROM harmonics has been investigated by means of 2D simulations. These simulations reveal surface plasma waves which can be generated in addition to the ROM oscillation and lead to a reduced harmonic emisson in the direction of reflection. Surface plasma waves could thus be responsible for the low efficiency of ROM harmonics measured in the experiments. The simulations suggest that shorter pulses with few-cycle pulse duration should be used in the future for a more efficient generation since surface plasma waves can not be built up at these time scales. A prerequisite for most of the potential applications of ROM harmonics is the generation with a high repetition rate. Using fast-rotating targets and frequency-doubled laser pulses surface harmonics have been generated with the 10-Hz repetition rate of the JETI laser system. Due to the frequency-doubling process the pulse contrast is enhanced by several orders of magnitude such that extremely short plasma density gradients are obtained. Surprisingly, an effect was discovered which was not predicted by theory so far: The high harmonic spectra show a significant enhancement of particular harmonic orders located at twice the maximum plasma frequency 2 omega\_P or 2 omega\_P +- 2 omega\_L. By using targets of different density we were able to tune the enhancement in a certain frequency range in the XUV. Moreover, the efficiency of the amplified harmonics is even higher than the one which is measured for the optimized plasma scale length. Laser plasma simulations confirm then experimental results and reveal the origin of the enhancement: The plasma surface oscillates relativistically with the laser frequency omega\_L and the plasma frequency omega\_P. The enhanced harmonics are due to a ROM-like oscillation at omega\_P. A simple model based on the ROM model can explain the enhanced harmonics as a frequency-mixing process which utilizes the relativistic nonlinearity induced by retardation. This relativistic frequency synthesis at plasma surfaces can be regarded as a new regime of nonlinear optics in the XUV which employs plasma frequencies of dense surface plasmas in the order of several PHz. At the end of the thesis, two selected applications of ROM harmonics are discussed: The generation of intense attosecond pulses by the ROM process would enable XUV-XUV pump-probe experiments providing attosecond time resolution. However, such experiments would require the determination of the attosecond time structure of ROM harmonics first. An apparatus has been constructed which allows the measurement of an attosecond pulse train by using a nonlinear autocorrelation technique. The second potential application of ROM harmonics is a non-invasive cross-sectional imaging technique which has been developed during the thesis work. This method provides a depth resolution of a few nanometers and employs broad-bandwidth XUV or soft x-ray radiation. ROM harmonics with a nearly continuous spectrum could be a suitable radiation source for this application of technical and industrial relevance.}, year = {2014}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=578}, note = {papertype:d, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 15449, author = {Wustelt, P.}, title = {Ionisation atomarer Ionen in intensiven Laserfeldern}, abstract = {In this work a momentum resolved study of strong field multiple ionization is presented. Atoms exposed to super-intense laser pulses can be ionized to high charge states. In the optical regime, the ionization probability depends highly nonlinear on the field strength. Therefore, for a pulsed field, ionization is concentrated in a narrow intensity and a correspondingly narrow time interval for each ionization step. Using a fast ion beam, the multi-electron strong-field ionization dynamics of atomic ions is investigated as function of the laser polarization state and the laser intensity. In the experiment, a beam of Ne+ ions is produced in a hollow-cathode discharge duoplasmatron ion source and accelerated to an energy of 8 keV. Intensities of up to about 10^17 W/cm2 are achieved in the interaction region using 10-mJ laser pulses with a pulse duration of 35-fs pulses. The three-dimensional momentum distributions are reconstructed from the time and position information recorded for each ion by a delay-line detector. In contrast to linear polarization, for elliptically polarized many cycle pulses, the final ion momentum distribution in single ionization provides direct and complete information on the ionizing field strength as well as the ionization time. A deconvolution method was developed, which allows the reconstruction of the electron momenta from the final ion momentum distributions after multiple ionization up to four sequential ionization steps and within a retrieval of the ionization field strength as well as on the release times for subsequent ionization steps. The results are compared to predictions from classical Monte-Carlo simulations based on quasistatic ionization rates. In addition, the subtle effects of the Coulomb interaction on the electron trajectory lead to a tilt in the observed momentum distribution. These effects can be used to study the kinematics and the initial conditions of the electron following tunnel ionization.}, year = {2013}, month = {12}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=595}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15402, author = {Riedel, R.}, title = {Pulse Metrology Tool and Burst-Mode Laser Amplifier for the Free-Electron Laser in Hamburg}, abstract = {The full scientific potential of high repetition rate free-electron lasers is still not exploited. The attainable resolution of time-resolved experiments is limited by fluctuating temporal pulse properties due to the self-amplified spontaneous emission process. To overcome this limitation, the temporal characterization of free-electron laser pulses was improved by the development of a single-shot temporal pulse metrology tool, based on a solid-state cross-correlation technique. The method is based on probing the optical transmission change of a transparent solid material pumped by a free-electron laser pulse. A comprehensive theoretical model allows the reconstruction of the free-electron laser pulse structure. Pulse duration measurements were performed at the Free-Electron Laser in Hamburg, FLASH, yielding 184 fs at 41.5 nm wavelength and sub-40 fs at 5.5 nm. Online measurements during a running experiment are possible with a residual soft-X-ray transmission of 10-45{\%}. A resolution of sub-10 fs can be attained, provided that sufficiently short optical probe pulses are available. Achieving the full performance of high repetition rate free-electron lasers, such as FLASH, requires also optical laser systems with a high repetition rate. A novel burst-mode optical parametric chirped-pulse amplifier is being developed for high-resolution pump-probe experiments and seeding of FLASH at its full repetition rate of 100 kHz-1 MHz. In this work, a first prototype was tested, delivering 1.4 mJ pulse energy and a spectral bandwidth supporting sub-7 fs pulse duration at 27.5 kHz intra-burst repetition rate. A passive pump-to-signal synchronization method was developed for long-term stability with sub-7 fs root mean square jitter between pump and signal pulses. The developed amplifier technology is scalable to high average powers for the future generation of kilowatt-pumped ultrashort laser amplifiers.}, year = {2013}, month = {12}, school = {Universit\{\"\{a\}t Hamburg; Fakult\{\"\{a\}t f\{\"\{u\}\}r Mathematik, Informatik und Naturwissenschaften}, file_url = {https://ediss.sub.uni-hamburg.de/handle/ediss/5213}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 15404, author = {Ecker, B.}, title = {Entwicklung koh\{\"\{a\}renter Lichtquellen im XUV-Regime}, abstract = {Due to their short wavelength and very narrow spectral bandwidth, plasma-basedrnx-ray lasers present an interesting diagnostic tool for a variety of applications, amongst them spectroscopy, microscopy and EUV-lithography. However, up to date x-ray lasers find only limited use in applications, which is related to low pulse energies and an insufficient quality of the x-ray laser beam. Within this context, tremendous efforts have been achieved over the last few years. The simultaneous improvement of pump laser systems as well as pumping mechanisms lead to compact x-ray laser sources operated with up to 100 Hz. To achieve both, higher pulse energies and beam quality, including full spatial coherence, intense theoretical and experimental studies have been performed.rnIn the presented work, a new experimental design has been developed that allowsrnfor pumping two independent x-ray laser targets at the same time. Within the so-rncalled Butterfly configuration, the x-ray laser pulse generated by the first target is used as a seed pulse. It is injected into the second x-ray laser medium, which acts as an amplifier. This results in the circumvention of undesirable effects, which are related to the amplification of spontaneous emission and limit the beam quality of the x-ray laser. For the first time, the Butterfly setup provides an efficient pumping scheme for both the seed- and the amplifier-target, including travelling wave excitation.rnA first experimental campaign has succeeded in demonstrating a seeded and amplified silver x-ray laser at 13.9 nm and 1 µJ pulse energy. In addition, the measured data reveals the 3 ps lifetime of the population inversion within the silver plasma.rnIn a follow-up experiment, a molybdenum x-ray laser at 18.9 nm was characterized.rnIn addition to the regular pumping scheme used at GSI, a novel pumping strategyrnhas been deployed, which relies on an additional pumping pulse. Seeded x-ray laser operation has been demonstrated in both schemes, resulting in x-ray laser pulses of up to 240 nJ. The peak brilliance of the amplified x-ray laser was two orders of magnitude larger compared to the original seed pulses, and more than one order of magnitude larger compared to an x-ray laser based on a single target. The experimental setup developed and deployed in this work holds the promise to provide extremely brilliant plasma-based x-ray lasers with full temporal and spatial coherence.rnThus, the presented experimental concept presents a highly interesting alternative to the currently more common approach relying on high-order harmonic pulses as a seed source.rnThe results obtained and discussed in this work are a valuable contribution in the development of an x-ray laser for spectroscopy experiments on highly-charged heavy-ions. These experiments are scheduled at the experimental storage ring at GSI, as well as the high-energy storage ring of the future FAIR facility}, year = {2013}, month = {11}, school = {Johannes Gutenberg-Universit\{\"\{a\}t Mainz; Fachbereich 08 Physik, Mathematik und Informatik}, file_url = {http://doi.org/10.25358/openscience-1781}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Mastersthesis { 15375, author = {Hahn, C.}, title = {Energie- und polarisationssensitiver Nachweis harter R\{\"\{o\}\}ntgenstrahlung an Hochintensit\{\"\{a\}tslasern}, abstract = {The present thesis details the extensive calibration and characterization of two CdTe-based semiconductor detectors equipped with Timepix-class readout chips, and presents first results of polarimetric measurements conducted with these sensors. The readout's Time-over-Threshold mode provides a means to measure the energy deposited in each of the 65k sensor pixels, opening the way for a compact and versatile Compton polarimeter for the high-energy X-ray regime that is commonly encountered at, e.g., laser-generated plasmas. Since each pixel features its own dedicated set of conversion electronics, an individual calibration of every pixel is mandatory if the full potential of the energy-sensitive detection mode is to be exploited. Exposures to both gamma and X-ray fluorescence radiation were used to generate the necessary data. In addition, a range of MATLAB programs and classes was created to facilitate the lengthy analyses. The final obtainable energy resolution is on the order of 9{\%}, with higher bias voltages providing some potential for improvement while simultaneously increasing the observed detector noise. The fraction of charge-sharing events, i.e. those that encompass multiple pixels, was found to conform with expectations, increasing with the incident photon's energy while, for a given energy, being somewhat lower at higher bias voltages. Furthermore, a two-detector Compton polarimeter was constructed where two Timepix detectors are arranged around a passive scattering target of approximately 1 cm diameter, covering azimuthal scattering angles that differ by 90°. This setup was first tested at DESY's PETRA III accelerator. The observed stark contrast between radiation scattered parallel and perpendicular to the incident photon electric field vector confirms the setups' fitness for Compton polarimetry in the energy range of some 100 keV. By adding a Tantalum plate collimator to further restrict the scattering angle of the incident photons, the contrast between both detectors was enhanced by an additional 18{\%}. In this configuration, the setup almost reached the contrast theoretically expected for an ideal Compton polarimeter.}, year = {2013}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=568}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15444, author = {Geithner, R.}, title = {Optimierung eines kryogenen Stromkomparators f\{\"\{u\}\}r den Einsatz als Strahlmonitor}, abstract = {The non-destructive, non-reactive monitoring of particle beams in the nA range is one of the challenges in the accelerator technology. One way of achieving this objective is the detection of the azimuthal magnetic field created by the particle beam. In the present work a detection system was optimized in terms of noise limited resolution which is based on the principle of the Cryogenic Current Comparator (CCC). In the case of the CCC, the measurement of the magnetic field is realized with a superconducting pick-up coil and a superconductor current sensor (DC-SQUID), which are surrounded by a superconducting shield. It can be shown that the noise-limited resolution of the detector is determined primarily by the low-temperature properties of the pick-up coil and therewith the ferromagnetic core material used in the coil. To this end, extensive temperature and frequency-dependent studies on amorphous and nanocrystalline core materials with respect to their permeability and their noise contribution were carried out. Based on the results obtained an optimized cryogenic current comparator was set up, its noise-limited resolution was significantly reduced compared to previous models already tested.}, year = {2013}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00023556}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 17421, author = {Rathje, T.}, title = {Photodissoziation des Wasserstoffmolek\{\"\{u\}\}lions durch Einzelzyklenlaserpulse}, abstract = {*}, year = {2013}, month = {10}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=598}, note = {papertype:d, rsaps:0, filetype:pdf, hij:0, public:1,} } @Thesis { 15416, author = {Herdrich, M. O.}, title = {Ionisationsquerschnitte von Uranionen in Speicherringen}, abstract = {For many experiments at accelerator facilities high luminosities are necessary, which are only achievable with highest ion beam intensities. Some of the experiments planned for the FAIR project need beam intensities up to a few 10^11 heavy ions in order to observe effects having extremely low reaction cross-sections. Furthermore, applications like the ion-driven fusion require high-intensity beams with beam currents up to 200 Ampere in total. Low charged particles have to be used, because space charge effects limit the maximum expected intensity and phase space volume of the ion beams. However, in typical beam energy regimes above 1 MeV/u, these particles are far from their equilibrium state, resulting in charge changing events during interactions with the residual gas of the accelerator tubes occurring more frequently. In ring accelerators these effects lead to the loss of ions, which for high intensities and high repetition-rates can result in dynamic processes leading to a sudden loss of the whole beam. To minimize the impact of such charge changing effects, a good understanding and characterization of the underlying processes is crucial. The theoretical description of dynamical processes in many electron systems is challenging and can only be done in an approximate way. Therefore an experimental validation of the theoretical predications within a broad parameter range is needed. For this purpose, beam lifetime experiments with two typical uranium charge states, namely U^28+ and U^73+, at three beam energies (30,50 and 150 MeV/u) have been carried out at the ESR storage-ring of the GSI Helmholtz Center for Heavy Ion Research, to determine their ionization cross-section in interactions with several different target gases.}, year = {2013}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=579}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 15432, author = {Seegert, N.}, title = {Quantum Reflection at Strong Magnetic Fields}, abstract = {The zero-point energy of the quantum electrodynamical vacuum manifests itself through the existence of virtual electron-positron fluctuations. Real electromagnetic fields now have the ability to couple to these fluctuations, and the quantum vacuum hence facilitates a variety of nonlinear interactions between electromagnetic fields. The present work aims at introducing and investigating the effect of quantum reflection as a new means of probing the quantum vacuum nonlinearity. The term quantum reflection is commonly employed to describe the reflection of atoms, quantum mechanically regarded as matter waves, from attractive potentials. This effect can be used to investigate the surface of condensed matter by shining probe particles onto it at grazing incident angles. The reflected particles are then a superposition of both atoms reflected classically at the repulsive surface of the condensed matter as well as atoms subjected to quantum reflection due to the attractive long range potential. This work now suggests to carry over this mechanism to the purely optical case by employing a highly sensitive \dqpump-probe\dq setup. A strong magnetic background field, created by a pump laser, modifies the QED vacuum to act as an effective potential for traversing probe photons. Since the magnetic field exhibits a spatial (as well as temporal) inhomogeneity, we expect the incoming probe photons to be partially reflected from the region of the inhomogeneity. In our analogy the probe photons play the role of the atoms, while the magnetized quantum vacuum plays the role of the attractive potential created by the condensed matter surface. However, probe photons unaffected by the vacuum fluctuations simply pass the entire region of inhomogeneity. This is in contrast to quantum reflection in the atomic case, where the repulsive potential of the condensed matter gives rise to a large background. We therefore end up with a highly sensitive setup possessing an inherent signal-background separation, which should prove to be an important advantage compared to other experiments aiming to probe fluctuation-induced nonlinearities of the quantum vacuum. Owing to the smallness of the nonlinear effects, one of the biggest challenges for such standard experiments is usually given by the separation of photons carrying the optical signatures from such photons which were unaffected by the fluctuations. First, we lay down the theoretical foundations to describe quantum reflection, and investigate the effect for time-independent magnetic background fields varying in one spatial dimension. We then analyze various background profiles and give estimates for the number of reflected photons employing the design parameters of typical high-intensity laser facilities. The last part deals with a possible extension of the formalism to time-dependent fields.}, year = {2013}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=586}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Thesis { 15414, author = {M\{\"\{u\}\}ller, R. A.}, title = {Angular and Polarisation Properties of Bremsstrahlung Radiation in the Short-Wavelength Limit}, abstract = {In this work two methods for the description of atomic bremsstrahlung are discussed. The density matrix of the system after the scattering process is derived using a Rayleigh expansion of the photon interaction operator and a partial wave expansion of the free dirac electron. These derivations were done following Yerokhin and Surzhykov as well as Tseng and Pratt. From these results a new parametrisation of two observables of electron-atom bremsstrahlung is presented which expresses the angular distribution and the degree of linear polarisation in terms of spherical harmonics. That means once the coefficients are calculated the calculation of the bremsstrahlung properties is orders of magnitude faster than the calculations after Yerokhin and Surzhykov [6]. Also almost real-time calculations are possible when the tabulated coefficients are used. The coefficients yield a couple of symmetry relations and converge very fast against zero which reduces the needed expansion order remarkably. Also they behave very smooth when the other parameters are changed so we can get the coefficients for arbitrary parameter sets from an interpolation on a two dimensional grid. The number of coefficients needed increases with the photon energy but does not exceed 50 for energies up to several hundred keV while for energies less than 100keV for most applications a monadic number of coefficients is enough. Additionally the distance between the nodes on the grid can be increased for higher energies because the coefficients vary less for higher energies so less sets of coefficients are necessary to achieve the same accuracy.}, year = {2013}, month = {8}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=593}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 15440, author = {Blinne, A.}, title = {Paarproduktion in rotierenden elektrischen Feldern}, abstract = {Schwinger pair production from the vacuum in rotating time-dependent electric fields is studied using the real-time DHW formalism. This formalism is shortly introduced in general and a specific equation of motion for the purpose of this thesis is derived. Using this equation the time evolution of the Wigner function as well as asymptotic particle distributions neglecting back-reactions on the electric field are determined. Whereas qualitative features can be understood in terms of effective Keldysh parameters, the field rotation leaves characteristic imprints in the momentum distribution that can be interpreted in terms of interference and multiphoton effects.}, year = {2013}, month = {3}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=567}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Mastersthesis { 15447, author = {Kienel, M.}, title = {Passive Coherent Beam Combining of Temporally Cascaded Pulses}, abstract = {High-power ultrafast lasers are beneficial for a vast number of applications ranging from fundamental science all the way to industrial scale materials processing. Especially ytterbium-doped fiber lasers have proven to allow for high average power, high pulse energy and remarkable efficiency at the same time. Therefore, they are ideal candidates for most applications. Over the past decades, their output parameters have been scaled by orders of magnitude. However, further power increase is limited by nonlinear and thermal effects, which cause detrimental distortions of the pulses and beams. Promising approaches to overcome these limitations are spatial and temporal coherent beam combination. In this technique, the power and the scaling challenges are distributed among several pulses during the amplification process and afterwards the pulses are combined into a single output pulse. Thereby, the system efficiency is the most crucial parameter, which describes the quality of the pulse combination. Coherent beam combination can be implemented with an (active) or without (passive) a stabilization system. In this work, simultaneous implementing of both spatial and temporal beam combining has been investigated in a passively stabilized setup. A cascaded Sagnac interferometer-type implementation has been used to generate and combine two pulse trains of up to four pulses each. An ytterbium-doped fiber amplifier was placed inside the Sagnac loop and was used as main amplification stage of a pre-existing chirped-pulse-amplification system. Temporal delays of 7 ns and 14 ns for the temporal division of 2 ns stretched pulses have been realized. Investigations at low pulse energy showed system efficiencies larger than 80{\%} that decreased to >60{\%} for high pulse energy. Based on simulations it was shown that this degradation is due to differences of the accumulated nonlinear phases of the divided pulses. An actively stabilized setup is proposed, which is able to compensate for the differences in nonlinearities.}, year = {2013}, month = {1}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=581}, note = {papertype:m, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15419, author = {L\{\"\{o\}\}tzsch, R.}, title = {Bent crystal X-ray optics for the diagnosis and applications of laser-produced plasmas}, abstract = {The present work deals with x-ray optics based on bent crystals. Such crystals are used for monochromatic imaging and high-resolution x-ray spectroscopy of laser-produced plasmas. In this thesis, the reflection properties of perfect, elastically bent crystals are investigated and it is shown, that the elastic deformations of these crystals depends not only on the depth in the crystal, as hitherto considered, but also on the lateral coordinates. Beneath these fundamental investigations, the thesis presents a variety of x-ray optics, which demonstrate their application potential. This includes two optics, which are used in the field high repetition rate x-ray sources based on laser-produced plasmas. Furthermore, a new application of toroidally bent crystals presented. These crystals allow for a scheme to measure crystal rocking curves with both great angular and spatial resolution. With this technique, it is possible to detect lateral variations of strain in the order of 10-5 and with lateral resolution better than 20 µm. The last part of the thesis presents an experiment from the field of x-ray spectroscopy of laser-produced plasmas. X-ray emission of ions in high electric fields is analyzed. Therefor the emission of these ions has to be recorded at laser intensities of 1020 W/cm² with high dynamics. To this end, a new spectrometer is developed, which allows to detect the transient subtle changes in the spectra caused by electric fields in the order of TV/m, which are created in laser-plasma experiments.}, year = {2012}, month = {11}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {https://www.db-thueringen.de/receive/dbt\_mods\_00022009}, note = {papertype:d, rsaps:1, filetype:null, hij:0, public:1,} } @Phdthesis { 15445, author = {Aurand, B.}, title = {Untersuchungen zu Mechanismen der Laser-Teilchenbeschleunigung}, abstract = {Within the last decade, many developments towards higher energies and particle numbers paved the way of particle acceleration performed by high intensity laser systems. Up to now, the process of a field-induced acceleration process (Target-Normal-Sheath-Acceleration (TNSA)) is investigated the most. Acceleration occurs as a consequence of separation of charges on a surface potential. Here, the broad energy spectrum is a problem not yet overcome although many improvements were achieved. Calculations for intensities higher than 10^(20..21) W/cm^2 give hint that Radiation-Pressure-Acceleration (RPA) may lead to a sharper, monoenergetic energy spectrum. Within the framework of this thesis, the investigation of the acceleration mechanism is studied experimentally in the intensity range of 10^19 W/cm^2. Suitable targets were developed and applied for patent. A broad range of parameters was scanned by means of high repetition rates together with an adequate laser system to provide high statistics of several thousands of shots, and the dependence of target material, intensity, laser polarisation and pre plasma-conditions was verified. Comparisons with 2-d numeric simulations lead to a model of the acceleration process which was analyzed by several diagnostic methods, giving clear evidence for a new, not field-induced acceleration process. In addition, a system for a continuous variation of the polarization based on reflective optics was developed in order to overcome the disadvantages of retardation plates, and their practicability of high laser energies can be achieved.}, year = {2012}, month = {6}, school = {Johannes Gutenberg-Universit\{\"\{a\}t Mainz; Fachbereich 08 Physik, Mathematik und Informatik}, file_url = {http://doi.org/10.25358/openscience-2060}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Mastersthesis { 15448, author = {Fuchs, S.}, title = {Optische Koh\{\"\{a\}renztomografie mit kurzen Wellenl\{\"\{a\}ngen}, abstract = {n/a}, year = {2012}, month = {4}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=597}, note = {papertype:t, rsaps:0, filetype:pdf, hij:0, public:1,} } @Thesis { 15369, author = {Hahn, C.}, title = {Charakterisierung ortsaufl\{\"\{o\}\}sender Halbleiterdetektoren f\{\"\{u\}\}r harte R\{\"\{o\}\}ntgenstrahlung}, abstract = {The present thesis details the properties of position-sensitive detectors suited for the Compton polarimetry of high-energy X-ray radiation, investigating double-sided Ge(i) and Si(Li) strip detectors as well as a CdTe-based sensor equipped with the novel Timepix detection chip. In the case of the strip detectors, special concern was dedicated to the so-called charge sharing effect, which denotes an incident photon's charge cloud being distributed across several segments. This obviously hampers the determination of the actual interaction position, a crucial parameter for the Compton-polarimetric analysis. A set of sophisticated software routines to recover such events was developed. Using this modified analysis, the number of multiplicity-1 events reported by the Si(Li) detector was increased by about 30{\%}, while the Ge(i) system, having a much smaller strip width, saw an increase by up to a factor of 30 at energies above 200 keV. Consequently, the number of events usable for the Compton analysis, which has to be restricted to exposures with exactly two discernible interactions, grew in a similar fashion, such that, for the Ge(i) sensor, the computed degree of polarization deviated by as much as 9{\%} from previously obtained values. The wide-stripped Si(Li) detector, on the other hand, proved to be much less susceptible to distortions induced through charge splitting. In addition, Timepix acquisitions made during an electron acceleration experiment conducted at the JETI laser system were evaluated. To avoid saturation of the sensor, extensive shielding and indirect exposure, utilizing a plastic body for scattering, were necessary. While the employed Time-over-Threshold mode returns a pixelwise measure for the energy deposition, neither an absolute nor inter-pixel calibration was possible. However, a clear correlation between the total output signal and the intensity reported by an electron spectrometer could be observed, confirming the Timepix sensor's general capability of energy-resolved measurements. Furthermore, electron tracks that were visible in the obtained data were used to calculate a rough estimate of the primary photon energy by comparing their extent to the predictions of the Continuous Slowing Down Approximation. This yielded initial electron energies in the MeV range, which are in good agreement with the achieved energies reported for the JETI experiment in question.}, year = {2011}, month = {9}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=572}, note = {papertype:b, rsaps:0, filetype:pdf, hij:0, public:1,} } @Phdthesis { 15446, author = {M\{\"\{a\}rtin, R.}, title = {R\{\"\{o\}\}ntgenpolarimetrie angewandt zur Untersuchung der Bremsstrahlung spinpolarisierter Elektronen}, abstract = {The present thesis reports on the study of the linear polarization properties of bremsstrahlung produced in polarized electron atom collisions. The experimental investigation of bremsstrahlung photons has been performed using the polarized electron source (SPIN) at the TU Darmstadt. Gold and carbon targets were bombarded with 100 keV electrons whose spin was oriented parallel, anti-parallel and transverse with respect of the beam axis. In addition, an unpolarized electron beam was used for a reference measurement. For the detection of the bremsstrahlung photons, a novel Si(Li) Compton polarimeter has been employed at two different observation angles. This detector enabled the determination of the degree of linear polarization as well as the orientation of the polarization vector for various energies of the bremsstrahlung photons. The emphasis of the work was on the so-called polarization transfer where the polarization of the incoming electron spin influences the polarization of the emitted x-rays. This gives rise to an enhanced degree of linear polarization and to a rotation of the photon polarization vector with respect to the unpolarized case. Both effects were observed by comparing data for the unpolarized and the transversely polarized electron beam. The experimental results are in qualitative agreement with fully relativistic calculations.}, year = {2011}, month = {9}, school = {Ruprecht-Karls-Universit\{\"\{a\}t; Fakult\{\"\{a\}t f\{\"\{u\}\}r Physik und Astronomie}, file_url = {http://archiv.ub.uni-heidelberg.de/volltextserver/12675/}, note = {papertype:d, rsaps:0, filetype:null, hij:0, public:1,} } @Phdthesis { 15613, author = {Reuter, M.}, title = {Interferometric Probing of Laser Generated Plasmas for Electron Acceleration}, year = {2011}, month = {7}, school = {Friedrich-Schiller-Universit\{\"\{a\}t Jena; Physikalisch-Astronomische Fakult\{\"\{a\}t}, file_url = {t3://file?uid=585}, note = {papertype:t, rsaps:0, filetype:pdf, hij:0, public:1,} }