Strong-field frustrated double ionization of argon atoms - Chen, S.; Chen, J.; Paulus, G.; Kang, H. (Physical Review A, 2020)
Using a three-dimensional semiclassical method, we theoretically investigate frustrated double ionization (FDI) of Ar atoms subjected to strong laser fields. The double-hump photoelectron momentum distribution generated from FDI observed in a recent experiment [S. Larimian, Phys. Rev. Research 2, 013021 (2020)2643-156410.1103/PhysRevResearch.2.013021] is reproduced by our simulation. We confirm that the observed spectrum is due to recollision. The laser intensity dependence of FDI is investigated. We reveal that the doubly excited states of Ar atoms and excited states of Ar+ are the dominant pathways for producing FDI at relatively low and high intensities, respectively. The information of which pathway leads to FDI is encoded in the electron momentum distributions. Our work demonstrates that FDI is a general strong-field physical process accompanied with nonsequential double ionization and it can be well understood within the context of recollision scenario.
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Approximating higher-order nonlinear QED processes with first-order building blocks - Dinu, V.; Torgrimsson, G. (Physical Review D, 2020)
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CPC's 50th Anniversary: Celebrating 50 years of open-source software in computational physics - Scott, N.; Hibbert, A.; Ballantyne, J.; Fritzsche, S.; Hazel, A.; Landau, D.; Walker, D.; Was, Z. (Computer Physics Communications, 2020)
To celebrate the leading role Computer Physics Communications (CPC) has played in publishing open-source software in computational physics for over 50 years the editors are delighted to announce this Virtual Special Issue. Since 2018, coinciding with the 50th anniversary of the start of the CPC venture, thirty-two invited articles have been published. Each has been peer reviewed and each bears the header 50th anniversary article’. The special issue is in keeping with CPC's ethos: it is focused on computational physics software and is accompanied by twenty-five software systems. The introduction to the collection also includes a personal reflection on Phil Burke, CPC's founder, by Alan Hibbert, a lifelong colleague, who joined Queen's University with Phil in the autumn of 1967. The distinctive feature of CPC is its Program Library which houses and distributes over 3500 open-source programs in computational physics. The introduction concludes with a description of key events in the history of the Program Library, its association with Queen's University Belfast and its transfer to Elsevier's Mendeley Data repository.
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Dissociation and ionization of HeH+in sub-cycle-controlled intense two-color fields - Oppermann, F.; Wustelt, P.; Florin, T.; Mhatre, S.; Gr{\"{a}fe, S. and Paulus, G. and Lein, M. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2020)
Using quantum-mechanical, one-dimensional, non-Born-Oppenheimer simulations we study the control over the strong-field dynamics of the helium hydride molecular ion HeH+ due to interaction driven by short and strong two-color laser pulses. We calculate yields of two competing fragmentation channels: electron removal and dissociation. We find that by changing the relative phase of the two colors, we can select the dominating channel. Nuclear motion is decisive for explaining ionization in this target. Ionization yields are vastly underestimated when nuclear motion is excluded and they are substantially reduced in the heavier isotopologue HeD+. Coupling of the two lowest electronic states is crucial even for the ground-state dissociation process.
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Front edge velocity of ultra-intense circularly polarized laser pulses in a relativistically transparent plasma - Liu, B.; Meyer-ter-Vehn, J.; Ruhl, H.; Zepf, M. (Plasma Physics and Controlled Fusion, 2020)
The propagation of ultra-intense circularly polarized laser pulses in a relativistically transparent plasma is investigated with the help of particle-in-cell (PIC) simulations. When the incident laser pulse is strong enough to expel almost all electrons from the focal volume, the propagation of the laser front edge is found to be dominated by the balance between the laser radiation pressure and the laser-driven electrostatic pressure. Based on a one-dimensional (1D) model, the laser front edge velocity is predicted to depend on , where n0 is the initial plasma density, nc the critical density and a0 the laser amplitude. PIC simulations show that the theoretical prediction works well for not only 1D but also 2D and 3D geometries.
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Holographic detection of parity in atomic and molecular orbitals - Kang, H.; Maxwell, A.; Trabert, D.; Lai, X.; Eckart, S.; Kunitski, M.; Schoeffler, M.; Jahnke, T.; Bian, X.; Doerner, R.; Faria, C. (Physical Review A, 2020)
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The electron affinity of astatine - Leimbach, D.; Karls, J.; Guo, Y.; Ahmed, R.; Ballof, J.; Bengtsson, L.; Boix Pamies, F.; Borschevsky, A.; Chrysalidis, K.; Eliav, E.; Fedorov, D.; Fedosseev, V.; et al. (Nature Communications, 2020)
One of the most important properties influencing the chemical behavior of an element is the electron affinity (EA). Among the remaining elements with unknown EA is astatine, where one of its isotopes, 211At, is remarkably well suited for targeted radionuclide therapy of cancer. With the At− anion being involved in many aspects of current astatine labeling protocols, the knowledge of the electron affinity of this element is of prime importance. Here we report the measured value of the EA of astatine to be 2.41578(7) hinspaceeV. This result is compared to state-of-the-art relativistic quantum mechanical calculations that incorporate both the Breit and the quantum electrodynamics (QED) corrections and the electron{–}electron correlation effects on the highest level that can be currently achieved for many-electron systems. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements.
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Electron-impact recombination and excitation rates for charge-state-selected highly charged Si ions - Lindroth, E.; Orban, I.; Trotsenko, S.; Schuch, R. (Physical Review A, 2020)
Charge-state selective recombination rate coefficients were measured by time of flight (TOF) analyzed highly charged Si ions extracted from an electron-beam ion trap. Additionally, the combination of simultaneous TOF and x-ray measurements and a separation of the dielectronic recombination contribution in the x-ray spectra is used for extracting electron-impact excitation rate coefficients for several overlaying charge states. Experimentally derived dielectronic recombination spectra for XIII and XIV Si are compared and found in excellent agreement with the results of relativistic many-body perturbation theory calculations.
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Enhancing quantum vacuum signatures with tailored laser beams - Karbstein, F.; Mosman, E. A. (Physical Review D, 2020)
We demonstrate that tailored laser beams provide a powerful means to make quantum vacuum signatures in strong electromagnetic fields accessible in experiment. Typical scenarios aiming at the detection of quantum vacuum nonlinearities at the high-intensity frontier envision the collision of focused laser pulses. The effective interaction of the driving fields mediated by vacuum fluctuations gives rise to signal photons encoding the signature of quantum vacuum nonlinearity. Isolating a small number of signal photons from the large background of the driving laser photons poses a major experimental challenge. The main idea of the present work is to modify the far-field properties of a driving laser beam to exhibit a fieldfree hole in its center, thereby allowing for an essentially backgroundfree measurement of the signal scattered in the forward direction. Our explicit construction makes use of a peculiar far-field/focus duality.
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High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength Problem - Kuhn, S.; Shah, C.; L{\'{o}}pez-Urrutia, J.; Fujii, K.; Steinbr{\"{u}}gge, R.; Stierhof, J.; Togawa, M.; Harman, Z.; Oreshkina, N.; Cheung, C.; Kozlov, M.; Porsev, S.; et al. (Physical Review Letters, 2020)
For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic 2p-3d transitions, 3C and 3D, in Fe XVII ions found oscillator strength ratios f(3C)/f(3D) disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of f(3C)/f(3D)=3.09(8)(6) supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.
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Reliability of ptychography on periodic structures - Tuitje, F.; Eschen, W.; Tadesse, G.; Limpert, J.; Rothhardt, J.; Spielmann, C. (OSA Continuum, 2020)
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Ultra-high precision x-ray polarimetry with artificial diamond channel cuts at the beam divergence limit - Bernhardt, H.; Schmitt, A.; Grabiger, B.; Marx-Glowna, B.; Loetzsch, R.; Wille, H.-C.; Bessas, D.; Chumakov, A.; R{\"{u}}ffer, R.; R{\"{o}}hlsberger, R.; St{\"{o}}hlker, T.; Uschmann, I.; et al. (Physical Review Research, 2020)
We report on the use of synthetic single-crystal diamonds for high definition x-ray polarimetry. The diamonds are precision mounted to form artificial channel-cut crystals (ACCs). Each ACC supports four consecutive reflections with a scattering angle 2ΘB of 90°. We achieved a polarization purity of 3.0×10−10 at beamline ID18 of the European Synchrotron Radiation Facility (ESRF). When the x-ray beam's horizontal divergence was reduced through additional collimation from 17 to 8.4μrad, the polarization purity improved to 1.4×10−10. Precision x-ray polarimetry thus has reached the limit, where the purity is determined by the divergence of the beam. In particular, this result is important for polarimetry at fourth generation x-ray sources, which provide diffraction-limited x-ray beams. The sensitivity expected as a consequence of the present work will pave the way for exploring new physics such as the investigation of vacuum birefringence.
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A Synchronized VUV Beamline for Time Domain Two-Color Dynamic Studies at FLASH2 - Appi, E.; Papadopoulou, C.; Mapa, J.; Wesavkar, N.; Jusko, C.; Mosel, P.; Ali{{s}}auskas, S.; Lang, T.; Heyl, C.; Manschwetus, B.; Braune, M.; Brachmanski, M.; et al. (Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2020)
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Compact, Alignment-Free, Environmentally Stable Dispersion Compensated Femtosecond Yb-Fiber Oscillator - Ma, Y.; Salman, S.; Li, C.; Mahnke, C.; Fellinger, J.; Mayer, A.; Heckl, O.; Heyl, C.; Hartl, I. (Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2020)
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Electron trajectories associated with laser-driven coherent synchrotron emission at the front surface of overdense plasmas - Cousens, S.; Yeung, M.; Zepf, M.; Dromey, B. (Physical Review E, 2020)
We present an in-depth analysis of an ultrafast electron trajectory type that produces attosecond electromagnetic pulses in both the reflected and forward directions during normal incidence, relativistic laser-plasma interactions. Our particle-in-cell simulation results show that for a target which is opaque to the frequency of the driving laser pulse the emission trajectory is synchrotronlike but differs significantly from the previously identified figure-eight type which produces bright attosecond bursts exclusively in the reflected direction. The origin and characteristics of this trajectory type are explained in terms of the driving electromagnetic fields, the opacity of the plasma, and the conservation of canonical momentum.
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Factor 40 Pulse Post-Compression of 200 W in-Burst Average Power Pulses via Single-Stage Multi-Pass Spectral Broadening - Balla, P.; Wahid, A.; Sytcevich, I.; Guo, C.; Sch{\"{o}}nberg, A.; Viotti, A.-L.; Silletti, l.; Cartella, A.; Ali{{s}}auskas, S.; Tavakol, H.; Grosse-Wortmann, U.; Seidel, M.; et al. (Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2020)
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Pulse Compression to 3-Cycle Duration beyond 300 W Average Power - Nagy, T.; H{\"{a}drich, S. and Simon, P. and Blumenstein, A. and Walther, N. and Klas, R. and Buldt, J. and Stark, H. and Breitkopf, S. and J{\'{o}}j{\'{a}}rt, P. and Seres, I. and V{\'{a}}rallyay, Z. and Eidam, T. and Limpert, J. (Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2020)
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Relativistic plasma physics in supercritical fields - Zhang, P.; Bulanov, S. S.; Seipt, D.; Arefiev, A. V.; Thomas, A. G. R. (Physics of Plasmas, 2020)
Since the invention of chirped pulse amplification, which was recognized by a Nobel prize in physics in 2018, there has been a continuing increase in available laser intensity. Combined with advances in our understanding of the kinetics of relativistic plasma, studies of laser-plasma interactions are entering a new regime where the physics of relativistic plasmas is strongly affected by strong-field quantum electrodynamics (QED) processes, including hard photon emission and electron-positron (e^+-e^−) pair production. This coupling of quantum emission processes and relativistic collective particle dynamics can result in dramatically new plasma physics phenomena, such as the generation of dense e^+-e^− pair plasma from near vacuum, complete laser energy absorption by QED processes or the stopping of an ultrarelativistic electron beam, which could penetrate a cm of lead, by a hair's breadth of laser light. In addition to being of fundamental interest, it is crucial to study this new regime to understand the next generation of ultra-high intensity laser-matter experiments and their resulting applications, such as high energy ion, electron, positron, and photon sources for fundamental physics studies, medical radiotherapy, and next generation radiography for homeland security and industry.
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Uniform warm dense matter formed by direct laser heating in the presence of external magnetic fields - Wu, D.; Yu, W.; Sheng, Z.; Fritzsche, S.; He, X. (Physical Review E, 2020)
With the recent realization of kilotesla quasistatic magnetic fields, the interaction of a laser with magnetized solids enters an unexplored new regime. In particular, a circularly polarized (CP) laser pulse may propagate in a highly magnetized plasma of any high density without encountering cutoff reflection in the whistler mode. With this, we propose a scheme for producing uniform warm dense matter (WDM) by direct laser heating with a CP laser irradiating onto the target along the magnetic field. It is shown by particle-in-cell simulations, which include advanced ionization dynamics and collision dynamics, moderately intense right-hand CP laser light at 1015W/cm2 can propagate in solid aluminum and heat it efficiently to the 100 eV level within picoseconds. By using two laser pulses irradiating from two sides of a thin solid target, uniform heating to WDM can be achieved. This provides a controllable way to create WDM at different temperatures.
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Versatile Figure-9 Design: How to Access Low-Noise Regimes in an All-PM Yb:Fiber Laser - Mayer, A.; Fellinger, J.; Grosinger, W.; Winkler, G.; Perner, L.; Heyl, C.; Hartl, I.; Heckl, O. (Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2020)
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A compact, turnkey, narrow-bandwidth, tunable, and high-photon-flux extreme ultraviolet source - Hilbert, V.; Tschernajew, M.; Klas, R.; Limpert, J.; Rothhardt, J. (AIP Advances, 2020)
We report on a compact high-photon-flux extreme ultraviolet (XUV) source based on high harmonic generation. A high XUV-photon flux (>10¹³ photons/s) is achieved at 21.8 eV and 26.6 eV. The narrow spectral bandwidth (ΔE/E < 10⁻³) of the generated harmonics is in the range of state-of-the-art synchrotron beamlines and enables high resolution spectroscopy experiments. The robust design based on a fiber– laser system enables turnkey-controlled and even remotely controlled operation outside specialized laser laboratories, which opens the way for a variety of applications.
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A synchronized VUV light source based on high-order harmonic generation at FLASH - Appi, E.; Papadopoulou, C. C.; Mapa, J. L.; Wesavkar, N.; Jusko, C.; Mosel, P.; Ali{{s}}auskas, S.; Lang, T.; Heyl, C. M.; Manschwetus, B.; Brachmanski, M.; Braune, M.; et al. (Scientific Reports, 2020)
Ultrafast measurements in the extreme ultraviolet (XUV) spectral region targeting femtosecond timescales rely until today on two complementary XUV laser sources: free electron lasers (FELs) and high-harmonic generation (HHG) based sources. The combination of these two source types was until recently not realized. The complementary properties of both sources including broad bandwidth, high pulse energy, narrowband tunability and femtosecond timing, open new opportunities for two-color pump-probe studies. Here we show first results from the commissioning of a high-harmonic beamline that is fully synchronized with the free-electron laser FLASH, installed at beamline FL26 with permanent end-station including a reaction microscope (REMI). An optical parametric amplifier synchronized with the FEL burst mode drives the HHG process. First commissioning tests including electron momentum measurements using REMI, demonstrate long-term stability of the HHG source over more than 14 hours. This realization of the combination of these light sources will open new opportunities for time-resolved studies targeting different science cases including core-level ionization dynamics or the electron dynamics during the transformation of a molecule within a chemical reaction probed on femtosecond timescales in the ultraviolet to soft X-ray spectral region.
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Characterization of opening angle correlations of a biphoton state decomposed in Bessel modes - Baghdasaryan, B.; Steinlechner, F.; Fritzsche, S. (Physical Review A, 2020)
The spontaneous parametric down-conversion of photons has been widely applied for generating entangled photon pairs. We theoretically explore the entangled down-converted state of the photon pair, also known as biphoton state, for both degenerate and nondegenerate photon pairs. In particular, the spatial structure of the biphoton state has been expressed in Bessel modes to better understand the correlation with regard to the opening angle Ï'k of Bessel modes. In fact, the opening angles of the down-converted photon pair are not independent of each other, but rather are correlated. Furthermore, we confirm the experimentally observed conditions concerning the optimization of generating high-degree spatial entanglement by controlling the beam waist of the pump beam. We also introduce a new experimental setup for efficient measurement of the spatial entanglement of the biphoton state using geometrical optics arguments.
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High-energy-density-science capabilities at the Facility for Antiproton and Ion Research - Schoenberg, K.; Bagnoud, V.; Blazevic, A.; Fortov, V. E.; Gericke, D. O.; Golubev, A.; Hoffmann, D. H. H.; Kraus, D.; Lomonosov, I. V.; Mintsev, V.; Neff, S.; Neumayer, P.; et al. (Physics of Plasmas, 2020)
The Facility for Antiproton and Ion Research (FAIR) will employ the World's highest intensity relativistic beams of heavy nuclei to uniquely create and investigate macroscopic (millimeter-sized) quantities of highly energetic and dense states of matter. Four principal themes of research have been identified: properties of materials driven to extreme conditions of pressure and temperature, shocked matter and material equation of state, basic properties of strongly coupled plasma and warm dense matter, and nuclear photonics with a focus on the excitation of nuclear processes in plasmas, laser-driven particle acceleration, and neutron production. The research program, principally driven by an international collaboration of scientists, called the HED@FAIR collaboration, will evolve over the next decade as the FAIR project completes and experimental capabilities develop. The first programmatic research element, called “FAIR Phase 0, officially began in 2018 to test components, detectors, and experimental techniques. Phase-0 research employs the existing and enhanced infrastructure of the GSI Helmholtzzentrum f{\"{u}}r Schwerionenforschung (GSI) heavy-ion synchrotron coupled with the PHELIX high-energy, high-intensity laser. The “FAIR Day one” experimental program, presently scheduled to begin in 2025, commences the use of FAIR's heavy-ion synchrotron, coupled to new experimental and diagnostic infrastructure, to realize the envisaged high-energy-density-science research program.
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K-line X-ray fluorescence from highly charged iron ions under dense astrophysical plasma conditions - Deprince, J.; Bautista, M.; Fritzsche, S.; Garc{\'{i}}a, J.; Kallman, T.; Mendoza, C.; Palmeri, P.; Quinet, P. (X-Ray Spectrometry, 2020)
In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K-vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K-line X-ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 10⁵ to 10⁷ K and an electron density ranging from 10¹⁸ to 10²² cm⁻³. In order to do this, relativistic multiconfiguration Dirac-Fock atomic structure calculations have been carried out by considering a time averaged Debye-H{\"{u}}ckel potential for both the electron–nucleus and electron–electron interactions.
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Opportunities for negative ions studies at the Frankfurt Low-energy Storage Ring (FLSR) - Forstner, O.; M{\"{u}}ller, J.; Stiebing, K. (Hyperfine Interactions, 2020)
The room-temperature electrostatic heavy ion storage ring FLSR was originally designed to study the collision dynamics of atoms and molecules. Recently it has been equipped with a RF plasma ion source combined with a charge exchange cell to be able to perform studies with negative ions in the ring. In preliminary experiments beams of He−, O− and OH− could successfully be stored. The measured lifetime of the metastable He−{–}ion is in good agreement with previous results, showing that the lifetime measurement in this case is not limited by the storage time due to collisional detachment. In the case of O− and OH− storage times in the order of seconds have been achieved. In a next step laser beams will be introduced in the ring allowing photodetachment studies of vibrationally cold molecules.
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Strong configuration interaction in the 3p photoelectron spectrum of Kr - Kosugi, S.; Koike, F.; Nagayasu, T.; Hosseini, F.; Martins, J.; Marchenko, T.; Travnikova, O.; Oura, M.; Gejo, T.; Harries, J.; Bozek, J.; Ito, K.; et al. (Physical Review A, 2020)
We measured the Kr photoelectron spectrum in the region close to the 3p ionization threshold. Our high-resolution measurements allowed a clear observation of spectral structures due to electron correlation effects. Analysis based on relativistic multiconfiguration calculations could explain these observed peaks as due to strong configuration interactions between the 3p-1 state and 3d-2nl states. Calculated and experimental data for peak assignments and intensity distributions are in good agreement. In addition, we measured the anisotropy parameter β, which also agreed well with theory. These findings provide a detailed view of strong configuration interactions between the 3p-1 and 3d-2nl inner-shell hole states.
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The photon-ion merged-beams experiment PIPE at PETRA III{–}The first five years - Schippers, S.; Buhr, T.; Borovik Jr., A.; Holste, K.; Perry-Sassmannshausen, A.; Mertens, K.; Reinwardt, S.; Martins, M.; Klumpp, S.; Schubert, K.; Bari, S.; Beerwerth, R.; et al. (X-Ray Spectrometry, 2020)
The Photon-Ion Spectrometer at PETRA III{–}in short, PIPE{–}is a permanently installed user facility at the 'Variable Polarization XUV Beamline' P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. The careful design of the PIPE ion-optics in combination with the record-high photon flux at P04 has lead to a breakthrough in experimental studies of photon interactions with ionized small quantum systems. This short review provides an overview over the published scientific results from photon-ion merged-beams experiments at PIPE that were obtained since the start of P04 operations in 2013. The topics covered comprise photoionization of ions of astrophysical relevance, quantitative studies of multi-electron processes upon inner-shell photoexcitation and photoionization of negative and positive atomic ions, precision spectroscopy of photoionization resonances, photoionization and photofragmentation of molecular ions, and of endohedral fullerene ions.
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A scintillator‐based particle detector for CRYRING@ESR - Hahn, C.; Menz, E.; Pf{\"{a}fflein, P. and Weber, G. and St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
With the unprecedented range of ion species and energies offered by the newly commissioned CRYRING facility, the availability of single ion detectors is of significant importance as part of standard instrumentation as well as for novel experiments. A detector system was constructed on the basis of the YAP:Ce crystal scintillator, which is at once radiation‐hard, fast, and affordable. Results of a characterization experiment confirmed the feasibility of the setup for incident ion rates on the order of MHz and found a critical fluence of some 10¹³ cm⁻² upon which the crystal is rendered locally blind to further ion irradiation. The device was first used in CRYRING commissioning runs in August and November 2018. Future efforts will complete the integration of the detector into the GSI control and data acquisition system MBS.
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Accurate retrieval of ionization times by means of the phase-of-the-phase spectroscopy, and its limits - W{\"{u}}rzler, D.; Skruszewicz, S.; Sayler, A. M.; Zille, D.; M{\"{o}}ller, M.; Wustelt, P.; Zhang, Y.; Tiggesb{\"{a}umker, J. and Paulus, G.G. (Physical Review A, 2020)
By applying recently introduced, phase-of-the-phase spectroscopy [S. Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015)], we analyze the phase-dependent photoelectron signal from Xe ionized in intense, parallel, two-color (1800 nm and 900 nm) laser fields. With such a field configuration, tuning of the relative phase between the ionizing, ω , and the perturbative, 2ω, field results in a modulation of the ionization rate, as well as modifications of the trajectories of electrons propagating in the laser-dressed continuum. Based on a semiclassical model, we confirm that phase dependencies, due to the perturbation of the ionization rate, encode the ionization times of the electrons. Here, using the fork structure, a well-known feature originating from well-defined dynamics allows us to distinguish between electrons ionized within distinct time windows. However, due to the simultaneous perturbation of the electron trajectories, the assignment of the ionization times can be distorted by up to 80 as, i.e., a 10° phase shift, which is independent of the degree of the perturbation.
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Carrier-envelope-phase measurement of few-cycle mid-infrared laser pulses using high harmonic generation in ZnO - Hollinger, R.; Hoff, D.; Wustelt, P.; Skruszewicz, S.; Zhang, Y.; Kang, H.; W{\"{u}}rzler, D.; Jungnickel, T.; Dumergue, M.; Nayak, A.; Flender, R.; Haizer, L.; et al. (Optics Express, 2020)
High-harmonic generation (HHG) in crystals offers a simple, affordable and easily accessible route to carrier-envelope phase (CEP) measurements, which scales favorably towards longer wavelengths. We present measurements of HHG in ZnO using few-cycle pulses at 3.1 µm. Thanks to the broad bandwidth of the driving laser pulses, spectral overlap between adjacent harmonic orders is achieved. The resulting spectral interference pattern provides access to the relative harmonic phase, and hence, the CEP.
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Characteristics of ion beams generated inthe interaction of ultra-short laser pulseswith ultra-thin foils - McIlvenny, A.; Ahmed, H.; Scullion, C.; Doria, D.; Romagnani, L.; Martin, P.; Naughton, K.; Sgattoni, A.; Symes, D. R.; Macchi, A.; McKenna, P.; Zepf, M.; et al. (Plasma Physics and Controlled Fusion, 2020)
Experiments investigating ion acceleration from laser-irradiated ultra-thin foils on the GEMINI laser facility at the Rutherford appleton laboratory indicate a transition to 'light sail' radiation pressure acceleration when using circularly polarised, high contrast laser pulses. This paper complements previously published results with additional data and modelling which provide information on the multispecies dynamics taking place during the acceleration, and provides an indication on expected scaling of these processes at higher laser intensities.
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Detectable Optical Signatures of QED Vacuum Nonlinearities Using High-Intensity Laser Fields - Klar, L. (Particles, 2020)
Up to date, quantum electrodynamics (QED) is the most precisely tested quantum field theory. Nevertheless, particularly in the high-intensity regime it predicts various phenomena that so far have not directly been accessible in all-optical experiments, such as photon-photon scattering phenomena induced by quantum vacuum fluctuations. Here, we focus on all-optical signatures of quantum vacuum effects accessible in the high-intensity regime of electromagnetic fields. We present an experimental setup giving rise to signal photons distinguishable from the background. This configuration is based on two optical pulsed petawatt lasers: one generates a narrow but high-intensity scattering center to be probed by the other one. We calculate the differential number of signal photons attainable with this field configuration analytically and compare it with the background of the driving laser beams.
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Generation of coherent broadband high photon flux continua in the XUV with a sub-two-cycle fiber laser - Klas, R.; Eschen, W.; Kirsche, A.; Rothhardt, J.; Limpert, J. (Optics Express, 2020)
High harmonic sources can provide ultrashort pulses of coherent radiation in the XUV and X-ray spectral region. In this paper we utilize a sub-two-cycle femtosecond fiber laser to efficiently generate a broadband continuum of high-order harmonics between 70 eV and 120 eV. The average power delivered by this source ranges from > 0.2 µW/eV at 80 eV to >0.03 µW/eV at 120 eV. At 92 eV (13.5 nm wavelength), we measured a coherent record-high average power of 0.1 µW/eV, which corresponds to 7 · 109 ph/s/eV, with a long-term stability of 0.8% rms deviation over a 20 min time period. The presented approach is average power scalable and promises up to 1011 ph/s/eV in the near future. With additional carrier-envelop phase control even isolated attosecond pulses can be expected from such sources. The combination of high flux, high photon energy and ultrashort (sub-) fs duration will enable photon-hungry time-resolved and multidimensional studies.
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Giant Isolated Attosecond Pulses from Two-Color Laser-Plasma Interactions - Zhang, Y. X.; Rykovanov, S.; Shi, M.; Zhong, C. L.; He, X. T.; Qiao, B.; Zepf, M. (Physical Review Letters, 2020)
A new regime in the interaction of a two-color (ω,2ω) laser with a nanometer-scale foil is identified, resulting in the emission of extremely intense, isolated attosecond pulses{–}even in the case of multicycle lasers. For foils irradiated by lasers exceeding the blow-out field strength (i.e., capable of fully separating electrons from the ion background), the addition of a second harmonic field results in the stabilization of the foil up to the blow-out intensity. This is then followed by a sharp transition to transparency that essentially occurs in a single optical cycle. During the transition cycle, a dense, nanometer-scale electron bunch is accelerated to relativistic velocities and emits a single, strong attosecond pulse with a peak intensity approaching that of the laser field.
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Intensity noise as a driver for transverse mode instability in fiber amplifiers - Stihler, C.; Jauregui, C.; Kholaif, S.; Limpert, J. (PhotoniX, 2020)
The effect of transverse mode instability (TMI) is currently the main limitation for the further average-power scaling of fiber laser systems with diffraction-limited beam quality. In this work a main driving force for TMI in fiber amplifiers is identified. Our experiments and simulations illustrate that the performance of fiber laser systems in terms of their diffraction-limited output power can be significantly reduced when the pump or seed radiation exhibit intensity noise. This finding emphasizes the fact that the TMI threshold is not only determined by the active fiber but, rather, by the whole system. In the experiment an artificially applied pump intensity-noise of 2.9% led to a reduction of the TMI threshold of 63%, whereas a similar seed intensity-noise decreased it by just 13%. Thus, even though both noise sources have an impact on the TMI threshold, the pump intensity-noise can be considered as the main driver for TMI in saturated fiber amplifiers. Additionally, the work unveils that the physical origin of this behavior is linked to the noise transfer function in saturated fiber amplifiers. With the gained knowledge and the experimental and theoretical results, it can be concluded that a suppression of pump-noise frequencies below 20 kHz could strongly increase the TMI threshold in high-power fiber laser systems.
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Many-electron effects in the hyperfine splitting of lithiumlike ions - Kosheleva, V. P.; Volotka, A. V.; Glazov, D. A.; Fritzsche, S. (Physical Review Research, 2020)
The rigorous QED evaluation of the one- and two-photon exchange corrections to the ground-state hyperfine splitting in Li-like ions is presented for the wide range of nuclear charge number Z = 7-82. The calculations are carried out in the framework of the extended Furry picture, i.e., with the inclusion of the effective local screening potential in the zeroth-order approximation. The interelectronic-interaction contributions of the third and higher orders are taken into account in the framework of the Breit approximation employing the recursive perturbation theory. In comparison to the previous theoretical calculations, the accuracy of the interelectronic-interaction contributions to the ground-state hyperfine splitting in Li-like ions is substantially improved.
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Observing the Importance of the Phase-Volume Effect for Few-Cycle Light-Matter Interactions - Zhang, Y.; Zille, D.; Hoff, D.; Wustelt, P.; W{\"{u}}rzler, D.; M{\"{o}}ller, M.; Sayler, A. M.; Paulus, G. (Physical Review Letters, 2020)
The spatially dependent phase distribution of focused few-cycle pulses, i.e., the focal phase, is much more complex than the well-known Gouy phase of monochromatic beams. As the focal phase is imprinted on the carrier-envelope phase (CEP), for accurate modeling and interpretation of CEP-dependent few-cycle laser-matter interactions, both the coupled spatially dependent phase and intensity distributions must be taken into account. In this Letter, we demonstrate the significance of the focal phase effect via comparison of measurements and simulations of CEP-dependent photoelectron spectra. Moreover, we demonstrate the impact of this effect on few-cycle light-matter interactions as a function of their nonlinear intensity dependence to answer the general question: if, when, and how much should one be concerned about the focal phase?
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Polarization-dependent high-intensity Kapitza-Dirac effect in strong laser fields - B{\"{o}}ning, B.; Paufler, W.; Fritzsche, S. (Physical Review A, 2020)
We study the deflection of photoelectrons in intense elliptically polarized standing light waves, known as the high-intensity Kapitza-Dirac effect. In order to compute the longitudinal momentum transfer to the photoelectron in above-threshold ionization, we utilize a complete description of the quantum dynamics in the spatially dependent field of the standing light wave. We propose experimental conditions under which low-energy photoelectrons can be generated with remarkably high longitudinal momenta that can be controlled via the polarization of the standing wave. We expect that future experimental realizations will provide additional insights into the momentum transfer in intense laser-atom interactions.
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Polarization-Dependent Self-Injection by Above Threshold Ionization Heating in a Laser Wakefield Accelerator - Ma, Y.; Seipt, D.; Hussein, A. E.; Hakimi, S.; Beier, N. F.; Hansen, S. B.; Hinojosa, J.; Maksimchuk, A.; Nees, J.; Krushelnick, K.; Thomas, A. G. R.; Dollar, F. (Physical Review Letters, 2020)
We report on the experimental observation of a decreased self-injection threshold by using laser pulses with circular polarization in laser wakefield acceleration experiments in a nonpreformed plasma, compared to the usually employed linear polarization. A significantly higher electron beam charge was also observed for circular polarization compared to linear polarization over a wide range of parameters. Theoretical analysis and quasi-3D particle-in-cell simulations reveal that the self-injection and hence the laser wakefield acceleration is polarization dependent and indicate a different injection mechanism for circularly polarized laser pulses, originating from larger momentum gain by electrons during above threshold ionization. This enables electrons to meet the trapping condition more easily, and the resulting higher plasma temperature was confirmed via spectroscopy of the XUV plasma emission.
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Post-compression of picosecond pulses into the few-cycle regime - Balla, P.; Wahid, A. B.; Sytcevich, I.; Guo, C.; Viotti, A.-L.; Silletti, l.; Cartella, A.; Ali{{s}}auskas, S.; Tavakol, H.; Grosse-Wortmann, U.; Sch{\"{o}}nberg, A.; Seidel, M.; et al. (Optics Letters, 2020)
In this work, we demonstrate post-compression of 1.2 picosecond laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a singlestage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route towards compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.
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Proton acceleration via the TNSA mechanism using a smoothed laser focus - Afshari, M.; Hornung, J.; Kleinschmidt, A.; Neumayer, P.; Bertini, D.; Bagnoud, V. (AIP Advances, 2020)
In this work, we present the results of an experiment aiming at proton acceleration using a focus with a homogeneous intensity distribution, called smoothed focus. To achieve this goal, we implemented a phase plate before the pre-amplifier of the Petawatt High-Energy Laser for Heavy Ion EXperiments laser facility. The phase plate was used for the first time at a high-power short-pulse laser. Demonstrating a low divergent ion beam was the main goal of this work. Numerical simulations using the particle-in-cell code Extendable PIC Open Collaboration estimated a 2–5 times reduction in the angular divergence of the proton beam using a phase plate due to a smoother sheath at the rear side of the target. However, the reduction in the angular divergence was not sensible according to the experimental data. A positive point is that the spectrum of protons that are generated with the smoothed beam is shifted toward lower energies, provided that the laser absorption is kept in check, compared to the Gaussian proton spectrum. Moreover, the number of protons that are generated with the smoothed beam is higher than the ones generated with the Gaussian beam.
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Ptychography and single-shot nanoscale imaging with plasma-based laser sources - Tuitje, F.; Z{\"{u}}rch, M.; Helk, T.; Gautier, J.; Tissandier, F.; Goddet, J.-P.; Oliva, E.; Guggenmos, A.; Kleineberg, U.; Stiel, H.; Sebban, S.; Spielmann, C. (Springer Proceedings in Physics, 2020)
We report the direct wavefront characterization of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength and monitor the exit of the laser plasma amplifier depending on the arrival time of the seed pulses with respect to pump pulses. For the wavefront measurement in phase and intensity, we used high-resolution ptychography. After propagating the wavefront back to the source, we are able to observe the rear end of the plasma amplifier. We compare the characteristics of the seeded soft X-ray Laser to an unseeded one and find an increasing beam stability and lateral coherence important for lensless imaging techniques.
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Visualization of relativistic laser pulses in underdense plasma - Schwab, M. B.; Siminos, E.; Heinemann, T.; Ullmann, D.; Karbstein, F.; Kuschel, S.; S{\"{a}vert, A. and Yeung, M. and Hollatz, D. and Seidel, A. and Cole, J. and Mangles, S. P. D. and Hidding, B. and Zepf, M. and Skupin, S. and Kaluza, M.C. (Physical Review Accelerators and Beams, 2020)
We present experimental evidence of relativistic electron-cyclotron resonances (RECRs) in the vicinity of the relativistically intense pump laser of a laser wakefield accelerator (LWFA). The effects of the RECRs are visualized by imaging the driven plasma wave with a few-cycle, optical probe in transverse geometry. The probe experiences strong, spectrally dependent and relativistically modified birefringence in the vicinity of the pump that arises due to the plasma electrons’ relativistic motion in the pump’s electromagnetic fields. The spectral birefringence is strongly dependent on the local magnetic field distribution of the pump laser. Analysis and comparison to both 2D and 3D particle-in-cell simulations confirm the origin of the RECR effect and its appearance in experimental and simulated shadowgrams of the laser-plasma interaction. The RECR effect is relevant for any relativistic, magnetized plasma and in the case of LWFA could provide a nondestructive, in situ diagnostic for tracking the evolution of the pump’s intensity distribution with propagation through tenuous plasma.
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Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation - Hofbrucker, J.; Volotka, A. V.; Fritzsche, S. (Scientific Reports, 2020)
We predict breakdown of the electric dipole approximation at nonlinear Cooper minimum in direct two-photon K–shell atomic ionisation by circularly polarised light. According to predictions based on the electric dipole approximation, we expect that tuning the incident photon energy to the Cooper minimum in two-photon ionisation results in pure depletion of one spin projection of the initially bound 1s electrons, and hence, leaves the ionised atom in a fully oriented state. We show that by inclusion of electric quadrupole interaction, dramatic drop of orientation purity is obtained. The low degree of the remaining ion orientation provides a direct access to contributions of the electron-photon interaction beyond the electric dipole approximation in the two-photon ionisation of atoms and molecules. The orientation of the photoions can be experimentally detected either directly by a Stern-Gerlach analyzer, or by means of subsequent Kα fluorescence emission, which has the information about the ion orientation imprinted in the polarisation of the emitted photons.
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HILITE{–}A tool to investigate interactions of matter and light - Stallkamp, N.; Ringleb, S.; Arndt, B.; Kiffer, M.; Kumar, S.; Morgenroth, T.; Paulus, G.G.; Quint, W.; St{\"{o}}hlker, T.; Vogel, M. (X-Ray Spectrometry, 2020)
Detailed investigations of laser–ion interactions require well‐defined ion targets and detection techniques for high‐sensitivity measurements of reaction educts and products. To this end, we have designed and built the High‐Intensity Laser‐Ion Trap Experiment Penning trap setup, which features various ion‐target preparation techniques including selection, cooling, compression, and positioning as well as destructive and non‐destructive measurement techniques to determine the number of stored ions for all charge states individually and simultaneously. We have recently performed first commissioning experiments of ion deceleration and dynamic ion capture with highly charged ion bunches from an electron beam ion source. We have characterized our single‐pass non‐destructive ion counter in detail and were able to determine the ion velocity as well as the number of ions from the signals acquired.
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Inverted field interferometer for measuring the topological charges of optical vortices carried by short pulses - Dimitrov, N.; Zhekova, M.; Paulus, G.; Dreischuh, A. (Optics Communications, 2020)
In this work, we present an improved technique for measuring both the magnitude and sign of the topological charge of input optical vortex beams carried by short laser pulses. Numerical simulations and experimental evidences for the interference signal obtainable at the output of an inverted field interferometer (IFI) valid for both continuous wave and femtosecond optical vortex beams and pulses with an eventual pulse front tilt are in an excellent agreement. An IFI also appears to be a valuable tool for calibrating a built-in variable delay line and for estimating an eventual pulse front tilt of the input ultrashort laser pulses without any realignments. As a trivial side effect, by blocking alternatively one of the two arms of the interferometer, one can use OV beams/pulses of opposite TCs, which are well located in the plane of a desired target, eventually {–} at precisely known time delays.
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Multiple Photodetachment of Carbon Anions via Single and Double Core-Hole Creation - Perry-Sassmannshausen, A.; Buhr, T.; Borovik, A.; Martins, M.; Reinwardt, S.; Ricz, S.; Stock, S.; Trinter, F.; M{\"{u}}ller, A.; Fritzsche, S.; Schippers, S. (Physical Review Letters, 2020)
We report on new measurements of m-fold photodetachment (m=2-5) of carbon anions via K-shell excitation and ionization. The experiments were carried out employing the photon-ion merged-beams technique at a synchrotron light source. While previous measurements were restricted to double detachment (m=2) and to just the lowest-energy K-shell resonance at about 282 eV, our absolute experimental m-fold detachment cross sections at photon energies of up to 1000 eV exhibit a wealth of new thresholds and resonances. We tentatively identify these features with the aid of detailed atomic-structure calculations. In particular, we find unambiguous evidence for fivefold detachment via double K-hole production.
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Opportunities for measurements of astrophysical-relevant alpha-capture reaction rates at CRYRING@ESR - Forstner, O.; Bemmerer, D.; Cowan, T.; Dressler, R.; Junghans, A.; Schumann, D.; St{\"{o}}hlker, T.; Sz{\"{u}}cs, T.; Wagner, A.; Zuber, K. (X-Ray Spectrometry, 2020)
The heavy-ion storage ring CRYRING@ESR has recently been installed and commissioned at GSI as one of the first installations of the upcoming Facility for Antiproton and Ion Research (FAIR). It is designed to store highly charged ions in the energy range between 300?keV/u and about 10?MeV/u. It will incorporate a gas-jet target providing high-density jets of, among other gases, hydrogen and helium. This will allow to study alpha-capture reaction rates of astrophysical interest in the energy range of the Gamow window for core-collapse supernovae. Special interest comes from the long-lived radio-isotope 44Ti (t1/2?=?58.9?years), which is supposed to be produced in the alpha-rich freeze-out during such an event. The nucleosynthesis of this isotope is of great interest, as the amount of material produced can be estimated by direct observation in remnants of recent supernovae. The disagreements between the observations and the estimations from astrophysical models show the need of more experimental data for the production and consumption reactions in the energy range of a core-collapse supernova. In this article, we will describe the proposed method of injecting beams of 44Ti into CRYRING@ESR and performing the actual reaction rate measurements.
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Radiative electron capture to the continuum in U89+ + N2 collisions: Experiment and theory - Hillenbrand, P.-M.; Hagmann, S.; Groshev, M.; Bana{ś}, D.; Benis, E.; Brandau, C.; De Filippo, E.; Forstner, O.; Glorius, J.; Grisenti, R.; Gumberidze, A.; Guo, D.; et al. (Physical Review A, 2020)
For U89+ projectiles colliding at a beam energy of 75.91 MeV/u with a N2 target, we present a coincidence measurement between the cusp electrons emitted under an angle of 0° with respect to the projectile beam and the photons emitted under a polar angle of 90°. This radiative-electron-capture-to-continuum cusp directly probes the theory of electron-nucleus bremsstrahlung up to the high-energy endpoint in inverse kinematics. In the present study, significant improvement with respect to the experimental accuracy has been achieved, resulting in a finer agreement between experimental and theoretical results.
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Studies of equation of state properties of high-energy-density matter generated by intense ion beams at the facility for antiprotons and ion research - Tahir, N. A.; Neumayer, P.; Lomonosov, I. V.; Shutov, A.; Bagnoud, V.; Piriz, A. R.; Piriz, S. A.; Deutsch, C. (Physical Review E, 2020)
The work presented in this paper shows with the help of two-dimensional hydrodynamic simulations that intense heavy-ion beams are a very efficient tool to induce high energy density (HED) states in solid matter. These simulations have been carried out using a computer code BIG2 that is based on a Godunov-type numerical algorithm. This code includes ion beam energy deposition using the cold stopping model, which is a valid approximation for the temperature range accessed in these simulations. Different phases of matter achieved due to the beam heating are treated using a semiempirical equation-of-state (EOS) model. To take care of the solid material properties, the Prandl-Reuss model is used. The high specific power deposited by the projectile particles in the target leads to phase transitions on a timescale of the order of tens of nanosecond, which means that the sample material achieves thermodynamic equilibrium during the heating process. In these calculations we use Pb as the sample material that is irradiated by an intense uranium beam. The beam parameters including particle energy, focal spot size, bunch length, and bunch intensity are considered to be the same as the design parameters of the ion beam to be generated by the SIS100 heavy-ion synchrotron at the Facility for Antiprotons and Ion Research (FAIR), at Darmstadt. The purpose of this work is to propose experiments to measure the EOS properties of HED matter including studies of the processes of phase transitions at the FAIR facility. Our simulations have shown that depending on the specific energy deposition, solid lead will undergo phase transitions leading to an expanded hot liquid state, two-phase liquid-gas state, or the critical parameter regime. In a similar manner, other materials can be studied in such experiments, which will be a very useful addition to the knowledge in this important field of research.
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Towards a determination of absolute cross sections for projectile excitation of hydrogen‐like uranium in collisions with neutral atoms - Weber, G.; Gumberidze, A.; Herdrich, M.; M{\"{a}rtin, R. and Spillmann, U. and Surzhykov, A. and Thorn, D. and Trotsenko, S. and Petridis, N. and Fontes, C. and St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
Recently, the contribution of the generalized Breit interaction to electron impact ionization was identified for the first time in a high‐Z system, namely, hydrogen‐like uranium. This study employed a measurement of the relative population of the j = 1/2 and j = 3/2 states of the L shell by projectile excitation in collision of U91+ with hydrogen and nitrogen targets. However, for a rigorous test of ion–atom collision theory, also the absolute excitation cross sections are of great importance. In the present work, we report on our efforts to extend the previous study to a determination of the absolute projectile excitation cross sections by normalization to the well‐known radiative electron capture process.
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Towards experiments with highly charged ions at HESR - Sanchez, R.; Braeuning-Demian, A.; Glorius, J.; Hagmann, S.; Hillenbrand, P.-M.; Kalinin, A.; K{\"{o}}hler, T.; Litvinov, Y. A.; Petridis, N.; Sanjari, S.; Spillmann, U.; St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
The atomic physics collaboration SPARC is a part of the APPA pillar at the future Facility for Antiproton and Ion Research. It aims at atomic‐physics research across virtually the full range of atomic matter. An emphasis of this contribution are the atomic physics experiments addressing the collision dynamics in strong electro‐magnetic fields as well as the fundamental interactions between electrons and heavy nuclei at the HESR. Here we give a short overview about the central instruments for SPARC experiments at this storage ring.
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Trident process in laser pulses - Dinu, V.; Torgrimsson, G. (Physical Review D, 2020)
We study the trident process in laser pulses. We provide exact numerical results for all contributions, including the difficult exchange term. We show that all terms are in general important for a short pulse. For a long pulse, we identify a term that gives the dominant contribution even if the intensity is only moderately high, a0≳1, which is an experimentally important regime where the standard locally constant field (LCF) approximation cannot be used. We show that the spectrum has a richer structure at a0∼1, compared to the LCF regime a0≫1. We study the convergence to LCF as a0 increases and how this convergence depends on the momentum of the initial electron. We also identify the terms that dominate at high energy.
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10.4 kW coherently combined ultrafast fiber laser - M{\"{u}}ller, M.; Aleshire, C.; Klenke, A.; Haddad, E.; L{\'{e}}gar{\'{e}}, F.; T{\"{u}}nnermann, A.; Limpert, J. (Optics Letters, 2020)
An ultrafast laser delivering 10.4 kW average output power based on a coherent combination of 12 step-index fiber amplifiers is presented. The system emits close-to-transform-limited 254 fs pulses at an 80 MHz repetition rate, and has a high beam quality (M2 ≤ 1.2) and a low relative intensity noise of 0.56% in the frequency range of 1 Hz to 1 MHz. Automated spatiotemporal alignment allows for hands-off operation.
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A magnetic spectrometer for electron‐positron pair spectroscopy in storage rings - Hagmann, S.; Hillenbrand, P.; Litvinov, Y. A.; Spillmann, U.; St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
We report an analysis of electron‐optical properties of a toroidal magnetic sector spectrometer and examine parameters for its implementation in a relativistic heavy‐ion storage ring, for example the High Energy Storage ring (HESR) at the future Facility for Antiproton and Ion Research (FAIR) facility. For studies of free–free pair production in heavy‐ion atom collisions, this spectrometer exhibits very high efficiencies for coincident e+–e− pair spectroscopy over a wide range of momenta of emitted lepton pairs. The high coincidence efficiency of the spectrometer is the key for stringent tests of theoretical predictions for the phase space correlation of lepton vector momenta in free–free pair production.
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Asymptotically safe QED - Gies, H.; Ziebell, J. (European Physical Journal C, 2020)
High-energy completeness of quantum electrodynamics (QED) can be induced by an interacting ultraviolet fixed point of the renormalization flow. We provide evidence for the existence of two of such fixed points in the subspace spanned by the gauge coupling, the electron mass and the Pauli spin-field coupling. Renormalization group trajectories emanating from these fixed points correspond to asymptotically safe theories that are free from the Landau pole problem. We analyze the resulting universality classes defined by the fixed points, determine the corresponding critical exponents, study the resulting phase diagram, and quantify the stability of our results with respect to a systematic expansion scheme. We also compute high-energy complete flows towards the long-range physics. We observe the existence of a renormalization group trajectory that interconnects one of the interacting fixed points with the physical low-energy behavior of QED as measured in experiment. Within pure QED, we estimate the crossover from perturbative QED to the asymptotically safe fixed point regime to occur somewhat above the Planck scale but far below the scale of the Landau pole.
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Atomic processes with twisted electrons - Zaytsev, V.; Surzhykov, A.; Serbo, V.; Kosheleva, V.; Groshev, M.; Yerokhin, V.; Shabaev, V.; St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 2020)
The present status of the fully-relativistic nonperturbative calculations of the fundamental atomic processes with twisted electrons is presented. In particular, the elastic (Mott) scattering, the radiative recombination, and for the very first time, the Bremsstrahlung processes are considered. The electron-ion interaction is accounted for in a nonperturbative manner, that allows obtaining reliable results for heavy systems. We investigate the influence of the of the incoming electron on the angular and polarization properties of the emitted electrons and photons for the elastic and inelastic scattering, respectively. It is found that these properties exhibit a strong dependence on the opening angle of the vortex electron beam in all processes considered.
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Characterisation of ion bunches by a single-pass non-destructive charge counter - Kiffer, M.; Ringleb, S.; Stallkamp, N.; Kumar, S.; Arndt, B.; Vogel, M.; Quint, W.; St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 2020)
Synopsis We present non-destructive single-pass ion bunch detection and characterisation by measuring the induced image charge in a detection electrode. The presented technique allows direct determination of ion kinetic energy, absolute ion number and spatial ion bunch length. We will show the results of corresponding measurements with bunches of low-energy highly charged ions and discuss the minimum detectable number of charges.
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Charge state tailoring of relativistic heavy ion beams for the Gamma Factory project at CERN - Kr{\"{o}}ger, F. M.; Weber, G.; Shevelko, V. P.; Hirlaender, S.; Krasny, M. W.; St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
We present charge‐state evolution studies for Pb⁵⁴⁺ ion beams passing through stripper foils at relativistic energies of 5.9 GeV/u. The purpose of this investigation is to determine the optimum target material and non‐equilibrium thickness for the efficient production of few‐electron lead ions, that is, Pb⁸⁰⁺ and Pb⁸¹⁺, at the present European Organization for Nuclear Research, CERN, accelerator facility at energies as high as 5.9 GeV/u. Based on these predictions, an Al stripper foil has been selected for a proof‐of‐principle measurement in the frame of the Gamma Factory study group. The experimental data confirms a substantial yield of non‐bare Pb ions. In addition, a charge‐state evolution study for the production of Li‐like lead ions Pb⁷⁹⁺ is presented, which will be subject of a follow‐up experiment in the near future.
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Coincident mapping of e+and e-from free-free pair production in a magnetic toroidal lepton spectrometer - Hagmann, S.; Hillenbrand, P.; Litvinov, Y.; Spillmann, U.; St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 2020)
We discuss the electron-optical properties of a toroidal magnetic sector spectrometer and its suitablilty for electron-positron pair spectroscopy in relativistic ion-atom collisions in the future HESR storage ring at FAIR. With the simultaneous mapping of electrons and positrons and geometric invariants in the lepton trajectorties this instrument offers a very high efficiency for studies of vector momentum correlation in free-free pair production.
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Comparative study of strong-field ionization of alkaline-earth-metal atoms - Kang, H.; Chen, S.; Lin, Z.; Chu, W.; Yao, J.; Quan, W.; Chen, J.; Liu, X.; Cheng, Y.; Xu, Z. (Physical Review A, 2020)
We report on a comparative study of strong-field ionization of alkaline-earth-metal atoms by intense femtosecond laser pulses from near-infrared to midinfrared wavelengths. By collecting the ionization signals only produced within the central portion of the laser focus, the focus volume effect is largely reduced and the saturation intensities for different alkaline-earth-metal atoms are reliably determined, which permits us to directly test the strong-field-ionization theories. We demonstrate that the Perelomov-Popov-Terent'ev model accurately predicts the experimental ionization yields and saturation intensities in general for arbitrary values of the Keldysh parameter, while the Ammosov-Delone-Krainov simulations agree with the experiments for the tunneling-ionization regime and also for the regime when the Keldysh parameter is around 1. Our work presents benchmark data for strong-field ionization of alkaline-earth metals over a broad range of laser parameters and confirms the validity of Keldysh's picture for such atoms.
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Concept and simulations of a high-resolution asymmetric von Hamos X-ray spectrometer for CRYRING@ESR electron cooler - Jagodzi{ł}ski, P.; Bana{ś}, D.; Pajek, M.; Warczak, A.; Beyer, H.; Gumberidze, A.; Weber, G.; St{\"{o}}hlker, T.; Trassinelli, M. (Journal of Physics: Conference Series, 2020)
A concept of a high resolution asymmetric von Hamos X-ray spectrometer for the CRYRING@ESR electron cooler is described and its characteristics obtained by ray-tracing Monte-Carlo simulations are presented. The spectrometer will be used to study the QED e-ects in H-like medium-Z ions by measuring the energies of X-rays from radiative recombination of highly charged ions with cooling electrons, with a ppm precision of energy determination.
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Determination of luminosity for in-ring reactions: A new approach for the low-energy domain - Xing, Y.; Glorius, J.; Varga, L.; Bott, L.; Brandau, C.; Br{\"{u}}ckner, B.; Chen, R.; Chen, X.; Dababneh, S.; Davinson, T.; Erbacher, P.; Fiebiger, S.; et al. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2020)
Luminosity is a measure of the colliding frequency between beam and target and it is a crucial parameter for the measurement of absolute values, such as reaction cross sections. In this paper, we make use of experimental data from the ESR storage ring to demonstrate that the luminosity can be precisely determined by modelling the measured Rutherford scattering distribution. The obtained results are in good agreement with an independent measurement based on the x-ray normalization method. Our new method provides an alternative way to precisely measure the luminosity in low-energy stored-beam configurations. This can be of great value in particular in dedicated low-energy storage rings where established methods are difficult or impossible to apply.
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Determination of non-linear refractive index of laser crystals and ceramics via different optical techniques - Lamaign{\`{e}}re, L.; Toci, G.; Patrizi, B.; Vannini, M.; Pirri, A.; Fanetti, S.; Bini, R.; Mennerat, G.; Melninkaitis, A.; Lukas, L.; Hein, J. (Optical Materials: X, 2020)
The exact knowledge of optical material parameters is crucial for laser systems design. Therefore, the work reported herein was dedicated to the determination of an important parameter that is typically not known or only known with insufficient precision: the Kerr coefficient determined by the third order non-linearity, also called the n2-parameter. The optical Kerr effect is responsible for the accumulated nonlinear phase (the B-integral) in high energy laser amplifiers, which often represents a serious limitation. Therefore, the knowledge of n2 is especially required for new types of laser materials. In this paper we report measurements carried out on the widely used optical material Ytterbium-doped Yttrium Aluminium Garnet (Yb:YAG) ceramics. Furthermore, the new Neodymium-doped Calcium Fluoride (Nd:CaF2) crystal was investigated. Specifically, three different approaches have been employed to determine experimentally the nonlinear refractive index of these materials. Thus classical Z-scan technique (at two different wavelengths), the degenerated four waves mixing and the time-resolved digital holography techniques, were compared. These different approaches have permitted the precise measurements of these parameters as well as their dispersion estimations.
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Development of a detector to register low-energy, charge-changed ions from ionization experiments at CRYRING@ESR - Borovik, A.; Weber, G.; Hilbert, V.; Lin, H.; Pf{\"{a}fflein, P. and Zhu, B. and Hahn, C. and Lestinsky, M. and Schippers, S. and St{\"{o}}hlker, T. and Rothhardt, J. (Journal of Physics: Conference Series, 2020)
A detector setup for registering ion species between the poles of a dipole magnet at CRYRING@ESR has been developed. It is based on a scintillator delivering light via a quartz light guide onto a semiconductor photomultiplier. The detector is capable of operating in a strong magnetic field. It can be swiftly retracted from the exposition area during the beam injection into the ring and repositioned back for the measurement cycle to avoid unnecessary exposition and, thus, to increase the scintillator life time.
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Discrete dispersion scan setup for measuring few-cycle laser pulses in the mid-infrared - Geib, N.; Hollinger, R.; Haddad, E.; Herrmann, P.; L{\'{e}}gar{\'{e}}, F.; Pertsch, T.; Spielmann, C.; Z{\"{u}}rch, M.; Eilenberger, F. (Optics Letters, 2020)
In this work, we demonstrate a discrete dispersion scan scheme using a low number of flat windows to vary the dispersion of laser pulses in discrete steps. Monte Carlo simulations indicate that the pulse duration can be retrieved accurately with less than 10 dispersion steps, which we verify experimentally by measuring few-cycle pulses and material dispersion curves at 3 and 10 µm wavelength. This minimal measuring scheme using only five optical components without the need for linear positioners and interferometric alignment can be readily implemented in many wavelength ranges and situations.
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Elastic photon scattering on hydrogenic atoms near resonances - Samoilenko, D.; Volotka, A.; Fritzsche, S. (Atoms, 2020)
Scattering of light on relativistic heavy ion beams is widely used for characterizing and tuning the properties of both the light and the ion beam. Its elastic component-Rayleigh scattering-is investigated in this work for photon energies close to certain electronic transitions because of its potential usage in the Gamma Factory initiative at CERN. The angle-differential cross-section, as well as the degree of polarization of the scattered light are investigated for the cases of 1s - 2p1/2 and 1s - 2p3/2 resonance transitions in H-like lead ions. In order to gauge the validity and uncertainty of frequently used approximations, we compare different methods. In particular, rigorous quantum electrodynamics calculations are compared with the resonant electric-dipole approximation evaluated within the relativistic and nonrelativistic formalisms. For better understanding of the origin of the approximation, the commonly used theoretical approach is explained here in detail. We find that in most cases, the nonrelativistic resonant electric-dipole approximation fails to describe the properties of the scattered light. At the same time, its relativistic variant agrees with the rigorous treatment within a level of 10% to 20%. These findings are essential for the design of an experimental setup exploiting the scattering process, as well as for the determination of the scattered light properties.
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Enhancement of the laser-driven proton source at PHELIX - Hornung, J.; Zobus, Y.; Boller, P.; Brabetz, C.; Eisenbarth, U.; K{\"{u}}hl, T.; Major, Zs.; Ohland, J.; Zepf, M.; Zielbauer, B.; Bagnoud, V. (High Power Laser Science and Engineering, 2020)
We present a study of laser-driven ion acceleration with micrometre and sub-micrometre thick targets, which focuses on the enhancement of the maximum proton energy and the total number of accelerated particles at the PHELIX facility. Using laser pulses with a nanosecond temporal contrast of up to and an intensity of the order of, proton energies up to 93 MeV are achieved. Additionally, the conversion efficiency at incidence angle was increased when changing the laser polarization to p, enabling similar proton energies and particle numbers as in the case of normal incidence and s-polarization, but reducing the debris on the last focusing optic.
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Few-cycle fs-pumped NOPA with passive ultrabroadband spectral shaping - Tamer, I.; Hellwing, M.; Azamoum, Y.; Hornung, M.; Keppler, S.; Schorcht, F.; Hein, J.; Kaluza, M. (Optics Express, 2020)
A compact, femtosecond-pumped noncollinear optical parametric amplifier (NOPA) is presented with a passive spectral shaping technique, employed to produce a flat-top-like ultrabroadband output spectrum. The NOPA is pumped by a dedicated 2 mJ, 120 fs Yb3+- based CPA system, which generates both the second harmonic pump pulse and white light supercontinuum as the signal pulse. A chirped mirror pair pre-compensates the material GVD within the optical path of the signal pulse to produce a near-FTL pulse duration at the OPA crystal output. By optimizing both the pump/signal cross angle and the pump/signal delay, the 40 cm × 40 cm footprint, single-pass, fs-pumped, direct NOPA (non-NOPCPA) system generates a record 20 μJ, 11 fs pulses at 820 nm central wavelength with a bandwidth of 230 nm FWHM, to be used as an ultrashort optical probe pulse for relativistic laser-plasma interactions at the petawatt-class POLARIS laser system.
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Fiber laser-driven gas plasma-based generation of THz radiation with 50-mW average power - Buldt, J.; Mueller, M.; Stark, H.; Jauregui, C.; Limpert, J. (Applied Physics B, 2020)
We present on THz generation in the two-color gas plasma scheme driven by a high-power, ultrafast fiber laser system. The applied scheme is a promising approach for scaling the THz average power but it has been limited so far by the driving lasers to repetition rates up to 1 kHz. Here, we demonstrate recent results of THz generation operating at a two orders of magnitude higher repetition rate. This results in a unprecedented THz average power of 50 mW. The development of compact, table-top THz sources with high repetition rate and high field strength is crucial for studying nonlinear responses of materials, particle acceleration or faster data acquisition in imaging and spectroscopy.
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Flexible all-PM NALM Yb:fiber laser design for frequency comb applications: Operation regimes and their noise properties - Mayer, A.; Grosinger, W.; Fellinger, J.; Winkler, G.; Perner, L.; Droste, S.; Salman, S.; Li, C.; Heyl, C.; Hartl, I.; Heckl, O. (Optics Express, 2020)
We present a flexible all-polarization-maintaining (PM) mode-locked ytterbium (Yb):fiber laser based on a nonlinear amplifying loop mirror (NALM). In addition to providing detailed design considerations, we discuss the different operation regimes accessible by this versatile laser architecture and experimentally analyze five representative mode-locking states. These five states were obtained in a 78-MHz configuration at different intracavity group delay dispersion (GDD) values ranging from anomalous (-0.035 ps2) to normal (+0.015 ps2). We put a particular focus on the characterization of the intensity noise as well as the free-running linewidth of the carrier-envelope-offset (CEO) frequency as a function of the different operation regimes. We observe that operation points far from the spontaneous emission peak of Yb ( 1030 nm) and close to zero intracavity dispersion can be found, where the influence of pump noise is strongly suppressed. For such an operation point, we show that a CEO linewidth of less than 10-kHz at 1 s integration can be obtained without any active stabilization.
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g factor of the [(1s)2(2s)22p]2P3/2 state of middle-Z boronlike ions - Agababaev, V.; Glazov, D.; Volotka, A.; Zinenko, D.; Shabaev, V.; Plunien, G. (X-Ray Spectrometry, 2020)
Theoretical g-factor calculations for the first excited 2P3/2 state of boronlike ions in the range Z=10–20 are presented and compared with the previously published values. The first-order interelectronic-interaction contribution is evaluated within the rigorous quantum electrodynamics (QED) approach in the effective screening potential. The second-order contribution is considered within the Breit approximation. The QED and nuclear recoil corrections are also taken into account.
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High numerical aperture Hartmann wave front sensor for extreme ultraviolet spectral range - Li, L.; Koliyadu, J.; Donnelly, H.; Alj, D.; Delmas, O.; Ruiz-Lopez, M.; de la Rochefoucauld, O.; Dovillaire, G.; Fajardo, M.; Zhou, C.; Ruan, S.; Dromey, B.; et al. (Optics Letters, 2020)
We present a novel, to the best of our knowledge, Hartmann wave front sensor for extreme ultraviolet (EUV) spectral range with a numerical aperture (NA) of 0.15. The sensor has been calibrated using an EUV radiation source based on gas high harmonic generation. The calibration, together with simulation results, shows an accuracy beyond λ/39 root mean square (rms) at λ = 32 nm. The sensor is suitable for wave front measurement in the 10 nm to 45 nm spectral regime. This compact wave front sensor is high-vacuum compatible and designed for in situ operations, allowing wide applications for up-to-date EUV sources or high-NA EUV optics.
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High-power ytterbium-doped fiber laser delivering few-cycle, carrier-envelope phase-stable 100 µJ pulses at 100 kHz - Shestaev, E.; Hoff, D.; Sayler, A. M.; Klenke, A.; H{\"{a}drich, S. and Just, F. and Eidam, T. and J{\'{o}}j{\'{a}}rt, P. and V{\'{a}}rallyay, Z. and Osvay, K. and Paulus, G.G. and T{\"{u}}nnermann, A. and Limpert, J. (Optics Letters, 2020)
We present a carrier-envelope phase (CEP)-stable Yb-doped fiber laser system delivering 100 µJ few-cycle pulses at a repetition rate of 100 kHz. The CEP stability of the system when seeded by a carrier-envelope offset-locked oscillator is 360 mrad, as measured pulse-to-pulse with a stereographic above-threshold ionization (stereo-ATI) phase meter. Slow CEP fluctuations have been suppressed by implementing a feedback loop from the phase meter to the pulse picking acousto-optic modulator. To the best of our knowledge, this is the highest CEP stability achieved to date with a fiber-based, high-power few-cycle laser.
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High-precision X-ray spectroscopy of Fe ions in an EBIT using a micro-calorimeter detector: First results - Herdrich, M.; Fleischmann, A.; Hengstler, D.; Allgeier, S.; Enss, C.; Trotsenko, S.; Morgenroth, T.; Schuch, R.; Weber, G.; St{\"{o}}hlker, T. (X-Ray Spectrometry, 2020)
A micro-calorimeter X-ray detector of the maXs-30 type was used to record the X-ray radiation from Fe ions, being produced in the S-EBIT-I electron beam ion trap at the site of GSI. The resulting spectra demonstrate the superior energy resolving power of micro-calorimeter detectors compared with conventional semiconductor detectors. The experiment serves as another proof of principle for the application of calorimeters as dedicated high-resolution X-ray spectrometers at an ion facility. Together with the development of an improved analysis algorithm for online readout, these results present a step towards the use of maXs-type detectors as standard instrumentation at GSI/FAIR.
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High-resolution wavelength-dispersive spectroscopy of K-shell transitions in hydrogen-like gold - Gassner, T.; Gumberidze, A.; Trassinelli, M.; Hess, R.; Spillmann, U.; Bana{ś}, D.; Blumenhagen, K.-H.; Bosch, F.; Brandau, C.; Chen, W.; Dimopoulou, C.; F{\"{o}}rster, E.; et al. (X-Ray Spectrometry, 2020)
We present a measurement of K‐shell transitions in H‐like gold (Au78+) using specially developed transmission type crystal spectrometers combined with Ge(i) microstrip detectors. The experiment has been carried out at the Experimental Storage Ring at GSI in Darmstadt. This is a first high‐resolution wavelength‐dispersive measurement of a K‐shell transition in a high‐Z H‐like ion, thus representing an important milestone in this field. Ideas on possible future improvements are discussed as well.
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HILITE-A well-defined ion target for laser experiments - Stallkamp, N.; Ringleb, S.; Arndt, B.; Kiffer, M.; Kumar, S.; Paulus, G.; Quint, W.; St{\"{o}}hlker, T.; Vogel, M. (Journal of Physics: Conference Series, 2020)
We present a Penning-trap-based setup for the study of light-matter interactions in the high-power and/or high-intensity laser regime, such as multi-photon ionization and field ionization. The setup applies ioncloud formation techniques to highly charged ions to the end of specific target preparation, as well as nondestructive detection techniques to identify and quantify the interaction educts and products.
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Impact parameter sensitive study of inner-shell atomic processes in Xe54+, Xe52+ → Xe collisions - Gumberidze, A.; Kozhuharov, C.; Zhang, R.; Trotsenko, S.; Kozhedub, Y.; Du, R.; Bois, H.; Beyer, F.; Blumenhagen, K.-H.; Brandau, C.; Br{\"{a}uning-Demian, A. and Chen, W. and Forstner, O. and Gao, B. and Gassner, T. and Grisenti, R. and Hagmann, S. and Hillenbrand, P.-M. and Indelicato, P. and Kumar, A. and Lestinsky, M. and Litvinov, Y. and Petridis, N. and Schury, D. and Spillmann, U. and Trageser, C. and Trassinelli, M. and Tu, X. and St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 2020)
In this work, we present a pilot experiment in the experimental storage ring (ESR) at GSI devoted to impact parameter sensitive studies of inner shell atomic processes for bare and He-like xenon ions (Xe54+, Xe52+) colliding with neutral xenon gas atoms. The projectile and target x-rays have been measured at different observation angles for all impact parameters as well as for the impact parameter range of ∼35 - 70 fm.
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Lifetime measurements of ultrashort-lived excited states in Be-like ions - Rothhardt, J.; Bilal, M.; Beerwerth, R.; Volotka, A.; Hilbert, V.; St{\"{o}}hlker, T.; Fritzsche, S.; Limpert, J. (X-Ray Spectrometry, 2020)
We propose to measure the lifetime of short-lived excited states in highly charged ions by pump-probe experiments. Utilizing two synchronized and delayed Femtosecond pulses allows accessing these lifetimes with Femtosecond precision. Such measurements could provide sensitive tests of state-of-the art atomic structure calculations beyond the capabilities of established methods.
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Nonlinear Cooper minimum as a precise tool for understanding multiphoton photoionization - Hofbrucker, J.; Volotka, A. V.; Fritzsche, S. (Journal of Physics: Conference Series, 2020)
A new approach to accurately assess multiphoton ionization is suggested. Vanishing of the dominant ionization channel in nonresonant (direct) multiphoton ionization is predicted for a specific incident photon energy. The exact energy position of such nonlinear Cooper minimum can be accurately measured and requires calculations of the complete electronic spectrum. Measurements of various observables at these photon energies are desirable for further evaluation of theoretical calculations at hitherto unreachable accuracy.
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Nonlinearly charged dyonic black holes - Panahiyan, S. (Nuclear Physics B, 2020)
In this paper, we investigate the thermodynamics of dyonic black holes in the presence of Born-Infeld electromagnetic field. We show that electric-magnetic duality reported for dyonic solutions with Maxwell field is omitted in case of Born-Infeld generalization. We also confirm that generalization to nonlinear field provides the possibility of canceling the effects of cosmological constant. This is done for nonlinearity parameter with 10−33 eV2 order of magnitude which is high nonlinearity regime. In addition, we show that for small electric/magnetic charge and high nonlinearity regime, black holes would develop critical behavior and several phases. In contrast, for highly charged case and Maxwell limits (small nonlinearity), black holes have one thermal stable phase. We also find that the pressure of the cold black holes is bounded by some constraints on its volume while hot black holes' pressure has physical behavior for any volume. In addition, we report on possibility of existences of triple point and reentrant of phase transition in thermodynamics of these black holes. Finally, we show that if electric and magnetic charges are identical, the behavior of our solutions would be Maxwell like (independent of nonlinear parameter and field). In other words, nonlinearity of electromagnetic field becomes evident only when these black holes are charged magnetically and electrically different.
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Nonsequential double ionization of alkaline-earth metal atoms by intense mid-infrared femtosecond pulses - Kang, H.; Chen, S.; Chu, W.; Yao, J.; Chen, J.; Jun Liu, X.; Cheng, Y.; Xu, Z. (Optics Express, 2020)
A systematic study of nonsequential double ionization (NSDI) of alkaline-earth metal atoms with mid-infrared femtosecond pulses is reported. We find that the measured NSDI yield shows a strong target dependence and it is more suppressed for alkaline-earth metal with higher ionization potential. The observation is attributed to the differences in the recollision induced excitation and ionization cross sections of alkaline-earth metals. This work indicates that NSDI of alkaline-earth metals can be generally understood within recollision picture and sheds light on ultrafast control of electron correlation and dynamics of ionic excited states during NSDI of atoms with complex structures.
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Nuclear physics research at heavy ion accelerators: Precision studies with stored and cooled exotic nuclei - Litvinov, Y.; St{\"{o}}hlker, T.; Ma, X.; Zhang, Y.; Yamaguchi, T. (Journal of Physics: Conference Series, 2020)
This contribution is based on the plenary presentation at the 14th International Conference on Heavy Ion Accelerator Technology (HIAT-2018) in Lanzhou, China. Heavy-ion storage rings offer unparalleled opportunities for precision experiments in the realm of nuclear structure, atomic physics and astrophysics. A brief somewhat biased review of the presently ongoing research programs is given as well as the future projects are outlined. The limited space does not allow for detailed description of individual experiments, which shall - to some extent - be compensated by extended bibliography.
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Performance of a scintillator-based ion detector for CRYRING@ESR - Menz, E.; Hahn, C.; Pf{\"{a}fflein, P. and Weber, G. and St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 2020)
A detector based on the scintillator material YAP:Ce and capable of counting single ions is presented. The detector consists of a YAP:Ce crystal and a light guide operating in ultra high vacuum and a conventional photomultiplier outside the vacuum. The crystal demonstrated the necessary radiation hardness against heavy ion irradiation. The detector has been commissioned at CRYRING@ESR and its detection capabilities have been confirmed with beam from the local source.
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Photoionization of low-charged silicon ions - Buhr, T.; Stock, S. O.; Perry-Sassmannshausen, A.; Reinwardt, S.; Martins, M.; Ricz, S.; Mueller, A.; Fritzsche, S.; Schippers, S. (Journal of Physics: Conference Series, 2020)
Single and multiple photoionization of Si1+, Si2+, and Si3+ ions have been investigated near the silicon K-edge using the PIPE setup at beamline P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. Pronounced resonance structures are observed for all ions which are associated with excitation or ionization of a K-shell electron. The experimental cross sections are compared with results from theoretical calculations.
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Plasma-environment effects on K lines of astrophysical interest: III. IPs, K thresholds, radiative rates, and Auger widths in Fe IX - Fe XVI - Deprince, J.; Bautista, M.; Fritzsche, S.; Garc{\'{i}}a, J.; Kallman, T.; Mendoza, C.; Palmeri, P.; Quinet, P. (Astronomy and Astrophysics, 2020)
Aims. In the context of black-hole accretion disks, we aim to compute the plasma-environment effects on the atomic parameters used to model the decay of K-vacancy states in moderately charged iron ions, namely Fe IX - Fe XVI. Methods. We used the fully relativistic multiconfiguration Dirac-Fock method approximating the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-H{\"{u}}ckel potential. Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges 105-107 K and 1018-1022 cm-3. Conclusions. This study confirms that the high-resolution X-ray spectrometers onboard the future XRISM and Athena space missions will be capable of detecting the lowering of the K edges of these ions due to the extreme plasma conditions occurring in accretion disks around compact objects.
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Polarization dependent multiphoton absorption in ZnO thin films - Hollinger, R.; Gupta, D.; Zapf, M.; Karst, M.; R{\"{o}}der, R.; Uschmann, I.; Reisl{\"{o}}hner, U.; Kartashov, D.; Ronning, C.; Spielmann, C. (Journal of Physics D: Applied Physics, 2020)
We present a simple non-destructive approach for studying the polarization dependence of nonlinear absorption processes in semiconductors. The method is based on measuring the yield of the near UV photoluminescence as a function of polarization and intensity of femtosecond laser pulses. In particular, we investigated the polarization dependence of three photon laser absorption in intrinsic and Al-doped ZnO thin films. Both specimen show stronger emission for linearly polarized excitation compared to circular polarization. The ratios for the three-photon absorption coefficients are about 1.8 and independent of the doping. It is shown that Al-doped films have lower threshold for stimulated emission in comparison to the intrinsic films.
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Position sensitive resonant Schottky cavities for heavy ion storage rings - Dmytriiev, D.; Sanjari, M.; Litvinov, Y.; St{\"{o}}hlker, T. (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2020)
Resonant Schottky pick-up cavities are sensitive beam monitors. They are indispensable for the beam diagnostics in storage rings. Apart from their applications in the measurements of beam parameters, they can be used in nondestructive in-ring decay studies of radioactive ion beams. In addition, position sensitive Schottky pick-up cavities enhance precision in the isochronous mass measurement technique. The goal of this work is to construct and test such a position sensitive cavity (e.g. Schottky detector) based on previous theoretical calculations and simulations. These cavities will allow measurement of position using the monopole mode using a non-circular(elliptic) geometry. This information can be further analyzed to increase the performance in isochronous mass spectrometry. A brief description of the detector system from elliptical and cylindrical cavities is described in this work.
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Probing Vacuum Polarization Effects with High-Intensity Lasers - Karbstein, F. (Particles, 2020)
These notes provide a pedagogical introduction to the theoretical study of vacuum polarization effects in strong electromagnetic fields as provided by state-of-the-art high-intensity lasers. Quantum vacuum fluctuations give rise to effective couplings between electromagnetic fields, thereby supplementing Maxwell’s linear theory of classical electrodynamics with nonlinearities. Resorting to a simplified laser pulse model, allowing for explicit analytical insights, we demonstrate how to efficiently analyze all-optical signatures of these effective interactions in high-intensity laser experiments. Moreover, we highlight several key features relevant for the accurate planning and quantitative theoretical analysis of quantum vacuum nonlinearities in the collision of high-intensity laser pulses.
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Production of 100-TW single attosecond x-ray pulse - Xu, X.; Zhang, Y.; Zhang, H.; Lu, H.; Zhou, W.; Zhou, C.; Dromey, B.; Zhu, S.; Zepf, M.; He, X.; Qiao, B. (Optica, 2020)
Attosecond light sources have provided insight into the fastest atomic-scale electronic dynamics. True attosecond-pump–attosecond-probe experiments require a single attosecond pulse at high intensity and large photon energy, a challenge that has yet to be conquered. Here we show 100-TW single attosecond x-ray pulses with unprecedented intensity of 1021 W/cm2 and duration 8.0 as can be produced by intense laser irradiation of a capacitor-nanofoil target composed of two separate nanofoils. In the interaction, a strong electrostatic potential develops between the two foils, which drags electrons out of the second foil and piles them up in vacuum, forming an ultradense relativistic electron nanobunch. This nanobunch reaches both high density and high energy in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single, intense attosecond pulse. Such a pulse enables the capture and control of electron motion at the picometer–attosecond scale.
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Simplified design of optical elements for filled-aperture coherent beam combination - Aleshire, C.; Steinkopff, A.; Jauregui, C.; Klenke, A.; T{\"{u}}nnermann, A.; Limpert, J. (Optics Express, 2020)
A simplification strategy for segmented mirror splitters (SMS) used as beam combiners is presented. These devices are useful for compact beam division and the combination of linear and 2-D arrays. However, the standard design requires unique thin-film coating sections for each input beam; thus, potential for scaling to high beam-counts is limited due to manufacturing complexity. Taking advantage of the relative insensitivity of the beam combination process to amplitude variations, numerical techniques are used to optimize highly simplified designs with only one, two or three unique coatings. It is demonstrated that with correctly chosen coating reflectivities, the simplified optics are capable of high combination efficiency for several tens of beams. The performance of these optics as beam splitters in multicore fiber amplifier systems is analyzed, and inhomogeneous power distribution of the simplified designs is noted as a potential source of combining loss in such systems. These simplified designs may facilitate further scaling of filled-aperture coherently combined systems in linear array or 2-D array formats.
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Simulation of geodesic trajectory of charged BTZ black holes in massive gravity - Hendi, S.; Tavakkoli, A.; Panahiyan, S.; Panah, B.; Hackmann, E. (European Physical Journal C, 2020)
In order to classify and understand structure of the spacetime, investigation of the geodesic motions of massive and massless particles is a key tool. So the geodesic equation is a central equation of gravitating systems and the subject of geodesics in the black hole dictionary attracted much attention. In this paper, we give a full description of geodesic motions in three-dimensional spacetime. We investigate the geodesics near charged BTZ black holes and then generalize our prescriptions to the case of massive gravity. We show that electric charge is a critical parameter for categorizing the geodesic motions of both lightlike and timelike particles. In addition, we classify the type of geodesics based on the particle properties and geometry of spacetime.
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Soft x-ray high order harmonic generation from high power ultrafast thulium-doped fiber lasers - Gebhardt, M.; Heuermann, T.; Gaida, C.; Wang, Z.; Lenski, M.; Klas, R.; Kirsche, A.; Liu, C.; H{\"{a}drich, S. and Jauregui, C. and others, . (Compact EUV { &} X-ray Light Sources, 2020)
We report on soft x-ray HHG driven by a thulium-doped fiber laser. It is the first time that a photon energy cut-off 400 eV has been demonstrated using this highly scalable laser technology.
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Status of CRYRING@ESR and preparations for first experiments - Lestinsky, M.; Andelkovic, Z.; Bai, M.; Br{\"{a}uning-Demian, A. and Chetvertkova, V. and Fedotova, S. and Geithner, O. and Geithner, W. and Gorda, O. and Herfurth, F. and Kalinin, A. and K{\"{a}llberg, A. and Litvinov, S. and Menz, E. and Mohr, K. and Sanchez, R. and St{\"{o}}hlker, T. and Vorobjev, G. and Weinrich, U. (Journal of Physics: Conference Series, 2020)
CRYRING was moved from Stockholm to Darmstadt, modernized and integrated into the GSI/FAIR beamline topology behind ESR. As CRYRING@ESR, it will receive and store heavy, highly charged ions from all species the present accelerator chain is capable of producing. An extensive research program on low-energy atomic collisions, spectroscopy and nuclear reactions was proposed. The facility is gradually completing commissioning, ion beams from the local injector branch have already been stored and prototype experiments performed. We present the machine status and highlight some planned experiments.
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Strong-field laser-induced fragmentation of small molecules from fast to slow - Wustelt, P.; K{\"{u}}bel, M.; Paulus, G.; Sayler, A. (Advances in Atomic, Molecular and Optical Physics, 2020)
The structure and dynamics of molecules are governed by the electric forces acting between electrons and nuclei. Intense, ultrashort laser pulses offer the possibility to manipulate these forces, on the time scales relevant for the motion of a molecule's constituents. Thus, laser fields can act, not only as a mechanism to trigger molecular dynamics, but also controlling them. The fragmentation patterns that result from the interaction testify to the laser-induced processes occurring in the molecule. In this review, we examine how a laser addresses the different degrees of freedom of a molecule, from electronic excitation to vibrations of nuclei, to rotations of the molecule. We will focus the discussion on the most fundamental systems, particularly H2+, H2, and HeH+. These simple systems allow for accurate theoretical analysis of experimental results, and extrapolation of the conclusions to more complex systems. Since some of the most fundamental molecules, such as HeH+ and H3+ do not exist in the neutral form, we put an emphasis on experiments starting from molecular ions, but do not restrict the discussion to these. Strong-field interactions of small molecules are a test ground, not only for experimental but also for theoretical methods. The joint effort of the two scientific disciplines have delivered deep insights into fundamental concepts of molecular science. The recent developments of novel laser sources with longer wavelength, higher peak power, or repetition rates, as well as more complex targets and detection schemes, promise that the field will remain highly relevant in the decades to come.
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Temperature dependent spectroscopic study of Yb3+-doped KG(WO4)2, KY(WO4)2, YAlO3 and YLiF4 for laser applications - K{\"{o}}rner, J.; Kr{\"{u}}ger, M.; Reiter, J.; M{\"{u}}nzer, A.; Hein, J.; Kaluza, M. (Optical Materials Express, 2020)
We present a study on temperature dependent spectroscopic data for Yb:KGW, Yb:KYW and Yb:YLF between 80K and 280K and Yb:YAP between 100K and 300 K. Absorption and emission cross sections are determined. The latter ones are obtained by using a combination of the McCumber relation and the F{\"{u}}chtbauer-Ladenburg equation. Fluorescence lifetimes are measured within a setup optimized for the suppression of re-absorption and compared to the radiative lifetimes calculated from the previously determined cross sections to cross check the validity of the measurements. The cross sections are evaluated with regard to the materials' potential for supporting the generation of ultra-short laser pulses, low quantum defect lasing and requirements for suitable diode laser pump sources.
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The Gamma Factory Project at CERN: a New Generation of Research Tools Made of Light - P{ł}aczek, W.; Abramov, A.; Alden, S. E.; Alemany Fernandez, R.; Antsiferov, P. S.; Apyan, A.; Bartosik, H.; Bessonov, E. G.; Biancacci, N.; Bieron, J.; Bogacz, A.; Bosco, A.; et al. (Acta Physica Polonica B, 2020)
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The low energy beamline of the FISIC experiment: Current status of construction and performance - Schury, D.; M{\'{e}}ry, A.; Ramillon, J.; Adoui, L.; Chesnel, J.-Y.; L{\'{e}}vy, A.; Mac{\'{e}}, S.; Prigent, C.; Rangama, J.; Rousseau, P.; Steydli, S.; Trassinelli, M.; et al. (Journal of Physics: Conference Series, 2020)
Ion-ion collisions between slow (kev/u) and fast (MeV/u) ions play an important role in for example astrophysical or inertial fusion plasmas as well as in ion-matter interaction. In this regime the energy transfer is maximum, as all primary electronic processes reach their maximum. At the same time up to today no reliable experimental data exists while being difficult to treat accurately by theory. We present the current status and performance of the low energy beam-line of the FISIC experiment which aims at filling in the blanks in this regime.
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Towards background-free studies of capture reactions in a heavy-ion storage ring - Varga, L.; Blaum, K.; Davinson, T.; Glorius, J.; Jurado, B.; Langer, C.; Lederer-Woods, C.; Litvinov, Y.; Reifarth, R.; Slavkovsk{\'{a}}, Z.; St{\"{o}}hlker, T.; Woods, P.; et al. (Journal of Physics: Conference Series, 2020)
Stored and cooled highly-charged ions offer unprecedented capabilities for precision studies in realm of atomic-, nuclear-structure and astrophysics. In context of the latter, after the successful investigation of the cross section of 96Ru(p,γ) in 2009, in 2016 the first measurement of the 124Xe(p,γ)125Cs reaction was performed at the Experimental Storage Ring (ESR) at GSI.
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Transverse mode instability - Jauregui, C.; Stihler, C.; Limpert, J. (Advances in Optics and Photonics, 2020)
This work presents a review on the effect of transverse mode instability in highpower fiber laser systems and the corresponding investigations led worldwide over the past decade. This paper includes a description of the experimental observations and the physical origin of this effect, as well as some of the proposed mitigation strategies.
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Controllable beam reshaping by mixing square-shaped and hexagonal optical vortex lattices - Stoyanov, L.; Maleshkov, G.; Zhekova, M.; Stefanov, I.; Paulus, G.; Dreischuh, A. (Scientific Reports, 2019)
In the present work we show experimentally and by numerical calculations a substantial far-field beam reshaping by mixing square-shaped and hexagonal optical vortex (OV) lattices composed of vortices with alternatively changing topological charges. We show that the small-scale structure of the observed pattern results from the OV lattice with the larger array node spacing, whereas the large-scale structure stems from the OV lattice with the smaller array node spacing. In addition, we demonstrate that it is possible to host an OV, a one-dimensional, or a quasi-two-dimensional singular beam in each of the bright beams of the generated focal patterns. The detailed experimental data at different square-to-hexagonal vortex array node spacings shows that this quantity could be used as a control parameter for generating the desired focused structure. The experimental data are in excellent agreement with the numerical simulations.
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High-flux ultrafast extreme-ultraviolet photoemission spectroscopy at 18.4 MHz pulse repetition rate - Saule, T.; Heinrich, S.; Sch{\"{o}}tz, J.; Lilienfein, N.; H{\"{o}}gner, M.; DeVries, O.; Pl{\"{o}}tner, M.; Weitenberg, J.; Esser, D.; Schulte, J.; Russbueldt, P.; Limpert, J.; et al. (Nature Communications, 2019)
Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 x 10(5) photons per pulse in the 25-to-60-eV range, releasing 1 x 10(10) photoelectrons per second from a 10-mu m-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology.
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Implementation of a phase plate for the generation of homogeneous focal-spot intensity distributions at the high-energy short-pulse laser facility PHELIX - Bagnoud, V.; Hornung, J.; Afshari, M.; Eisenbarth, U.; Brabetz, C.; Major, Z.; Zielbauer, B. (High Power Laser Science and Engineering, 2019)
We propose and demonstrate the use of random phase plates (RPPs) for high-energy sub-picosecond lasers. Contrarily to previous work related to nanosecond lasers, an RPP poses technical challenges with ultrashort-pulse lasers. Here, we implement the RPP near the beginning of the amplifier and image-relay it throughout the laser amplifier. With this, we obtain a uniform intensity distribution in the focus over an area 1600 times the diffraction limit. This method shows no significant drawbacks for the laser and it has been implemented at the PHELIX laser facility where it is now available for users.
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Intense attosecond pulses carrying orbital angularmomentum using laser plasma interactions - Wang, J. W.; Zepf, M.; Rykovanov, S. (Nature Communications, 2019)
Light beams with helical phase-fronts are known to carry orbital angular momentum (OAM) and provide an additional degree of freedom to beams of coherent light. While OAM beams can be readily derived from Gaussian laser beams with phase plates or gratings, this is far more challenging in the extreme ultra-violet (XUV), especially for the case of high XUV intensity. Here, we theoretically and numerically demonstrate that intense surface harmonics carrying OAM are naturally produced by the intrinsic dynamics of a relativistically intense circularly-polarized Gaussian beam (i.e. non-vortex) interacting with a target at normal incidence. Relativistic surface oscillations convert the laser pulses to intense XUV harmonic radiation via the well-known relativistic oscillating mirror mechanism. We show that the azimuthal and radial dependence of the harmonic generation process converts the spin angular momentum of the laser beam to orbital angular momentum resulting in an intense attosecond pulse (or pulse train) with OAM.
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Near L-edge Single and Multiple Photoionization of Triply Charged Iron Ions - Beerwerth, R.; Buhr, T.; Perry-Sassmannshausen, A.; Stock, S. O.; Bari, S.; Holste, K.; Kilcoyne, A. L. D.; Reinwardt, S.; Ricz, S.; Savin, D. W.; Schubert, K.; Martins, M.; et al. (The Astrophysical Journal, 2019)
Relative cross sections for m-fold photoionization (m = 1,[…], 5) of Fe3+ by single-photon absorption were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operated at DESY in Hamburg, Germany. The photon energies used spanned the range of 680–950 eV, covering both the photoexcitation resonances from the 2p and 2s shells, as well as the direct ionization from both shells. Multiconfiguration Dirac–Hartree–Fock (MCDHF) calculations were performed to simulate the total photoexcitation spectra. Good agreement was found with the experimental results. These computations helped to assign several strong resonance features to specific transitions. We also carried out Hartree–Fock calculations with relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, we performed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the 2p and 2s shells of Fe3+. Our theoretically predicted charge-state fractions are in good agreement with the experimental results, representing a substantial improvement over previous theoretical calculations. The main reason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of several configurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, this additional shake-down transition of a (sub)valence electron is required to gain the necessary energy for the release of the Auger electron.
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Quantitative phase contrast imaging of a shock-wave with a laser-plasma based X-ray source - Barbato, F.; Atzeni, S.; Batani, D.; Bleiner, D.; Boutoux, G.; Brabetz, C.; Bradford, P.; Mancelli, D.; Neumayer, P.; Schiavi, A.; Trela, J.; Volpe, L.; et al. (Scientific Reports, 2019)
X-ray phase contrast imaging (XPCI) is more sensitive to density variations than X-ray absorption radiography, which is a crucial advantage when imaging weakly-absorbing, low-Z materials, or steep density gradients in matter under extreme conditions. Here, we describe the application of a polychromatic X-ray laser-plasma source (duration 0.5 ps, photon energy >1 keV) to the study of a laser-driven shock travelling in plastic material. The XPCI technique allows for a clear identification of the shock front as well as of small-scale features present during the interaction. Quantitative analysis of the compressed object is achieved using a density map reconstructed from the experimental data.
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Simulation of the multiphase configuration and phase transitions with quantum walks utilizing a step-dependent coin - Panahiyan, S.; Fritzsche, S. (Physical Review A, 2019)
Quantum walks are versatile simulators of topological phases and phase transitions as observed in condensed-matter physics. Here, we utilize a step-dependent coin in quantum walks and investigate what topological phases we can simulate with it, their topological invariants, bound states, and possibility of phase transitions. These quantum walks simulate nontrivial phases characterized by topological invariants (winding number) ±1, which are similar to the ones observed in topological insulators and polyacetylene. We confirm that the number of phases and their corresponding bound states increase step dependently. In contrast, the size of topological phase and distance between two bound states are decreasing functions of steps resulting into formation of multiple phases as quantum walks proceed (multiphase configuration). We show that, in the bound states, the winding number and group velocity are ill defined and the second moment of the probability density distribution in position space undergoes an abrupt change. Therefore, there are phase transitions taking place over the bound states and between two topological phases with different winding numbers.
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The magnetic toroidal sector as a broad-band electron–positron pair spectrometer I. lepton trajectories - Hagmann, S.; Hillenbrand, P.; Litvinov, Y.; Spillmann, U.; St{\"{o}}hlker, T. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2019)
We report an analysis of electron-optical properties of a toroidal magnetic sector spectrometer and examine parameters for its implementation in a relativistic heavy-ion storage ring like HESR. For studies of free-free pair production in heavy-ion atom collisions this spectrometer exhibits very high efficiencies for coincident e(+)- e(-) pair spectroscopy over a wide range of momenta of emitted lepton pairs. The high coincidence efficiency of the spectrometer is the key for stringent tests of theoretical predictions for the coincident positron- and electron emission characteristics and for the phase space correlation of lepton vector momenta in free-free pair production.
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23 mJ high-power fiber CPA system using electro-optically controlled divided-pulse amplification - Stark, H.; Buldt, J.; M{\"{u}}ller, M.; Klenke, A.; T{\"{u}}nnermann, A.; Limpert, J. (Optics Letters, 2019)
The pulse-energy scaling technique electro-optically controlled divided-pulse amplification is implemented in a high-power ultrafast fiber laser system based on coherent beam combination. A fiber-integrated front end and a multipass-cell-based back end allow for a small footprint and a modular implementation. Bursts of eight pulses are amplified parallel in up to 12 ytterbium-doped large-pitch fiber amplifiers. Subsequent spatiotemporal coherent combination of the 96 total amplified pulse replicas to a single pulse results in a pulse energy of 23 mJ at an average power of 674 W, compressible to a pulse duration of 235 fs. To the best of our knowledge, this is the highest pulse energy ever accomplished with a fiber chirped-pulse amplification (CPA) system.
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A study on the effects and visibility of low-order aberrations on laser beams with orbital angular momentum - Ohland, J. B.; Eisenbarth, U.; Roth, M.; Bagnoud, V. (Applied Physics B, 2019)
Laguerre–Gaussian-like laser beams have been proposed for driving experiments with high-intensity lasers. They carry orbital angular momentum and exhibit a ring-shaped intensity distribution in the far field which make them particularly attractive for various applications. We show experimentally and numerically that this donut-like shape is extremely sensitive to off-axis wavefront deformations. To support our claim, we generate a Laguerre–Gaussian-like laser beam and apply a selection of common low-order wavefront aberrations. We investigate the visibility of those wavefront deformations in the far field. Under use of established tolerance criteria, we determine the thresholds for the applied aberration and compare the findings with simulations for verification.
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Alternative approach to thermodynamic phase transitions - Hendi, S.; Panahiyan, S.; Panah, B.; Jamil, M. (Chinese Physics C, 2019)
One of the major open problems in theoretical physics is the lack of a consistent quantum gravity theory. Recent developments in our knowledge on thermodynamic phase transitions of black holes and their van der Waals-like behavior may provide an interesting quantum interpretation of classical gravity. Studying different methods of investigating phase transitions can extend our understanding of the nature of quantum gravity. In this paper, we present an alternative theoretical approach for finding thermodynamic phase transitions in the extended phase space. Unlike the standard methods based on the usual equation of state involving temperature, our approach uses a new quasi-equation constructed from the slope of temperature versus entropy. This approach addresses some of the shortcomings of the other methods and provides a simple and powerful way of studying the critical behavior of a thermodynamical system. Among the applications of this approach, we emphasize the analytical demonstration of possible phase transition points and the identification of the non-physical range of horizon radii for black holes.
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Channeling the dielectric breakdown of air by a sequence of laser-generated plasma filaments [Invited] - Polynkin, P.; Samsonova, Z.; Englesbe, A.; Lucero, A.; Elle, J.; Schmitt-Sody, A. (Journal of the Optical Society of America B, 2019)
We have investigated channeling the DC dielectric breakdown of a 20 cm air gap by a sequence of four concatenated plasma filaments, independently produced by four focused, 5-ps-long laser pulses. The polarity of the applied DC voltage, as well as the temporal delay between the four pulses, was varied from a few to 400 ns, in an attempt to find the optimum direction and speed of the stepping filament sequence. We have found that the filament sequence reliably channeled the breakdown and measurably reduced the breakdown threshold voltage, relative to that in the unguided breakdown. However, no meaningful dependence on either the polarity of the applied DC voltage or the stepping speed of the filament sequence was observed. Our results support the established scenario of channeling the DC air breakdown by laser filaments, which is primarily based on the creation of a reduced-density air channel bridging the discharge gap. The channeling mechanism associated with seeding the discharge leader by the filament plasma plays a negligible role.
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Characterization of laser-driven proton acceleration from water microdroplets - Becker, G.; Schwab, M.; L{\"{o}}tzsch, R.; Tietze, S.; Kl{\"{o}}pfel, D.; Rehwald, M.; Schlenvoigt, H.-P.; S{\"{a}vert, A. and Schramm, U. and Zepf, M. and Kaluza, M. (Scientific Reports, 2019)
We report on a proton acceleration experiment in which high-intensity laser pulses with a wavelength of 0.4 mm and with varying temporal intensity contrast have been used to irradiate water droplets of 20 mm diameter. Such droplets are a reliable and easy-to-implement type of target for proton acceleration experiments with the potential to be used at very high repetition rates. We have investigated the influence of the laser's angle of incidence by moving the droplet along the laser polarization axis. This position, which is coupled with the angle of incidence, has a crucial impact on the maximum proton energy. Central irradiation leads to an inefficient coupling of the laser energy into hot electrons, resulting in a low maximum proton energy. The introduction of a controlled pre-pulse produces an enhancement of hot electron generation in this geometry and therefore higher proton energies. However, two-dimensional particle-in-cell simulations support our experimental results confirming, that even slightly higher proton energies are achieved under grazing laser incidence when no additional pre-plasma is present. Illuminating a droplet under grazing incidence generates a stream of hot electrons that flows along the droplet's surface due to self-generated electric and magnetic fields and ultimately generates a strong electric field responsible for proton acceleration. The interaction conditions were monitored with the help of an ultra-short optical probe laser, with which the plasma expansion could be observed.
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Efficient Laser-Driven Proton Acceleration from a Cryogenic Solid Hydrogen Target - Polz, J.; Robinson, A. P. L.; Kalinin, A.; Becker, G. A.; Fraga, R.; Hellwing, M.; Hornung, M.; Keppler, S.; Kessler, A.; Kl{\"{o}}pfel, D.; Liebetrau, H.; Schorcht, F.; et al. (Scientific Reports, 2019)
We report on the successful implementation and characterization of a cryogenic solid hydrogen target in experiments on high-power laser-driven proton acceleration. When irradiating a solid hydrogen filament of 10 mm diameter with 10-Terawatt laser pulses of 2.5 J energy, protons with kinetic energies in excess of 20?MeV exhibiting non-thermal features in their spectrum were observed. The protons were emitted into a large solid angle reaching a total conversion efficiency of several percent. Two-dimensional particle-in-cell simulations confirm our results indicating that the spectral modulations are caused by collisionless shocks launched from the surface of the the high-density filament into a low-density corona surrounding the target. The use of solid hydrogen targets may significantly improve the prospects of laser-accelerated proton pulses for future applications.
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Generation of three-cycle multi-millijoule laser pulses at 318 W average power - Nagy, T.; H{\"{a}drich, S. and Simon, P. and Blumenstein, A. and Walther, N. and Klas, R. and Buldt, J. and Stark, H. and Breitkopf, S. and J{\'{o}}j{\'{a}}rt, P. and Seres, I. and V{\'{a}}rallyay, Z. and Eidam, T. and Limpert, J. (Optica, 2019)
The generation of three-cycle multi-millijoule pulses at 318 W power is reported by compressing pulses of a Yb-fiber chirped pulse amplifier in a 6 m long stretched flexible hollow fiber. This technique brings high-power lasers to the few-cycle regime.
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Laboratory setup for extreme ultraviolet coherence tomography driven by a high-harmonic source - Nathanael, J.; W{\"{u}}nsche, M.; Fuchs, S.; Weber, T.; Abel, J.; Reinhard, J.; Wiesner, F.; H{\"{u}}bner, U.; Skruszewicz, S.; Paulus, G.; R{\"{o}}del, C. (Review of Scientific Instruments, 2019)
We present a laboratory beamline dedicated to nanoscale subsurface imaging using extreme ultraviolet coherence tomography (XCT). In this setup, broad-bandwidth extreme ultraviolet (XUV) radiation is generated by a laser-driven high-harmonic source. The beamline is able to handle a spectral range of 30-130 eV and a beam divergence of 10 mrad (full width at half maximum). The XUV radiation is focused on the sample under investigation, and the broadband reflectivity is measured using an XUV spectrometer. For the given spectral window, the XCT beamline is particularly suited to investigate silicon-based nanostructured samples. Cross-sectional imaging of layered nanometer-scale samples can be routinely performed using the laboratory-scale XCT beamline. A depth resolution of 16 nm has been achieved using the spectral range of 36-98 eV which represents a 33% increase in resolution due to the broader spectral range compared to previous work.
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Laser-induced acceleration of Helium ions from unpolarized gas jets - Engin, I.; Chitgar, Z.; Deppert, O.; Lucchio, L.; Engels, R.; Fedorets, P.; Frydrych, S.; Gibbon, P.; Kleinschmidt, A.; Lehrach, A.; Maier, R.; Prasuhn, D.; et al. (Plasma Physics and Controlled Fusion, 2019)
In order to develop a laser-driven spin-polarized He-3-ion beam source available for nuclear-physics experiments as well as for the investigation of polarized nuclear fusion, several challenges have to be overcome. Apart from the provision of a properly polarized He-3 gas-jet target, one of the biggest milestones is the demonstration of the general feasibility of laser-induced ion acceleration out of gas-jet targets. Of particular importance is the knowledge about the main ion-emission angles as well as the achievable ion-energy spectra (dependent on the optimal set of laser and target parameters). We report on the results of such a feasibility study performed at PHELIX, GSI Darmstadt. Both He-3- and He-4-gas jets (n(gas) similar to 10(19) cm(-3)) were illuminated with high-intensity laser pulses, I-L similar to O(10(19) W cm(-2)). The main ion-emission angles could be identified (+/- 90 degrees with respect to the laser-propagation direction) and the ion-energy spectra for all ion species could be extracted: for the optimal laser and target parameters, the high-energy cut-offs for He-2+,He-1+ ions were 4.65 MeV (with a normalized energy uncertainty of Delta epsilon epsilon(-1) = 0.033) and 3.27 MeV (Delta epsilon epsilon(-1) = 0.055), respectively.
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Modeling terahertz emission from the target rear side during intense laser-solid interactions - Woldegeorgis, A.; Herzer, S.; Almassarani, M.; Marathapalli, S.; Gopal, A. (Physical Review E, 2019)
Relativistic laser-solid target interaction is a powerful source of terahertz radiation where broadband terahertz radiation is emitted from the front and rear surfaces of the target. Even though several experimental works have reported the generation of subpicosecond duration gigawatt peak power terahertz pulses from the target rear surface, the underlying physical process behind their origin is still an open question. Here we discuss a numerical model that can accurately reproduce several aspects of the experimental results. The model is based on the charged particle dynamics at the target rear surface and the evolution of the charge separation field. We identify the major contributors that are responsible for broadband terahertz emission from the rear surface of the target.
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Propagator from nonperturbative worldline dynamics - Franchino-Vi{\ {n}}as, S.; Gies, H. (Physical Review D, 2019)
We use the worldline representation for correlation functions together with numerical path integral methods to extract nonperturbative information about the propagator to all orders in the coupling in the quenched limit (small-Nf expansion). Specifically, we consider a simple two-scalar field theory with cubic interaction (S²QED) in four dimensions as a toy model for QED-like theories. Using a worldline regularization technique, we are able to analyze the divergence structure of all-order diagrams and to perform the renormalization of the model nonperturbatively. Our method gives us access to a wide range of couplings and coordinate distances. We compute the pole mass of the S²QED electron and observe sizable nonperturbative effects in the strong-coupling regime arising from the full photon dressing. We also find indications for the existence of a critical coupling where the photon dressing compensates the bare mass such that the electron mass vanishes. The short distance behavior remains unaffected by the photon dressing in accordance with the power-counting structure of the model.
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Single-pass non-destructive electronic detection of charged particles - Kiffer, M.; Ringleb, S.; Stallkamp, N.; Arndt, B.; Blinov, I.; Kumar, S.; Stahl, S.; St{\"{o}}hlker, T.; Vogel, M. (Review of Scientific Instruments, 2019)
We have devised an experimental method and apparatus for the simultaneous nondestructive determination of the absolute ion number, ion kinetic energy, and length of bunches of charged particles. We have built and operated a corresponding electronic detector that is based on induced charges and their subsequent low-noise amplification at cryogenic temperatures. We have performed measurements with bunches of low-energy highly charged ions from an electron-beam ion source that show the capability of the methods and their implementation. We discuss requirements for, and applications of, such detectors with a particular view on the obtainable information and their sensitivity.
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Spatiotemporal visualization of the terahertz emission during high-power laser-matter interaction - Gopal, A.; Woldegeorgis, A.; Herzer, S.; Almassarani, M. (Physical Review E, 2019)
Single-cycle pulses with multimillion volts per centimeter field strengths and spectra in the terahertz (THz) band have attracted great interest due to their ability to coherently manipulate molecular orientations and electron spins resonantly and nonresonantly. The tremendous progress made in the development of compact and powerful terahertz sources have identified intense laser-thin foil interaction as a potential candidate for high-power broadband terahertz radiation. They are micrometers in size and deliver radially polarized terahertz pulses with millijoule energy and gigawatt peak power. Although several works have been carried out to investigate the terahertz generation process, their origin and angular distribution are still debated. We present here an indisputable study on their spatiotemporal characteristics and elaborate the underlying physical processes via recording the three-dimensional beam profile along with transient dynamics. These results are substructured with the quantitative visualization of the charge particle spectra.
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Status of the Horizon 2020 EuPRAXIA conceptual design study - Weikum, M.; Akhter, T.; Alesini, D.; Alexandrova, A.; Anania, M.; Andreev, N.; Andriyash, I.; Aschikhin, A.; Assmann, R.; Audet, T.; Bacci, A.; Barna, I.; et al. (Journal of Physics: Conference Series, 2019)
The Horizon 2020 project EuPRAXIA (European Plasma Research Accelerator with eXcellence In Applications) is producing a conceptual design report for a highly compact and cost-effective European facility with multi-GeV electron beams accelerated using plasmas. EuPRAXIA will be set up as a distributed Open Innovation platform with two construction sites, one with a focus on beam-driven plasma acceleration (PWFA) and another site with a focus on laser-driven plasma acceleration (LWFA). User areas at both sites will provide access to free-electron laser pilot experiments, positron generation and acceleration, compact radiation sources, and test beams for high-energy physics detector development. Support centres in four different countries will complement the pan-European implementation of this infrastructure.
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Toward high contrast and high-resolution microscopic ghost imaging - Sun, Z.; Tuitje, F.; Spielmann, C. (Optics Express, 2019)
In this study, the influence of speckle size on contrast-to-noise ratio (CNR) and resolution is examined based on the object dimensions in the macroscopic and microscopic regimes. This research shows that for microscopic samples the conventional scaling laws are no longer effective and the CNR does not counter-propagate in the same manner as the resolution. To our knowledge, a deviation in CNR scaling on speckle size is observed for the first time in the field of microscopic ghost imaging. This result was verified using two different sample shapes. In addition, numerical analysis revealed that the noise of the photodiode is a limiting factor for the CNR. Based on these findings, the conditions for identifying the parameter set that maximizes the CNR and provides high resolution images was defined, which achieving high-quality microscopic ghost images.
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Formation of multi-spot focal arrays by square-shaped optical vortex lattices - Zhekova, M.; Maleshkov, G.; Stoyanov, L.; Stefanov, I.; Paulus, G.; Dreischuh, A. (Optics Communications, 2019)
In this work, we present numerical simulations and experimental evidence for the creation of controllable multi-spot focal arrays composed of bright beams with flat phase profiles. The input phase structures sent to spatial light modulators were square-shaped optical vortex (OV) lattices containing hundreds of vortices. In order to stabilize each of these lattices in space, all used OVs were singly charged and their topological charges varied alternatively across the structures. It is proven that the OV lattice node spacing can be used as a control parameter for reshaping the generated multi-spot focal arrays. Each peak of these arrays is shown to be able to additionally host a singular beam.
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g Factor of Lithiumlike Silicon: New Challenge to Bound-State QED - Glazov, D. A.; K{\"{o}}hler-Langes, F.; Volotka, A. V.; Blaum, K.; Hei{\"{s}}e, F.; Plunien, G.; Quint, W.; Rau, S.; Shabaev, V. M.; Sturm, S.; Werth, G. (Physical Review Letters, 2019)
The recently established agreement between experiment and theory for the g factors of lithiumlike silicon and calcium ions manifests the most stringent test of the many-electron bound-state quantum electrodynamics (QED) effects in the presence of a magnetic field. In this Letter, we present a significant simultaneous improvement of both theoretical gth=2.000 889 894 4 (34) and experimental gexp=2.000 889 888 45 (14) values of the g factor of lithiumlike silicon 28Si11+. The theoretical precision now is limited by the many-electron two-loop contributions of the bound-state QED. The experimental value is accurate enough to test these contributions on a few percent level.
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Modification of multipole transitions by twisted light - Schulz, S.-L.; Fritzsche, S.; M{\"{u}}ller, R. A.; Surzhykov, A. (Physical Review A, 2019)
A theoretical analysis is presented for the excitation of single many-electron atoms and ions by twisted (or vortex) light. Special emphasis is put on excitations that can proceed via several electric and magnetic multipole channels. We argue that the relative strength of these multipoles is very sensitive to the topological charge and kinematic parameters of the incident light and can be strongly modified with respect to the plane-wave case. Most remarkably, the modification of multipole transitions by twisted radiation can be described by means of a geometrical factor. This factor is independent of the shell structure of a particular target atom and just reflects the properties of the light beam as well as the position of an atom with respect to the vortex axis. An analytical expression for the geometrical factor is derived for Bessel photons and for a realistic experimental situation in which the position of an atom is not well determined. To illustrate the use of the geometrical factor for the analysis of (future) measurements, detailed calculations are presented for the presented for the 3s 3p 3P1 -> 3s 3p 1P1 excitation in neutral Mg.
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New test of modulated electron capture decay of hydrogen-like ¹⁴²Pm ions: Precision measurement of purely exponential decay - Ozturk, F.; Akkus, B.; Atanasov, D.; Beyer, H.; Bosch, F.; Boutin, D.; Brandau, C.; B{\"{u}}hler, P.; Cakirli, R.; Chen, R.; Chen, W.; Chen, X.; et al. (Physics Letters B, 2019)
An experiment addressing electron capture (EC) decay of hydrogen-like ¹⁴²Pm⁶⁰⁺ ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7) s⁻¹ for automatic analysis and 0.0141(7) s⁻¹ for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4).
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Picosecond contrast degradation by surface imperfections in chirped-pulse-amplification stretchers - Schanz, V. A.; Roth, M.; Bagnoud, V. (Journal of the Optical Society of America A, 2019)
In this paper, we propose a study of the picosecond temporal contrast degradation of ultrashort laser pulses by surface defects in pulse stretchers. In a chirped-pulse-amplification stretcher or compressor, dust and damages on the surface of an optical element lead to a spectral amplitude modulation. Furthermore, surface figure errors of optical elements happening where the pulse is spatially dispersed yield a modulation of the spectral phase. The influence of both amplitude and phase noise effects is numerically investigated using a hybrid ray-tracing method that enables treating separately the influence of noise sources, whether noise occurs in the near field or the far field. We show that the main issue in terms of picosecond contrast degradation is a combined effect of surface pattern distortion in the far field and phase–amplitude coupling caused by spatial frequency filters. Temporal domains can be defined, where the temporal contrast is dominated by different noise effects. The algorithm used in this paper is compared to the cross-correlation trace of a pulse. The conclusions emerging from the presented analysis are universally applicable to known grating stretcher geometries.
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Charge calibration of DRZ scintillation phosphor screens - Schwinkendorf, J.-P.; Bohlen, S.; Couperus Cabadağ, J.; Ding, H.; Irman, A.; Karsch, S.; K{\"{o}}hler, A.; Kr{\"{a}mer, J. and Kurz, T. and Kuschel, S. and Osterhoff, J. and Schaper, L. and Schinkel, D. and Schramm, U. and Zarini, O. and D'Arcy, R. (Journal of Instrumentation, 2019)
As a basic diagnostic tool, scintillation screens are employed in particle accelerators to detect charged particles. In extension to the recent revision on the calibration of scintillation screens commonly applied in the context of plasma acceleration [T. Kurz et al., Rev. Sci. Instrum. 89 (2018) 093303], herewe present the charge calibration of three DRZ screens (Std, Plus, High), which promise to offer similar spatial resolution to other screen types whilst reaching higher conversion efficiencies. The calibration was performed at the Electron Linac for beams with high Brilliance and low Emittance (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf, which delivers picosecond-long beams of up to 40 MeV energy. Compared to the most sensitive screen, Kodak BioMAX MS, of the aforementioned recent investigation by Kurz et al., the sample with highest yield in this campaign, DRZ High, revealed a 30% increase in light yield. The detection threshold with these screens was found to be below 10 pC/mm(2). For higher charge-densities (several nC/mm(2)) saturation effects were observed. In contrast to the recent reported work, the DRZ screens were more robust, demonstrating higher durability under the same high level of charge deposition.
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How to Observe the Vacuum Decay in Low-Energy Heavy-Ion Collisions - Maltsev, I. A.; Shabaev, V. M.; Popov, R. V.; Kozhedub, Y. S.; Plunien, G.; Ma, X.; St{\"{o}}hlker, T.; Tumakov, D. A. (Physical Review Letters, 2019)
In slow collisions of two bare nuclei with the total charge larger than the critical value Zcr≈173, the initially neutral vacuum can spontaneously decay into the charged vacuum and two positrons. The detection of the spontaneous emission of positrons would be direct evidence of this fundamental phenomenon. However, the spontaneously produced particles are indistinguishable from the dynamical background in the positron spectra. We show that the vacuum decay can nevertheless be observed via impact-sensitive measurements of pair-production probabilities. The possibility of such an observation is demonstrated using numerical calculations of pair production in low-energy collisions of heavy nuclei.
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Strong-Field Ionization with Few-Cycle Bessel Pulses: Interplay Between Orbital Angular Momentum and Carrier Envelope Phase - Paufler, W.; B{\"{o}}ning, B.; Fritzsche, S. (Quantum Collisions and Confinement of Atomic and Molecular Species, and Photons. Springer Proceedings in Physics, vol 23, 2019)
We study strong-field ionization of a hydrogenic target by few-cycle Bessel pulses. In order to investigate the interplay between the carrier envelope phase (CEP) and the orbital angular momentum of a few-cycle pulse (OAM), we apply a semiclassical two-step model. In particular, we here compute and discuss photoelectron momentum distributions (PEMD) for localized atomic targets. We show how these momentum distributions are affected by the CEP and TAM of the incident pulse. In particular, we find that the OAM affects the PEMD in a similar way as the CEP, depending on the initial position of our target.
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Tunable dual-comb from an all-polarization-maintaining single-cavity dual-color Yb:fiber laser - Fellinger, J.; Mayer, A. S.; Winkler, G.; Grosinger, W.; Truong, G.-W.; Droste, S.; Li, C.; Heyl, C. M.; Hartl, I.; Heckl, O. H. (Optics Express, 2019)
We demonstrate dual-comb generation from an all-polarization-maintaining dual-color ytterbium (Yb) fiber laser. Two pulse trains with center wavelengths at 1030 nm and 1060 nm respectively are generated within the same laser cavity with a repetition rate around 77 MHz. Dual-color operation is induced using a tunable mechanical spectral filter, which cuts the gain spectrum into two spectral regions that can be independently mode-locked. Spectral overlap of the two pulse trains is achieved outside the laser cavity by amplifying the 1030-nm pulses and broadening them in a nonlinear fiber. Spatially overlapping the two arms on a simple photodiode then generates a down-converted radio frequency comb. The difference in repetition rates between the two pulse trains and hence the line spacing of the down-converted comb can easily be tuned in this setup. This feature allows for a flexible adjustment of the tradeoff between non-aliasing bandwidth vs. measurement time in spectroscopy applications. Furthermore, we show that by fine-tuning the center-wavelengths of the two pulse trains, we are able to shift the down-converted frequency comb along the radio-frequency axis. The usability of this dual-comb setup is demonstrated by measuring the transmission of two different etalons while the laser is completely free-running.
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Wavelength-dependent nonsequential double ionization of magnesium by intense femtosecond laser pulses - Kang, H.; Chen, S.; Wang, Y.; Chu, W.; Yao, J.; Chen, J.; Liu, X.; Cheng, Y.; Xu, Z. (Physical Review A, 2019)
We report on a systematic investigation of wavelength scaling strong-field double ionization of Mg in intense laser fields. A significant decrease of nonsequential double ionization (NSDI) yield with increasing wavelength from 800-2000 nm is observed. Our data is well reproduced by a three-dimensional Monte Carlo simulation considering recollision impact excitation cross section. We demonstrate that the NSDI of Mg mainly occurs via the first ionic excited state Mg+*(3p(2)P(3/2)(,)(1/2)) pumped by returning electron impact process. The recollision impact direct ionization pathway plays a minor role here. The wavelength dependence of the NSDI ratio is due to the recollision energy-dependent excitation cross section as well as the electron wave packet diffusion effects, both sensitively depending on the wavelength. Our work represents a step towards strong-field double ionization experiments on Mg in the long wavelength limit and sheds light on the NSDI mechanism of alkaline-earth metal atoms.
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A fast alignment method for grating-based X-ray phase-contrast imaging systems - Schuster, M.; Ludwig, V.; Akstaller, B.; Seifert, M.; Wolf, A.; Michel, T.; Neumayer, P.; Funk, S.; Anton, G. (Journal of Instrumentation, 2019)
The alignment of a grating-based X-ray phase-contrast interferometer is an iterative process that requires numerous steps of changing the distances and angles between the gratings. For each alignment step an image is acquired to evaluate the detected intensity signature in order to optimize the observed moire pattern. Thus, a large number of images has to be taken for the alignment procedure. This is not feasible within reasonable time at X-ray sources like X-ray backlighters where the time between two X-ray shots is on the scale of hours. Here, we report on the development of a stable and transportable setup ready-to-use for grating-based X-ray phase-contrast imaging. A comprehensive set of reference images taken at a continuous beam serves as a look-up table which enables the grating alignment within very few alignment steps. Since this method features a fast, reliable and predictable alignment, it is also beneficial for grating-based X-ray phase-contrast imaging systems at common X-ray sources.
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Ab initio QED Treatment of the Two-Photon Annihilation of Positrons with Bound Electrons - Zaytsev, V. A.; Volotka, A. V.; Yu, D.; Fritzsche, S.; Ma, X.; Hu, H.; Shabaev, V. M. (Physical Review Letters, 2019)
The process of a positron{–}bound-electron annihilation with simultaneous emission of two photons is investigated theoretically. A fully relativistic formalism based on an ab initio QED description of the process is worked out. The developed approach is applied to evaluate the annihilation of a positron with K-shell electrons of a silver atom, for which a strong contradiction between theory and experiment was previously stated. The results obtained here resolve this longstanding disagreement and, moreover, demonstrate a sizable difference with approaches so far used for calculations of the positron{–}bound-electron annihilation process, namely, Lee’s and the impulse approximations.
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Boosting Quantum Vacuum Signatures by Coherent Harmonic Focusing - Karbstein, F.; Blinne, A.; Gies, H.; Zepf, M. (Physical Review Letters, 2019)
We show that coherent harmonic focusing provides an efficient mechanism to boost all-optical signatures of quantum vacuum nonlinearity in the collision of high-intensity laser fields, thereby offering a promising route to their first experimental detection. Assuming two laser pulses of given parameters at our disposal, we demonstrate a substantial increase of the number of signal photons measurable in experiments where one of the pulses undergoes coherent harmonic focusing before it collides with the fundamental-frequency pulse. Imposing a quantitative criterion to discern the signal photons from the background of the driving laser photons and accounting for the finite purity of polarization filtering, we find that signal photons arising from inelastic scattering processes constitute a promising signature. By contrast, quasielastic contributions which are conventionally assumed to form the most prospective signal remain background dominated. Our findings may result in a paradigm shift concerning which photonic signatures of quantum vacuum nonlinearity are accessible in experiment.
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Isotope shifts of the 1s²2s2p (J)–1s²2s²$ transition energies in Be-like thorium and uranium - Zubova, N. A.; Anisimova, I. S.; Kaygorodov, M. Y.; Kozhedub, Y. S.; Malyshev, A. V.; Shabaev, V. M.; Tupitsyn, I. I.; Plunien, G.; Brandau, C.; St{\"{o}}hlker, T. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2019)
Precise calculations of the isotope shifts in berylliumlike thorium and uranium ions are presented. The main contributions to the field and mass shifts are calculated within the framework of the Dirac–Coulomb–Breit Hamiltonian employing the configuration-interaction Dirac–Fock–Sturm method. These calculations include the relativistic, electron–electron correlation, and Breit-interaction effects. The QED, nuclear deformation, and nuclear polarization corrections are also evaluated.
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Laser photodetachment of radioactive ¹²⁸I⁻ - Rothe, S.; Sundberg, J.; Welander, J.; Chrysalidis, K.; Goodacre, T. D.; Fedosseev, V.; Fiotakis, S.; Forstner, O.; Heinke, R.; Johnston, K.; Kron, T.; K{\"{o}}ster, U.; et al. (Journal of Physics G: Nuclear and Particle Physics, 2019)
The first experimental investigation of the electron affinity (EA) of a radioactive isotope has been conducted at the CERN-ISOLDE radioactive ion beam facility. The EA of the radioactive iodine isotope ¹²⁸I (t 1/2 = 25 min) was determined to be 3.059 052(38) eV. The experiment was conducted using the newly developed Gothenburg ANion Detector for Affinity measurements by Laser PHotodetachment (GANDALPH) apparatus, connected to a CERN-ISOLDE experimental beamline. ¹²⁸I was produced in fission induced by 1.4 GeV protons striking a thorium/tantalum foil target and then extracted as singly charged negative ions at a beam energy of 20 keV. Laser photodetachment of the fast ion beam was performed in a collinear geometry inside the GANDALPH chamber. Neutral atoms produced in the photodetachment process were detected by allowing them to impinge on a glass surface, creating secondary electrons which were then detected using a channel electron multiplier. The photon energy of the laser was tuned across the threshold of the photodetachment process and the detachment threshold data were fitted to a Wigner law function in order to extract the EA. This first successful demonstration of photodetachment at an isotope separator on line facility opens up the opportunity for future studies of the fundamental properties of negatively charged radioactive isotopes such as the EA of astatine and polonium.
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Petawatt and exawatt class lasers worldwide - Danson, C.; Haefner, C.; Bromage, J.; Butcher, T.; Chanteloup, J.-C.; Chowdhury, E.; Galvanauskas, A.; Gizzi, L.; Hein, J.; Hillier, D. (High Power Laser Science and Engineering, 2019)
In the 2015 review paper Class Lasers Worldwide’ a comprehensive overview of the current status of high-power facilities of was presented. This was largely based on facility specifications, with some description of their uses, for instance in fundamental ultra-high-intensity interactions, secondary source generation, and inertial confinement fusion (ICF). With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification (CPA), which made these lasers possible, we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed. We are now in the era of multi-petawatt facilities coming online, with 100 PW lasers being proposed and even under construction. In addition to this there is a pull towards development of industrial and multi-disciplinary applications, which demands much higher repetition rates, delivering high-average powers with higher efficiencies and the use of alternative wavelengths: mid-IR facilities. So apart from a comprehensive update of the current global status, we want to look at what technologies are to be deployed to get to these new regimes, and some of the critical issues facing their development.
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Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles: with zero to relativistic speeds - Aumayr, F.; Ueda, K.; Sokell, E.; Schippers, S.; Sadeghpour, H.; Merkt, F.; Gallagher, T. F.; Dunning, F. B.; Scheier, P.; Echt, O.; Kirchner, T.; Fritzsche, S.; et al. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2019)
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
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Scattering of twisted light from a crystal - Peshkov, A. A.; Fritzsche, S.; Surzhykov, A. (Physica Scripta, 2019)
Recent years have seen significant progress in the generation and application of twisted beams carrying orbital angular momentum. Here we study the elastic scattering of twisted Bessel light from a crystal and compare our predictions with the results for incident plane-wave radiation. Based on form-factor approximation our numerical calculations of the differential scattering cross sections have been carried out for a crystal of lithium at x-ray energies. It is shown that the use of twisted light can lead to a measurable change in the scattering cross section for the nanocrystals approaching a few nm in size.
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X-ray photon scattering at a focused high-intensity laser pulse - Karbstein, F.; Mosman, E. A. (Physical Review D, 2019)
We study x-ray photon scattering in the head-on collision of an XFEL pulse and a focused high-intensity laser pulse, described as paraxial Laguerre-Gaussian beam of arbitrary mode composition. For adequately chosen relative orientations of the polarization vectors of the colliding laser fields, this gives rise to a vacuum birefringence effect manifesting itself in polarization flipped signal photons. Throughout this article the XFEL is assumed to be mildly focused to a waist larger than that of the high-intensity laser beam. As previously demonstrated for the special case of a fundamental paraxial Gaussian beam, this scenario is generically accompanied by a scattering phenomenon of x-ray energy signal photons outside the forward cone of the XFEL beam, potentially assisting the detection of the effect in experiment. Here, we study the fate of the x-ray scattering signal under exemplary deformations of the transverse focus profile of the high-intensity pump.
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A fresh computational approach to atomic structures, processes and cascades - Fritzsche, S. (Computer Physics Communications, 2019)
Electronic structure computations of atoms and ions have a long tradition in physics with applications in basic research, spectroscopy, life sciences and technology. Various theoretical methods (and codes) have therefore been developed to account for the many-particle structure of atoms, from simple semi-empirical estimates to accurate predictions of selected data, and up to highly advanced time-independent and time-dependent numerical techniques. {–} Here, I present a fresh concept and implementation of (relativistic) atomic structure theory that supports the computation of interaction amplitudes, properties as well as a large number of excitation and decay processes for open-shell atoms and ions across the whole periodic table. This implementation will facilitate also studies on atomic cascades, responses as well as the time-evolution of atoms and ions. It is based on Julia, a new programming language for scientific computing, and provides an easy-to-use but powerful platform to extent atomic theory towards new applications.
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Coherence control in high-order harmonic generation with Laguerre-Gaussian beams - Paufler, W.; B{\"{o}}ning, B.; Fritzsche, S. (Physical Review A, 2019)
We investigate phase matching for high-order harmonic generation with linearly polarized Laguerre-Gaussian (LG) beams with nonzero orbital angular momentum (OAM). We compare the conditions for efficient phase matching for LG beams with those of Gaussian beams. In particular, we show how the OAM of the incident beams affects the phase-matching conditions for the short and long trajectories that arise from the saddle-point approximation of the dipole moment. Thereby we illustrate that the coherence length for the short trajectories decreases for LG beams near the focus compared to Gaussian beams, whereas efficient phase matching can be achieved before and behind the focus. Furthermore, we demonstrate that the coherence length for the long trajectory behind the focus plane can be controlled by the OAM. This paper provides a route for the experiment in order to have good coherence control to enhance the conversion efficiency for high-order harmonic generation with beams carrying OAM.
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Evidence of Extreme Ultraviolet Superfluorescence in Xenon - Mercadier, L.; Benediktovitch, A.; Weninger, C.; Blessenohl, M.; Bernitt, S.; Bekker, H.; Dobrodey, S.; Sanchez-Gonzalez, A.; Erk, B.; Bomme, C.; Boll, R.; Yin, Z.; et al. (Physical Review Letters, 2019)
We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a free-electron laser pulse in a cell filled with Xe gas, the medium is quasi-instantaneously population inverted by 4d-shell ionization on the giant resonance followed by Auger decay. On the timescale of ∼10 ps to ∼100 ps (depending on parameters) a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission yield grows exponentially over four orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation.
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Flexible x-ray source with tunable polarization and orbital angular momentum from Hermite-Gaussian laser modes driven plasma channel wakefield - Lei, B.; Teter, T.; Wang, J. W.; Kharin, V. Yu.; Schroeder, C. B.; Zepf, M.; Rykovanov, S. G. (Physical Review Accelerators and Beams, 2019)
A plasma channel undulator/wiggler may be created through the plasma wakefield excited by the beating of several Hermite-Gaussian laser modes propagating in a parabolic plasma channel. Control over both the betatron and undulator forces is conveniently achieved by tuning the amplitude ratios, colors, and order numbers of the modes. A special structure of the undulator/wiggler field without the focusing force near the propagation axis is generated inside the plasma wakefield by matching the strengths of the fundamental and first-order Hermite-Gaussian modes. The electron beam only experiences forced undulator oscillations in such a field, which significantly improves the quality of the emitted radiation. Since the value of the undulator strength parameter could be in a wide range, less or larger than unity, it is capable of generating narrow bandwidth x-ray, as well as the synchrotronlike high-energy x/γ-ray, radiation by harmonics. Additionally, controlling the relative phases between the laser modes allows for polarization control of the plasma undulator. High-order harmonics produced from a circularly polarized plasma undulator clearly show the vortex nature and carry well-defined orbital angular momentum.
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Fluorescence polarization as a precise tool for understanding nonsequential many-photon ionization - Hofbrucker, J.; Volotka, A. V.; Fritzsche, S. (Physical Review A, 2019)
Nonsequential two-photon ionization of inner-shell np subshell of neutral atoms by circularly polarized light is investigated. Detection of subsequent fluorescence as a signature of the process is proposed and the dependence of fluorescence degree of polarization on incident photon beam energy is studied. It is generally expected that the degree of polarization remains approximately constant, except when the beam energy is tuned to an intermediate n′ resonance. However, strong unexpected change in the polarization degree is discovered for nonsequential two-photon ionization at specific incident beam energy due to a zero contribution of the otherwise dominant ionization channel. Polarization degree of the fluorescence depends less on the beam parameters, and its measurements at this specific beam energy, whose position is very sensitive to the details of the employed theory, are highly desirable for evaluation of theoretical calculations of nonlinear ionization at hitherto unreachable accuracy.
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High harmonic generation with Laguerre-Gaussian beams - Paufler, W.; B{\"{o}}ning, B.; Fritzsche, S. (Journal of Optics, 2019)
We summarize the development of high harmonic generation (HHG) with linearly polarized Laguerre–Gaussian (LG) beams and their superpositions to explain the non-perturbative aspects of HHG. Furthermore, we show that circularly polarized extreme ultraviolet vortices with well-defined orbital angular momentum (OAM) can be generated by HHG with bicircular LG beams. We introduce photon diagrams in order to explain how to calculate the OAM and the polarization of the generated harmonics by means of simultaneous conservation of spin angular momentum and OAM. Moreover, we show how the intensity ratio of the driving fields in HHG with bicircular LG beams further enhances the generation of circularly polarized twisted attosecond pulse trains.
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High-order implicit particle-in-cell method for plasma simulations at solid densities - Wu, D.; Yu, W.; Fritzsche, S.; He, X. T. (Physical Review E, 2019)
A high-order implicit multidimensional particle-in-cell (PIC) method is developed for simulating plasmas at solid densities. The space-time arrangement is based on Yee and a leapfrog algorithm for electromagnetic fields and particle advancement. The field solver algorithm completely eliminates numerical instabilities found in explicit PIC methods with relaxed time step and grid resolution. Moreover, this algorithm eliminates the numerical cooling found in the standard implicit PIC methods by using a pseudo-electric-field method. The particle pusher algorithm combines the standard Boris particle pusher with the Newton-Krylov iteration method. This algorithm increases the precision accuracy by several orders of magnitude when compared with the standard Boris particle pusher and also significantly decreases the iteration time when compared with the pure Newton-Krylov method. The code is tested with several benchmarks, including Weibel instability, and relativistic laser plasma interactions at both low and solid densities.
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Investigation of the temperature in dense carbon near the solid-liquid phase transition between 100 GPa and 200 GPa with spectrally resolved X-ray scattering - Helfrich, J.; Vorberger, J.; Frydrych, S.; Schaumann, G.; Ravasio, A.; Gauthier, M.; Fletcher, L.; Nagler, B.; Barbrel, B.; Bachmann, B.; Gamboa, E.; G{\"{o}}de, S.; et al. (High Energy Density Physics, 2019)
We present experiments investigating dense carbon at pressures between 100 GPa and 200 GPa and temperatures between 5,000 K and 15,000 K. High-pressure samples with different temperatures were created by laser-driven shock compression of graphite and varying the initial density from 1.53 g/cm³ to 2.21 g/cm³ and the drive laser intensity from 7.1 TW/cm² to 14.2 TW/cm². In order to deduce temperatures, spectrally resolved X-ray scattering was applied to determine ion-ion structure factors at a scattering vector of k = 4.12x10¹⁰ m⁻¹ which shows high sensitivity to temperature for the investigated sample conditions. After comparison to corresponding DFT-MD simulations, we were able to assign each structure factor a temperature. This information is indicative of the expected temperature range for the melting line of carbon at high pressures and can be compared to theoretical predictions.
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Laser based neutron spectroscopy - Kishon, I.; Kleinschmidt, A.; Schanz, V.; Tebartz, A.; Noam, O.; Fernandez, J.; Gautier, D.; Johnson, R.; Shimada, T.; Wurden, G.; Roth, M.; Pomerantz, I. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2019)
Great progress has been made in recent years in realizing compact, laser-based neutron generators. These devices, however, were inapplicable for conducting neutron absorption spectroscopy because of the electromagnetic noise produced by the interaction of a strong laser field with matter. To overcome this limitation, we developed a novel neutron time-of-flight detector, largely immune to electromagnetic noise. The detector is based on a plastic scintillator, only a few-millimeters in size, coupled with a silicon photo-multiplier by a long light-guiding fiber. Using this detector, we demonstrated for the first time laser-based fast neutron spectroscopy. This achievement paves the way to realizing compact neutron radiography systems for research, security, and commercial applications, and introduces new prospects for probing the temperature of matter under extreme conditions and for inertial confinement fusion diagnostics.
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Modeling of the 3D spatio-temporal thermal profile of joule-class Yb³⁺-based laser amplifiers - Tamer, I.; Keppler, S.; K{\"{o}}rner, J.; Hornung, M.; Hellwing, M.; Schorcht, F.; Hein, J.; Kaluza, M. (High Power Laser Science and Engineering, 2019)
Thermal profile modification of an active material in a laser amplifier via optical pumping results in a change in the material’s refractive index, and causes thermal expansion and stress, eventually leading to spatial phase aberrations, or even permanent material damage. For this purpose, knowledge of the 3D spatio-temporal thermal profile, which can currently only be retrieved via numerical simulations, is critical for joule-class laser amplifiers to reveal potentially dangerous thermal features within the pumped active materials. In this investigation, a detailed, spatio-temporal numerical simulation was constructed and tested for accuracy against surface thermal measurements of various end-pumped Yb³⁺-doped laser-active materials. The measurements and simulations show an excellent agreement and the model was successfully applied to a joule-class Yb³⁺-based amplifier currently operating in the POLARIS laser system at the Friedrich-Schiller-University and Helmholtz-Institute Jena in Germany.
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Particle-in-cell simulation of transport and energy deposition of intense proton beams in solid-state materials - Wu, D.; Yu, W.; Zhao, Y. T.; Hoffmann, D. H. H.; Fritzsche, S.; He, X. T. (Physical Review E, 2019)
A particle-in-cell (PIC) simulation code is used to investigate the transport and energy deposition of an intense proton beam in solid-state material. This code is able to simulate close particle interactions by using a Monte Carlo binary collision model. Such a model takes into account all related interactions between the incident protons and material particles, e.g., proton-nucleus, proton–bound-electron, and proton–free-electron collisions. This code also includes a Monte Carlo model for the collisional ionization and electron-ion recombination as well as the depression of the ionization potential by shielding of surrounding particles. Moreover, for intense proton beams, in order to include collective electromagnetic effects, significantly speed up the simulation, and simultaneously avoid numerical instabilities, an approach that combines the PIC method with a reduced model of high-density plasma based on Ohm's law is used. Simulation results indicate that the collective electromagnetic effects have a significant influence on the transport and energy deposition of proton beams. The Ohmic electric field would increase the stopping power and leads to a shortened range of proton beams in solid. The magnetic field would localize the energy deposition by collimating proton beams, which would otherwise be deflected by the collisions with nuclei.
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Properties of a cylindrical Penning trap with conical endcap openings - Kumar, S.; Quint, W.; Ringleb, S.; Safvan, C. P.; Stallkamp, N.; St{\"{o}}hlker, T.; Vogel, M. (Physica Scripta, 2019)
We describe the results of analytical calculations and numerical simulations of the confinement properties of a mechanically compensated cylindrical Penning trap which has conical endcap openings for large-solid-angle access for example with highly focused laser beams. While the analytical calculations show that under the common geometrical conditions the harmonicity of the confining fields near the centre of the trap does not change when a conical shape of the endcap electrodes is introduced, numerical simulations show significant changes when the opening angle of the cone exceeds a certain critical angle. We also show that these sharp features are due to the fringe-field effects above the critical angle, which are not described by the analytical calculations. These effects are also observed in a cylindrical Penning trap when the length of the endcap electrodes is reduced below a certain critical value.
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QED radiative corrections to the ²P₁/₂-²P₃/₂ fine structure in fluorinelike ions - Volotka, A. V.; Bilal, M.; Beerwerth, R.; Ma, X.; St{\"{o}}hlker, T.; Fritzsche, S. (Physical Review A, 2019)
calculations of QED radiative corrections to the 2P1/2 - 2P3/2 fine-structure transition energy are performed for selected F-like ions. These calculations are nonperturbative in αZ and include all first-order and many-electron second-order effects in α. When compared to approximate QED computations, a notable discrepancy is found especially for F-like uranium for which the predicted self-energy contributions even differ in sign. Moreover, all deviations between theory and experiment for the 2P1/2 - 2P3/2 fine-structure energies of F-like ions, reported recently by Li et al., Phys. Rev. A 98, 020502(R) (2018), are resolved if their highly accurate, non-QED fine-structure values are combined with the QED corrections ab initially evaluated here.
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Defects and mechanical properties in weakly damaged Si ion implanted GaAs - Creutzburg, S.; Schmidt, E.; Kutza, P.; Loetzsch, R.; Uschmann, I.; Undisz, A.; Rettenmayr, M.; Gala, F.; Zollo, G.; Boulle, A.; Debelle, A.; Wendler, E. (Physical Review B, 2019)
Damage formation is investigated in GaAs implanted with 1 MeV Si ions to ion fluences from 3 x 10(12) to 5 x 10(15) cm(-2) at room temperature. Under the conditions applied, amorphization of the implanted layers does not occur. The weakly damaged layers are studied by applying different experimental techniques including Rutherford backscattering spectrometry in channeling configuration, x-ray diffraction, in situ curvature measurement, optical subgap spectroscopy, and transmission electron microscopy. The results are evaluated and quantitatively connected with each other. Damage formation is described as a function of the ion fluence using a common defect evolution model. Point defects and defect clusters have to be taken into account in the ion fluence range of main interest up to 2 x 10(15) cm(-2). Point defects contribute by a factor of about 8 more to both perpendicular strain and in-plane stress than defect clusters. When the concentration of point defects or the induced strain reaches a critical value, defect clusters form, which ensures that no further increase of perpendicular strain occurs. This reveals a clear driving force for cluster formation. The microstructure of the defect clusters cannot be determined from the results. As3Ga2 interstitial clusters are supposed. A remarkable decrease of the shear modulus of the implanted layers below the value of pristine GaAs by approximate to -35% is observed. Surprisingly, the change of shear modulus already sets in at a very low damage level of a few percent.
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Differential cross sections for ionization of atomic hydrogen by antiprotons - Bondarev, A.; Kozhedub, Y.; Tupitsyn, I.; Shabaev, V.; Plunien, G.; St{\"{o}}hlker, T. (Hyperfine Interactions, 2019)
We consider ionization of atomic hydrogen by antiproton impact. Doubly differential cross sections for ionization calculated within a recently developed semiclassical approach by Bondarev et al. (Phys. Rev. A 95, 052709, 2017) are presented. Comparison of the obtained results with other theoretical predictions is given.
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Formation of relativistic electromagnetic solitons in over-dense plasmas - Wu, D.; Yu, W.; Fritzsche, S.; Zheng, C. Y.; He, X. T. (Physics of Plasmas, 2019)
We report the formation of electromagnetic solitons in over-dense plasmas in the relativistic transparency regime. By using one-dimensional and two-dimensional particle-in-cell simulations, the formation and basic properties of these long-lived relativistic electromagnetic solitons are studied. The predicted mechanism of soliton formation is different from the existing investigations. The latter ones are found to exist in the wake of the high-intensity laser pulse during the interaction with a low density plasma, and such solitons are made of low-frequency, spatially localized electromagnetic fields. While for the former ones, frequency of solitons formed in the relativistic transparency regime is comparable to incident laser frequency. Moreover, a threshold of plasma density under which stable solitons can be formed is analyzed. These newly predicted solitons are expected to be observed in the present-day laser-plasma experiments.
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g Factor of Boronlike Argon ⁴⁰Ar¹³⁺ - Arapoglou, I.; Egl, A.; H{\"{o}}cker, M.; Sailer, T.; Tu, B.; Weigel, A.; Wolf, R.; Cakir, H.; Yerokhin, V. A.; Oreshkina, N. S.; Agababaev, V. A.; Volotka, A. V.; et al. (Physical Review Letters, 2019)
We have measured the ground-state g factor of boronlike argon 40Ar13+ with a fractional uncertainty of 1.4×10−9 with a single ion in the newly developed Alphatrap double Penning-trap setup. The value of g=0.663 648 455 32(93) obtained here is in agreement with our theoretical prediction of 0.663 648 12(58). The latter is obtained accounting for quantum electrodynamics, electron correlation, and nuclear effects within the state-of-the-art theoretical methods. Our experimental result distinguishes between existing predictions that are in disagreement, and lays the foundations for an independent determination of the fine-structure constant.
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Gamma Factory at CERN - Novel Research Tools Made of Light - Placzek, W.; Abramov, A.; Alden, S.; Alemany Fernandez, R.; Antsiferov, P.; Apyan, A.; Bartosik, H.; Bessonov, E.; Biancacci, N.; Bieron, J.; Bogacz, A.; Bosco, A.; et al. (Acta Physica Polonica B, 2019)
We discuss the possibility of creating novel research tools by producing and storing highly relativistic beams of highly ionised atoms in the CERN accelerator complex, and by exciting their atomic degrees of freedom with lasers to produce high-energy photon beams. Intensity of such photon beams would be by several orders of magnitude higher than offered by the presently operating light sources, in the particularly interesting gamma-ray energy domain of 0.1-400 MeV. In this energy range, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. New research opportunities in a wide domain of fundamental and applied physics can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams.
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Ground-state hyperfine splitting of B-like ions in the high-Z region - Glazov, D. A.; Volotka, A. V.; Andreev, O. V.; Kosheleva, V. P.; Fritzsche, S.; Shabaev, V. M.; Plunien, G.; St{\"{o}}hlker, T. (Physical Review A, 2019)
The hyperfine splitting of the ground state of selected B-like ions within the range of nuclear charge numbers Z=49–83 is investigated in detail. The rigorous QED approach together with the large-scale configuration-interaction Dirac-Fock-Sturm method are employed for the evaluation of the interelectronic-interaction contributions of first and higher orders in 1/Z. The screened QED corrections are evaluated to all orders in αZ by using an effective potential. The influence of nuclear magnetization distribution is taken into account within the single-particle nuclear model.
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High-precision calculations of the 1s²2s2p ¹P₁->1s²2s² ¹S₀ spin-allowed E1 transition in C iii - Bilal, M.; Volotka, A. V.; Beerwerth, R.; Rothhardt, J.; Hilbert, V.; Fritzsche, S. (Physical Review A, 2019)
Large-scale relativistic calculations are performed for the transition energy and line strength of the 1s22s2p 1P1− 1s22s2 1S0 transition in Be-like carbon. Based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) approach, different correlation models are developed to account for all major electron-electron correlation contributions. These correlation models are tested with various sets of the initial and the final state wave functions. The uncertainty of the predicted line strength due to missing correlation effects is estimated from the differences between the results obtained with those models. The finite nuclear mass effect is accurately calculated taking into account the energy, wave functions as well as operator contributions. As a result, a reliable theoretical benchmark of the E1 line strength is provided to support high precision lifetime measurement of the 1s22s2p 1P1 state in Be-like carbon.
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Momentum dependence of quantum critical Dirac systems - Dabelow, L.; Gies, H.; Knorr, B. (Physical Review D, 2019)
We analyze fermionic criticality in relativistic 2 + 1 dimensional fermion systems using the functional renormalization group (FRG), concentrating on the Gross-Neveu (chiral Ising) and the Thirring model. While a variety of methods, including the FRG, appear to reach quantitative consensus for the critical regime of the Gross-Neveu model, the situation seems more diverse for the Thirring model with different methods yielding vastly different results. We present a first exploratory FRG study of such fermion systems including momentum-dependent couplings using pseudo-spectral methods. Our results corroborate the stability of results in Gross-Neveu-type universality classes, but indicate that momentum dependencies become more important in Thirring-type models for small flavor numbers. For larger flavor numbers, we confirm the existence of a non-Gaussian fixed point and thus a physical continuum limit. In the large-N limit, we obtain an analytic solution for the momentum dependence of the fixed-point vertex.
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Relative amplitude noise transfer function of an Yb3+-doped fiber amplifier chain - Gierschke, P.; Jauregui, C.; Gottschall, T.; Limpert, J. (Optics Express, 2019)
In this work we measure the frequency dependent transfer function of the amplitude noise for both the seed and pump power in an Yb3+-doped fiber amplifier chain. In particular, the relative intensity noise transfer function of this amplifier chain in the frequency range of 10 Hz – 100 kHz has been investigated. It is shown that the pump power noise of the pre-amplifier stages is transformed into seed power noise for the next amplification stage. Crucially, the seed power noise in the frequency range of interest is strongly damped by the main-amplifier. This, however, does not happen for the pump power noise. Thus, the noise of the pump of the last amplifier stage is the factor with the strongest impact on the overall noise level of the system. Finally, useful guidelines to minimize the output amplitude noise of an Yb3+-doped fiber amplifier chain are given.
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Scheme dependence of asymptotically free solutions - Gies, H.; Sondenheimer, R.; Ugolotti, A.; Zambelli, L. (The European Physical Journal C, 2019)
Recent studies have provided evidence for the existence of new asymptotically free trajectories in non-Abelian particle models without asymptotic symmetry in the high-energy limit. We extend these results to a general SU(N-L) x SU(N-c) Higgs-Yukawa model that includes the non-Abelian sector of the standard model, finding further confirmation for such scenarios for a wide class of regularizations that account for threshold behavior persisting to highest energies. We construct these asymptotically free trajectories within conventional (MS) over bar schemes and systematic weak coupling expansions. The existence of these solutions is argued to be a scheme-independent phenomenon, as demonstrated for mass-dependent schemes based on general momentum-space infrared regularizations. A change of scheme induces a map of the theory's coupling space onto itself, which in the present case also translates into a reparametrization of the space of asymptotically free solutions.
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All-Loop Result for the Strong Magnetic Field Limit of the Heisenberg-Euler Effective Lagrangian - Karbstein, F. (Physical Review Letters, 2019)
We provide an explicit expression for the strong magnetic field limit of the Heisenberg-Euler effective Lagrangian for both scalar and spinor quantum electrodynamics. To this end, we show that the strong magnetic field behavior is fully determined by one-particle reducible contributions discovered only recently. The latter can efficiently be constructed in an essentially algebraic procedure from lower-order one-particle reducible diagrams. Remarkably, the leading strong magnetic field behavior of the all-loop Heisenberg-Euler effective Lagrangian only requires input from the one-loop Lagrangian. Our result revises previous findings based exclusively on one-particle irreducible contributions. In addition, we briefly discuss the strong electric field limit and comment on external field QED in the large N limit.
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Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in ²¹⁷,²¹⁸,²¹⁹At revealed by in-source laser spectroscopy - Barzakh, A. E.; Cubiss, J. G.; Andreyev, A. N.; Seliverstov, M. D.; Andel, B.; Antalic, S.; Ascher, P.; Atanasov, D.; Beck, D.; Bieron, J.; Blaum, K.; Borgmann, Ch.; et al. (Physical Review C, 2019)
Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in 217, 218, 219At have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope 218At has been found to be larger than the average of its even-N neighbors, 217, 219At. The discrepancy between the additivity-rule prediction and experimental data for the magnetic moment of 218At also supports the possible presence of octupole collectivity in the considered nuclei.
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Nondipole strong-field approximation for spatially structured laser fields - B{\"{o}}ning, B.; Paufler, W.; Fritzsche, S. (Physical Review A, 2019)
The strong-field approximation (SFA) is widely used to theoretically describe the ionization of atoms and molecules in intense laser fields. We here propose an extension of the SFA to incorporate nondipole contributions in the interaction between the photoelectron and the driving laser field. To this end, we derive Volkov-type continuum wave functions of an electron propagating in a laser field of arbitrary spatial dependence. Based on previous work by L. Rosenberg and F. Zhou [Phys. Rev. A 47, 2146 (1993)], we show how to construct such Volkov-type solutions to the Schr{\"{o}}dinger equation for an electron in a vector potential that can be written as an integral superposition of plane waves. These solutions are therefore not restricted to plane waves but are also appropriate to deal with more complex laser fields like twisted Bessel or Laguerre-Gaussian beams, where the magnetic field plays an important role. As an example, we compute photoelectron spectra in the above-threshold ionization of atoms with a single-mode plane-wave laser field of midinfrared wavelength. Especially, we demonstrate how peak offsets in the p_z direction can be extracted that result from the nondipole nature of the interaction. Here, we find good agreement with previous theoretical and experimental studies for circular polarization and discuss differences for linear polarization.
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Optimizing Laser Pulses for Narrow-Band Inverse Compton Sources in the High-Intensity Regime - Seipt, D.; Kharin, V.; Rykovanov, S. (Physical Review Letters, 2019)
Scattering of ultraintense short laser pulses off relativistic electrons allows one to generate a large number of X- or gamma-ray photons with the expense of the spectral width{–}-temporal pulsing of the laser inevitable leads to considerable spectral broadening. In this Letter, we describe a simple method to generate optimized laser pulses that compensate the nonlinear spectrum broadening and can be thought of as a superposition of two oppositely linearly chirped pulses delayed with respect to each other. We develop a simple analytical model that allows us to predict the optimal parameters of such a two-pulse{–}-the delay, amount of chirp, and relative phase{–}-for generation of a narrow-band $γ$-ray spectrum. Our predictions are confirmed by numerical optimization and simulations including three-dimensional effects.
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Perturbative methods for assisted nonperturbative pair production - Torgrimsson, G. (Physical Review D, 2019)
In the dynamically assisted Schwinger mechanism, the pair production probability is significantly enhanced by including a weak, rapidly varying field in addition to a strong, slowly varying field. In a previous paper we showed that several features of dynamical assistance can be understood by a perturbative treatment of the weak field. Here we show how to calculate the prefactors of the higher-orders terms, which is important because the dominant contribution can come from higher orders. We give a new and independent derivation of the momentum spectrum using the worldline formalism, and extend our WKB approach to calculate the amplitude to higher orders. We show that these methods are also applicable to doubly assisted pair production.
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Radiative electron capture as a tunable source of highly linearly polarized x rays - Vockert, M.; Weber, G.; Br{\"{a}uning, H. and Surzhykov, A. and Brandau, C. and Fritzsche, S. and Geyer, S. and Hagmann, S. and Hess, S. and Kozhuharov, C. and M{\"{a}rtin, R. and Petridis, N. and Hess, R. and Trotsenko, S. and Litvinov, Yu. A. and Glorius, J. and Gumberidze, A. and Steck, M. and Litvinov, S. and Gassner, T. and Hillenbrand, P.-M. and Lestinsky, M. and Nolden, F. and Sanjari, M. S. and Popp, U. and Trageser, C. and Winters, D. F. A. and Spillmann, U. and Krings, T. and St{\"{o}}hlker, T. (Physical Review A, 2019)
The radiative electron capture (REC) into the K shell of bare Xe ions colliding with a hydrogen gas target has been investigated. In this study, the degree of linear polarization of the K-REC radiation was measured and compared with rigorous relativistic calculations as well as with the previous results recorded for U92+. Owing to the improved detector technology, a significant gain in precision of the present polarization measurement is achieved compared to the previously published results. The obtained data confirms that for medium-Z ions such as Xe, the REC process is a source of highly polarized x rays which can easily be tuned with respect to the degree of linear polarization and the photon energy. We argue, in particular, that for relatively low energies the photons emitted under large angles are almost fully linear polarized.
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Relativistic Interaction of Long-Wavelength Ultrashort Laser Pulses with Nanowires - Samsonova, Z.; H{\"{o}}fer, S.; Kaymak, V.; Ali{{s}}auskas, S.; Shumakova, V.; Pug{{z}}lys, A.; Baltuska, A.; Siefke, T.; Kroker, S.; Pukhov, A.; Rosmej, O.; Uschmann, I.; et al. (Physical Review X, 2019)
We report on experimental results in a new regime of relativistic light-matter interaction employing midinfrared (3.9-mu m wavelength) high-intensity femtosecond laser pulses. In the laser-generated plasma, electrons reach relativistic energies already for rather low intensities due to the fortunate lambda(2) scaling of the kinetic energy with the laser wavelength. The lower intensity efficiently suppresses optical field ionization and creation of the preplasma at the rising edge of the laser pulse, enabling an enhanced efficient vacuum heating of the plasma. The lower critical plasma density for long-wavelength radiation can be surmounted by using nanowires instead of flat targets. Numerical simulations, which are in a good agreement with experimental results, suggest that approximate to 80% of the incident laser energy has been absorbed resulting in a long-living, key-temperature, high-charge-state plasma with a density more than 3 orders of magnitude above the critical value. Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate.
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Single nanowire defined emission properties of ZnO nanowire arrays - Hollinger, R.; Gupta, D.; Zapf, M.; R{\"{o}}der, R.; Kartashov, D.; Ronning, C.; Spielmann, C. (Journal of Physics D: Applied Physics, 2019)
We report on stimulated emission from vertically aligned, vapor transport grown, ZnO nanowire arrays, and pumped by three-photon absorption in intense near-infrared femtosecond laser pulses. In respect to single nanowires, arrays have the advantage of a higher light absorption and emission rate. The intensity and bandwidth of the emitted ultraviolet radiation as a function of the pump intensity is compared for nanowire arrays with different wire lengths, diameters, and spacing. The measured lasing thresholds for all arrays can be well described by the geometry of individual nanowire lasers, showing that coupling effects between the individual emitters in the arrays are negligible, even for the smallest 100 nm diameter wires with an average distance of 200 nm.
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Spin states in multiphoton pair production for circularly polarized light - Kohlf{\"{u}}rst, C. (Physical Review D, 2019)
Scalar and fermionic particle pair production in rotating electric fields is investigated in the nonperturbative multiphoton regime. Angular momentum distribution functions in above-threshold pair production processes are calculated numerically within quantum kinetic theory and discussed on the basis of a photon absorption model. The particle spectra can be understood if the spin states of the particle-antiparticle pair are taken into account.
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Strong Light-Field Driven Nanolasers - Hollinger, R.; Malevich, P.; Shumakova, V.; Ali{{s}}auskas, S.; Zapf, M.; R{\"{o}}der, R.; Pug{{z}}lys, A.; Baltuska, A.; Ronning, C.; Spielmann, C.; Kartashov, D. (Nano Letters, 2019)
Einstein established the quantum theory of radiation and paved the way for modern laser physics including single-photon absorption by charge carriers and finally pumping an active gain medium into population inversion. This can be easily understood in the particle picture of light. Using intense, ultrashort pulse lasers, multiphoton pumping of an active medium has been realized. In this nonlinear interaction regime, excitation and population inversion depend not only on the photon energy but also on the intensity of the incident pumping light, which can be still described solely by the particle picture of light. We demonstrate here that lowering significantly the pump photon energy further still enables population inversion and lasing in semiconductor nanowires. The extremely high electric field of the pump bends the bands and enables tunneling of electrons from the valence to the conduction band. In this regime, the light acts by the classical Coulomb force and population inversion is entirely due to the wave nature of electrons, thus the excitation becomes independent of the frequency but solely depends on the incident intensity of the pumping light.
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Target fabrication for laser-ion acceleration research at the Technological Laboratory of the LMU Munich - Szerypo, J.; Ma, W.; Bothmann, G.; Hahner, D.; Haug, M.; Hilz, P.; Kreuzer, C.; Lange, R.; Seuferling, S.; Speicher, M.; Stehr, F.; Stork, S.; et al. (Matter and Radiation at Extremes, 2019)
The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching. Our main focus here is on the production of free-standing, thin foil targets, such as diamond-likecarbon foils, carbon nanotube foams (CNFs), plastic, and gold foils. The presented methods comprise cathodic arc deposition for DLC targets, chemical vapor deposition for CNFs, a droplet and spin-coating process for plastic foil production, as well as physical vapor deposition that has been optimized to provide ultrathin gold foils and tailored sacrifice layers. This paper reviews our current capabilities, which are a result of a close collaboration between target production processes and experiment, using high-power chirped pulse amplification laser systems over the past eight years.
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The hyperfine puzzle of strong-field bound-state QED - N{\"{o}}rtersh{\"{a}user, W. and Ullmann, J. and Skripnikov, L. V. and Andelkovic, Z. and Brandau, C. and Dax, A. and Geithner, W. and Geppert, C. and Gorges, C. and Hammen, M. and Hannen, V. and Kaufmann, S. and K{\"{o}}nig, K. and Kraus, F. and Kresse, B. and Litvinov, Y. A. and Lochmann, M. and Maass, B. and Meisner, J. and Murb{\"{o}}ck, T. and Privalov, A. F. and Sanchez, R. and Scheibe, B. and Schmidt, M. and Schmidt, S. and Shabaev, V. M. and Steck, M. and St{\"{o}}hlker, T. and Thompson, R. C. and Trageser, C. and Vogel, M. and Vollbrecht, J. and Volotka, A. V. and Weinheimer, C. (Hyperfine Interactions, 2019)
The hyperfine splitting in heavy highly charged ions provide the means to test QED in extremely strong magnetic fields. In order to provide a meaningful test, the splitting has to be measured in H-like and Li-like ions to remove uncertainties from nuclear structure. This has been achieved at the experimental storage ring ESR but a discrepancy to the theoretical prediction of more than 7s was observed. We report on these measurements as well as on NMR measurements that were performed to solve this issue.
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Thermally versus dynamically assisted Schwinger pair production - Torgrimsson, G. (Physical Review D, 2019)
We study electron-positron pair production by the combination of a strong, constant electric field and a thermal background. We show that this process is similar to dynamically assisted Schwinger pair production, where the strong field is instead assisted by another coherent field, which is weaker but faster. We treat the interaction with the photons from the thermal background perturbatively, while the interaction with the electric field is nonperturbative (i.e., a Furry picture expansion in α). At O(α2) we have ordinary perturbative Breit-Wheeler pair production assisted nonperturbatively by the electric field. Already at this order we recover the same exponential part of the probability as previous studies, which did not expand in α. This means that we do not have to consider higher orders, so our approach allows us to calculate the preexponential part of the probability, which has not been obtained before in this regime. Although the prefactor is in general subdominant compared to the exponential part, in this case it can be important because it scales as α2≪1 and is therefore much smaller than the prefactor at O(α0) (pure Schwinger pair production). We show that, because of the exponential enhancement, O(α2) still gives the dominant contribution for temperatures above a certain threshold, but, because of the small prefactor, the threshold is higher than what the exponential alone would suggest.
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BRST-invariant RG flows - Asnafi, S.; Gies, H.; Zambelli, L. (Physical Review D, 2019)
A mass parameter for the gauge bosons in gauge-fixed four-dimensional Yang-Mills theory can be accommodated in a local and manifestly Becchi-Rouet-Stora-Tyutin invariant action. The construction is based on the Faddeev-Popov method involving a nonlinear gauge-fixing and a background Nakanishi-Lautrup field. When applied to momentum-dependent masslike deformations, this formalism leads to a full regularization of the theory which explicitly preserves Becchi-Rouet-Stora-Tyutin symmetry. We deduce a functional renormalization group equation for the one-particle-irreducible effective action, which has a one-loop form. The master equation is compatible with it-i.e., Becchi-Rouet-Stora-Tyutin symmetry is preserved along the flow-and it has a standard regulator-independent Zinn-Justin form. As a first application, we compute the leading-order gluon wave-function renormalization.
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Comment on “Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime” - Witte, B. B. L.; R{\"{o}}pke, G.; Neumayer, P.; French, M.; Sperling, P.; Recoules, V.; Glenzer, S. H.; Redmer, R. (Physical Review E, 2019)
Dharma-wardana et al. [M. W. C. Dharma-wardana et al., Phys. Rev. E 96, 053206 (2017)] recently calculated dynamic electrical conductivities for warm dense matter as well as for nonequilibrium two-temperature states termed “ultrafast matter” (UFM) [M. W. C. Dharma-wardana, Phys. Rev. E 93, 063205 (2016)]. In this Comment we present two evident reasons why these UFM calculations are neither suited to calculate dynamic conductivities nor x-ray Thomson scattering spectra in isochorically heated warm dense aluminum. First, the ion-ion structure factor, a major input into the conductivity and scattering spectra calculations, deviates strongly from that of isochorically heated aluminum. Second, the dynamic conductivity does not show a non-Drude behavior which is an essential prerequisite for a correct description of the absorption behavior in aluminum. Additionally, we clarify misinterpretations by Dharma-wardana et al. concerning the conductivity measurements of Gathers [G. R. Gathers, Int. J. Thermophys. 4, 209 (1983)].
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Electrostatic capacitance-type acceleration of ions with an intense few-cycle laser pulse - Shen, X.; Qiao, B.; Zhang, H.; Xie, Y.; Kar, S.; Borghesi, M.; Zepf, M.; Zhou, C.; Zhu, S.; He, X. (Applied Physics Letters, 2019)
We use large scale, three-dimensional particle-in-cell simulations to demonstrate that a high-quality energetic ion beam can be stably generated by irradiation of a multi-species nanofoil target with an intense few-cycle laser pulse. In this scheme named capacitance-type acceleration,the light ions of the nanofoil are accelerated by a uniform capacitor-like electrostatic field induced by the laser-blown-out electrons that act like the cathode of a capacitor, while the heavy ions left behind serve as the anode. This scheme overcomes the inherent obstacles existing in the other acceleration mechanisms, such as uncontrollability of target normal sheath acceleration and instability of radiation pressure acceleration. Theoretical studies and three-dimensional particle-in-cell simulations show that this acceleration scheme is much more stable and efficient than the previous ones, by which 100 MeV monoenergetic proton beams (energy spread <10%) can be obtained with a laser energy less than 10 J, and the giga electron volt ones with about 100 J.
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Excitation of the ²²⁹Th nucleus via a two-photon electronic transition - M{\"{u}}ller, R.; Volotka, A.; Surzhykov, A. (Physical Review A, 2019)
We investigate the process of nuclear excitation via a two-photon electron transition (NETP) for the case of the doubly charged thorium. The theory of the NETP process was originally devised for heavy-helium-like ions. In this work, we study this process in the nuclear clock isotope 229Th in the 2+ charge state. For this purpose we employ a combination of configuration interaction and many-body perturbation theory to calculate the probability of NETP in resonance approximation. The experimental scenario we propose for the excitation of the low-lying isomeric state in 229Th is a circular process starting with a two-step pumping stage followed by NETP. The ideal intermediate steps in this process depends on the supposed energy ℏωN of the nuclear isomeric state. For each of these energies, the best initial state for NETP is calculated. Special focus is put on the most recent experimental results for ℏωN.
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Frequency-comb-based laser system producing stable optical beat pulses with picosecond durations suitable for high-precision multi-cycle terahertz-wave generation and rapid detection - Schimpf, D.; Olgun, H.; Kalaydzhyan, A.; Hua, Y.; Matlis, N.; K{\"{a}rtner, F. X. (Optics Express, 2019)
We generate temporally modulated optical pulses with a beat frequency of 255 GHz, a duration of 360 ps, and a repetition rate of 2 MHz. The temporal envelope, beat frequency, and repetition rate are computer-programmable. A frequency comb serves as a phase and frequency reference for the locking of two laser lines. The system enables beat frequencies that are adjustable in steps of the frequency comb's repetition rate and exhibit Hz-level precision and accuracy. We expect the optical beat pulses to be well suited for versatile multi-cycle terahertz-wave generation with controllable carrier-envelope phase. We demonstrate that the inherent synchronization of the frequency comb's ultra-short pulse train and the synthesized optical beat (or later the multi-cycle terahertz) pulses enables rapid and phase-sensitive sampling of such pulses.
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High dynamic range, large temporal domain laser pulse measurement - Schanz, V. A.; Brabetz, C.; Posor, D. J.; Reemts, D.; Roth, M.; Bagnoud, V. (Applied Physics B, 2019)
Temporal pulse profile characterization is necessary to ensure and quantify the quality of short pulse laser systems. Yet it remains challenging to measure the temporal behavior of a pulse in all of its comprehensiveness. In this manuscript we present results which encourage to perform more ambitious pulse characterizations with optimized scanning cross-correlators. Several temporal laser pulse profile measurements in multiple nanosecond time scale with high dynamic range are shown. The measurements were taken by our in-house third-order cross-correlator EICHEL (Schanz et al. in Opt Express 25:9252, 2017), which is able to resolve the intensity dynamics down to the level of amplified spontaneous emission. With this device we show for the first time the onset of the plateau of the amplified spontaneous emission in the laser profile and investigate the origin of several side-pulses created early in the laser system.
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Lifetimes and g -factors of the HFS states in H-like and Li-like bismuth - Hannen, V.; Vollbrecht, J.; Andelkovic, Z.; Brandau, C.; Dax, A.; Geithner, W.; Geppert, C.; Gorges, C.; Hammen, M.; Kaufmann, S.; K{\"{o}}nig, K.; Litvinov, Y.; et al. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2019)
The LIBELLE experiment performed at the experimental storage ring at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, has successfully determined the ground state hyperfine (HFS) splittings in hydrogen-like (Bi-209(82+)) and lithium-like (Bi-209(80+)) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. Besides the transition wavelengths the time-resolved detection of fluorescence photons following the excitation of the ions by a pulsed laser system also allows the extraction of lifetimes of the upper HFS levels and g-factors of the bound 1s and 2s electrons for both charge states. While the lifetime of the upper HFS state in Bi-209(82+) has already been measured in earlier experiments, an experimental value for lifetime of this state in Bi-209(80+) is reported for the first time in this work.
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Monochromatic 2D Kα Emission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism - Sawada, H.; Sentoku, Y.; Yabuuchi, T.; Zastrau, U.; F{\"{o}}rster, E.; Beg, F. N.; Chen, H.; Kemp, A. J.; McLean, H. S.; Patel, P. K.; Ping, Y. (Physical Review Letters, 2019)
The rapid heating of a thin titanium foil by a high intensity, subpicosecond laser is studied by using a 2D narrow-band x-ray imaging and x-ray spectroscopy. A novel monochromatic imaging diagnostic tuned to 4.51 keV Ti K alpha was used to successfully visualize a significantly ionized area (< Z > > 17 +/- 1) of the solid density plasma to be within a similar to 35 mu m diameter spot in the transverse direction and 2 mu m in depth. The measurements and a 2D collisional particle-in-cell simulation reveal that, in the fast isochoric heating of solid foil by an intense laser light, such a high ionization state in solid titanium is achieved by thermal diffusion from the hot preplasma in a few picoseconds after the pulse ends. The shift of K alpha and formation of a missing K alpha cannot be explained with the present atomic physics model. The measured K alpha image is reproduced only when a phenomenological model for the K alpha shift with a threshold ionization of < Z > = 17 is included. This work reveals how the ionization state and electron temperature of the isochorically heated nonequilibrium plasma are independently increased.
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Photon-Photon Scattering at the High-Intensity Frontier: Paraxial Beams - Blinne, A.; Gies, H.; Karbstein, F.; Kohlf{\"{u}}rst, C.; Zepf, M. (Journal of Physics: Conference Series, 2019)
Our goal is to study optical signatures of quantum vacuum nonlinearities in strong macroscopic electromagnetic fields provided by high-intensity laser beams. The vacuum emission scheme is perfectly suited for this task as it naturally distinguishes between incident laser beams, described as classical electromagnetic fields driving the effect, and emitted signal photons encoding the signature of quantum vacuum nonlinearity. Using the Heisenberg-Euler effective action, our approach allows for a reliable study of photonic signatures of QED vacuum nonlinearity in the parameter regimes accessible by all-optical high-intensity laser experiments. To this end, we employ an efficient, flexible numerical algorithm, which allows for a detailed study of the signal photons emerging in the collision of focused paraxial high-intensity laser pulses. Due to the high accuracy of our numerical solutions we predict the total number of signal photons, but also have full access to the signal photons’ characteristics, including their spectrum, propagation directions and polarizations. We discuss setups offering an excellent background-to-noise ratio, thus providing an important step towards the experimental verification of quantum vacuum nonlinearities.
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The Vacuum Emission Picture Beyond Paraxial Approximation - Blinne, A.; Gies, H.; Karbstein, F.; Kohlf{\"{u}}rst, C.; Zepf, M. (Journal of Physics: Conference Series, 2019)
Optical signatures of the effective nonlinear couplings among electromagnetic fields in the quantum vacuum can be conveniently described in terms of stimulated photon emission processes induced by strong classical, space-time dependent electromagnetic fields. Recent studies have adopted this approach to study collisions of Gaussian laser pulses in paraxial approximation. The present study extends these investigations beyond the paraxial approximation by using an efficient numerical solver for the classical input fields. This new numerical code allows for a consistent theoretical description of optical signatures of QED vacuum nonlinearities in generic electromagnetic fields governed by Maxwell’s equations in the vacuum, such as manifestly non-paraxial laser pulses. Our code is based on a locally constant field approximation of the Heisenberg-Euler effective Lagrangian. As this approximation is applicable for essentially all optical high-intensity laser experiments, our code is capable of calculating signal photon emission amplitudes in completely generic input field configurations, limited only by numerical cost.
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Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region - Butler, T. P.; Gerz, D.; Hofer, C.; Xu, J.; Gaida, C.; Heuermann, T.; Gebhardt, M.; Vamos, L.; Schweinberger, W.; Gessner, J. A.; Siefke, T.; Heusinger, M.; et al. (Optics Letters, 2019)
We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6{–}18 µm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse difference-frequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 µm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-µm pulses in GaSe.
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Approaching the Gamow Window with Stored Ions: Direct Measurement of ¹²⁴Xe(p,γ) in the ESR Storage Ring - Glorius, J.; Langer, C.; Slavkovsk{\'{a}}, Z.; Bott, L.; Brandau, C.; Br{\"{u}}ckner, B.; Blaum, K.; Chen, X.; Dababneh, S.; Davinson, T.; Erbacher, P.; Fiebiger, S.; et al. (Physical Review Letters, 2019)
We report the first measurement of low-energy proton-capture cross sections of 124Xe in a heavy-ion storage ring. 124Xe^54+ ions of five different beam energies between 5.5 and 8 AMeV were stored to collide with a windowless hydrogen target. The 125Cs reaction products were directly detected. The interaction energies are located on the high energy tail of the Gamow window for hot, explosive scenarios such as supernovae and x-ray binaries. The results serve as an important test of predicted astrophysical reaction rates in this mass range. Good agreement in the prediction of the astrophysically important proton width at low energy is found, with only a 30% difference between measurement and theory. Larger deviations are found above the neutron emission threshold, where also neutron and γ widths significantly impact the cross sections. The newly established experimental method is a very powerful tool to investigate nuclear reactions on rare ion beams at low center-of-mass energies.
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Electron- and proton-impact excitation of heliumlike uranium in relativistic collisions - Gumberidze, A.; Thorn, D. B.; Surzhykov, A.; Fontes, C. J.; Najjari, B.; Voitkiv, A.; Fritzsche, S.; Bana{ś}, D.; Beyer, H. F.; Chen, W.; Grisenti, R. E.; Hagmann, S.; et al. (Physical Review A, 2019)
We have studied the K-shell excitation of He-like uranium (U90+) in relativistic collisions with hydrogen and argon atoms. Performing measurements with different targets, as well as with different collision energies, enabled us to explore the proton- (nucleus-) impact excitation as well as the electron-impact excitation process for the heaviest He-like ion. The large fine-structure splitting in uranium allowed us to partially resolve excitation into different L-shell levels. State-of-the-art relativistic calculations which include excitation mechanisms due to the interaction with both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the electron-impact excitation process.
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Evidence for Crystalline Structure in Dynamically-Compressed Polyethylene up to 200 GPa - Hartley, N. J.; Brown, S.; Cowan, T. E.; Cunningham, E.; D{\"{o}}ppner, T.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Garcia, A. L.; Gericke, D. O.; et al. (Scientific Reports, 2019)
We investigated the high-pressure behavior of polyethylene (CH2) by probing dynamically-compressed samples with X-ray diffraction. At pressures up to 200 GPa, comparable to those present inside icy giant planets (Uranus, Neptune), shock-compressed polyethylene retains a polymer crystal structure, from which we infer the presence of significant covalent bonding. The A2/m structure which we observe has previously been seen at significantly lower pressures, and the equation of state measured agrees with our findings. This result appears to contrast with recent data from shock-compressed polystyrene (CH) at higher temperatures, which demonstrated demixing and recrystallization into a diamond lattice, implying the breaking of the original chemical bonds. As such chemical processes have significant implications for the structure and energy transfer within ice giants, our results highlight the need for a deeper understanding of the chemistry of high pressure hydrocarbons, and the importance of better constraining planetary temperature profiles.
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Multi-parameter optimization of a loose focusing high flux high-harmonic beamline - Kovacs, K.; Major, B.; Balogh, E.; Koros, C.; Rudawaski, S. P.; Heyl, C. M.; Johnsson, P.; Arnold, C. L.; Hullier, A. L.; Tosa, V.; Varju, K. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2019)
We perform a multi-dimensional parameter scan in the generation of high-order harmonics, with the main purpose to find the macroscopic conditions that optimize the harmonic yield in a specific spectral domain, around 40 eV for this particular case. The scanned parameters are the laser pulse energy, gas pressure, interaction cell position relative to focus and the cell length, while the fixed parameters are chosen to model a loose focusing configuration which is used in many existing laboratories. We performed the simulations with a 3D non-adiabatic model complemented by a detailed analysis of the phase matching mechanisms involved in an efficient harmonic generation. Based on the results we identify a range of parameter combinations that lead to a high yield in the specified spectral domain The method and results presented here can be the framework for the design and construction of high flux high-order harmonic generation beamlines.
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Plasma environment effects on K lines of astrophysical interest - I. Atomic structure, radiative rates, and Auger widths of oxygen ions - Deprince, J.; Bautista, M. A.; Fritzsche, S.; Garc{\'{i}}a, J. A.; Kallman, T. R.; Mendoza, C.; Palmeri, P.; Quinet, P. (A{ &}A, 2019)
Aims. In the context of black-hole accretion disks, the main goal of the present study is to estimate the plasma environment effects on the atomic structure and radiative parameters associated with the K-vacancy states in ions of the oxygen isonuclear sequence. Methods. We used a time-averaged Debye–H{\"{u}}ckel potential for both the electron–nucleus and the electron–electron interactions implemented in the fully relativistic multiconfiguration Dirac–Fock (MCDF) method. Results. Modified ionization potentials, K thresholds, Auger widths, and radiative transition wavelengths and rates are reported for O I–O VII in plasma environments with electron temperature and density ranges 105−107 K and 1018−1022 cm−3.
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X-ray phase-contrast imaging for laser-induced shock waves - Antonelli, L.; Barbato, F.; Mancelli, D.; Trela, J.; Zeraouli, G.; Boutoux, G.; Neumayer, P.; Atzeni, S.; Schiavi, A.; Volpe, L.; Bagnoud, V.; Brabetz, C.; et al. (Europhysics Letters, 2019)
X-ray phase-contrast imaging (XPCI) is a versatile technique with applications in many fields, including fundamental physics, biology and medicine. Where X-ray absorption radiography requires high density ratios for effective imaging, the image contrast for XPCI is a function of the density gradient. In this letter, we apply XPCI to the study of laser-driven shock waves. Our experiment was conducted at the Petawatt High-Energy Laser for Heavy Ion EXperiments (PHELIX) at GSI. Two laser beams were used: one to launch a shock wave and the other to generate an X-ray source for phase-contrast imaging. Our results suggest that this technique is suitable for the study of warm dense matter (WDM), inertial confinement fusion (ICF) and laboratory astrophysics.
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3.42 µm lasing in heavily-erbium-doped fluoride fibers - Maes, F.; Stihler, C.; Pleau, L.-P.; Fortin, V.; Limpert, J.; Bernier, M.; Vall{\'{e}}e, R. (Optics Express, 2019)
In this paper, we investigate laser emission at 3.4μm in heavily-erbium-doped fluoride fibers using dual-wavelength pumping. To this extent, a monolithic 7 mol% erbium-doped fluoride fiber laser bounded by intracore fiber Bragg gratings at 3.42 μm is used to demonstrate a record efficiency of 38.6 % with respect to the 1976 nm pump. Through numerical modeling, we show that similar laser performances at 3.4 μm can be expected in fluoride fibers with erbium concentrations ranging between 1 – 7 mol%, although power scaling should rely on lightly-doped fibers to mitigate the heat load. Moreover, this work studies transverse mode-beating of the 1976 nm core pump and its role in the generation of a periodic luminescent grating and in the trapping of excitation in the metastable energy levels of the erbium system. Finally, we also report on the bistability of the 3.42 μm output power of the 7 mol% erbium-doped fluoride fiber laser.
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A high resolution extreme ultraviolet spectrometer system optimized for harmonic spectroscopy and XUV beam analysis - W{\"{u}}nsche, M.; Fuchs, S.; Weber, T.; Nathanael, J.; Abel, J.; Reinhard, J.; Wiesner, F.; H{\"{u}}bner, U.; Skruszewicz, S.; Paulus, G.; R{\"{o}}del, C. (Review of Scientific Instruments, 2019)
We present a modular extreme ultraviolet (XUV) spectrometer system optimized for a broad spectral range of 12-41 nm (30-99 eV) with a high spectral resolution of lambda/Delta lambda greater than or similar to 784 +/- 89. The spectrometer system has several operation modes for (1) XUV beam inspection, (2) angular spectral analysis, and (3) imaging spectroscopy. These options allow for a versatile use in high harmonic spectroscopy and XUV beam analysis. The high performance of the spectrometer is demonstrated using a novel cross-sectional imaging method called XUV coherence tomography.
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Asymptotic freedom in Z2-Yukawa-QCD models - Gies, H.; Sondenheimer, R.; Ugolotti, A.; Zambelli, L. (The European Physical Journal C, 2019)
Z2-Yukawa-QCD models are a minimalistic model class with a Yukawa and a QCD-like gauge sector that exhibits a regime with asymptotic freedom in all its marginal couplings in standard perturbation theory. We discover the existence of further asymptotically free trajectories for these models by exploiting generalized boundary conditions. We construct such trajectories as quasi-fixed points for the Higgs potential within different approximation schemes. We substantiate our findings first in an effective-field-theory approach, and obtain a comprehensive picture using the functional renormalization group. We infer the existence of scaling solutions also by means of a weak-Yukawa-coupling expansion in the ultraviolet. In the same regime, we discuss the stability of the quasi-fixed point solutions for large field amplitudes. We provide further evidence for such asymptotically free theories by numerical studies using pseudo-spectral and shooting methods.
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Crystal orientation-dependent polarization state of high-order harmonics - You, Y. S.; Lu, J.; Cunningham, E. F.; R{\"{o}}del, C.; Ghimire, S. (Optics Letters, 2019)
We analyze the crystal orientation-dependent polarization state of extreme ultraviolet high-order harmonics from bulk magnesium oxide crystals subjected to intense linearly polarized laser fields. We find that only along high-symmetry directions do high-order harmonics follow the polarization direction of the laser field. In general, there are strong deviations that depend on harmonic order, strength of the laser field, and crystal orientation. We use a real-space electron trajectory picture to understand the origin of polarization deviations. These results have implications in all-optical probing of electronic band structure in momentum space and valence charge distributions in real space, and in producing attosecond pulses with time-dependent polarization in compact setups.
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