Referierte Publikationen


L. Bocklage, J. Gollwitzer, C. Strohm, C. Adolff, K. Schlage, I. Sergeev, O. Leupold, H.-C. Wille, G. Meier, and R. Röhlsberger
Coherent control of collective nuclear quantum states via transient magnons
Science Advances, 7 :eabc3991 (January 2021)
Ultrafast and precise control of quantum systems at x-ray energies involves photons with oscillation periods below 1 as. Coherent dynamic control of quantum systems at these energies is one of the major challenges in hard x-ray quantum optics. Here, we demonstrate that the phase of a quantum system embedded in a solid can be coherently controlled via a quasi-particle with subattosecond accuracy. In particular, we tune the quantum phase of a collectively excited nuclear state via transient magnons with a precision of 1 zs and a timing stability below 50 ys. These small temporal shifts are monitored interferometrically via quantum beats between different hyperfine-split levels.The experiment demonstrates zeptosecond interferometry and shows that transient quasi-particles enable accurate control of quantum systems embedded in condensed matter environments.
A. T. Schmitt, Y. Joly, K. S. Schulze, B. Marx-Glowna, I. Uschmann, B. Grabiger, H. Bernhardt, R. Lötzsch, A. Juhin, J. Debray, H.-C. Wille, H. Yavaş, G.G. Paulus, and R. Röhlsberger
Disentangling x-ray dichroism and birefringence via high-purity polarimetry
Optica, 8 :56 (January 2021)
High-brilliance synchrotron radiation sources have opened new avenues for x-ray polarization analysis that go far beyond conventional polarimetry in the optical domain. With linear x-ray polarizers in a crossed setting, polarization extinction ratios down to 10⁻¹⁰ can be achieved. This renders the method sensitive to probe the tiniest optical anisotropies that would occur, for example, in strong-field quantum electrodynamics due to vacuum birefringence and dichroism. Here we show that high-purity polarimetry can be employed to reveal electronic anisotropies in condensed matter systems with utmost sensitivity and spectral resolution. Taking CuO and La₂CuO₄ as benchmark systems, we present a full characterization of the polarization changes across the Cu K-absorption edge and their separation into dichroic and birefringent contributions. At diffraction-limited synchrotron radiation sources and x-ray lasers, where polarization extinction ratios of 10⁻¹² can be achieved, our method has the potential to assess birefringence and dichroism of the quantum vacuum in extreme electromagnetic fields.
L. Wollenweber, T. R. Preston, A. Descamps, V. Cerantola, A. Comley, J. H. Eggert, L. B. Fletcher, G. Geloni, D. O. Gericke, S. H. Glenzer, S. Goede, J. Hastings, O. S. Humphries, A. Jenei, O. Karnbach, Z. Konopkova, R. Lötzsch, B. Marx-Glowna, E. E. McBride, D. McGonegle, G. Monaco, B. K. Ofori-Okai, C. A. J. Palmer, C. Plückthun, R. Redmer, C. Strohm, I. Thorpe, T. Tschentscher, I. Uschmann, J. S. Wark, T. G. White, K. Appel, G. Gregori, and U. Zastrau
High-resolution inelastic x-ray scattering at the high energy density scientific instrument at the Free-Electron Laser
Rev. Sci. Instrum., 92 :013101 (January 2021)
We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. An energy resolution of 44 meV is demonstrated for the experimental setup, close to the theoretically achievable minimum resolution. The analyzer crystals and detector are mounted on a curved-rail system, allowing quick and reliable changes in scattering angle without breaking vacuum. The entire setup is designed for operation at 10 Hz, the same repetition rate as the high-power lasers available at the instrument and the fundamental repetition rate of the European XFEL. Among other measurements, it is envisioned that this setup will allow studies of the dynamics of highly transient laser generated states of matter.
R. Hollinger, P. Herrmann, V. Korolev, M. Zapf, V. Shumakova, R. Roeder, I. Uschmann, A. Pugžlys, A. Baltuska, M. Zürch, C. Ronning, C. Spielmann, and D. Kartashov
Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO
Nanomaterials, 11 :4 (January 2021)
The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this work we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3-4 mu m. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.
S. Strnat, V. A. Yerokhin, A. V. Volotka, G. Weber, S. Fritzsche, R. A. Müller, and A. Surzhykov
Polarization studies on Rayleigh scattering of hard x rays by closed-shell atoms
Phys. Rev. A, 103 :012801 (January 2021)
We present a theoretical study on the elastic Rayleigh scattering of x-ray photons by closed-shell atoms. Special attention is paid to the transfer of linear polarization from the incident to the outgoing photons. To study this process, we apply the density-matrix formalism combined with the relativistic perturbation theory. This formalism enables us to find general relations between the Stokes parameters of the incident and scattered photons. By using these expressions, we revisit the recent proposal to use Rayleigh scattering for the analysis of the polarization purity of synchrotron radiation. We show that this analysis can be performed without any need for the theoretically calculated scattering amplitudes, if the linear polarization of the scattered light is measured simultaneously at the azimuthal angles 0 degrees and 45 degrees with respect to the plane of the synchrotron. To illustrate our approach, we present detailed calculations for scattering of 145 keV photons by lead atoms.
S. Panahiyan, and S. Fritzsche
Toward simulation of topological phenomena with one-, two-, and three-dimensional quantum walks
Phys. Rev. A, 103 :012201 (January 2021)
We study the simulation of the topological phases in three subsequent dimensions with quantum walks. We focus mainly on the completion of a table for the protocols of the quantum walk that could simulate different families of the topological phases in one, two, and three dimensions. We also highlight the possible boundary states that can be observed for each protocol in different dimensions and extract the conditions for their emergences. To further enrich the simulation of the topological phenomena, we include step-dependent coins in the evolution operators of the quantum walks. This leads to step dependence of the simulated topological phenomena and their properties which introduces dynamicity as a feature of simulated topological phases and boundary states. This dynamicity provides the step number of the quantum walk as a means to control and engineer the numbers of topological phases and boundary states, their numbers, types, and even occurrences.
K. S. Schulze, R. Lötzsch, R. Rüffer, I. Uschmann, R. Röhlsberger, and G.G. Paulus
X-ray dichroism in polyimide caused by non-resonant scattering
J. Synchrotron Radiat., 28 :176 (January 2021)
Dichroism is one of the most important optical effects in both the visible and the X-ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.


E. Shestaev, S. Haedrich, N. Walther, T. Eidam, A. Klenke, I. Seres, Z. Bengery, P. Jójárt, Z. Várallyay, A. Borzsonyi, and J. Limpert
Carrier-envelope offset stable, coherently combined ytterbium-doped fiber CPA delivering 1 kW of average power
Opt. Lett., 45 :6350 (December 2020)
We present a carrier-envelope offset (CEO) stable ytterbium-doped fiber chirped-pulse amplification system employing the technology of coherent beam combining and delivering more than 1 kW of average power at a pulse repetition rate of 80 MHz. The CEO stability of the system is 220 mrad rms, characterized out-of-loop with an f-to-2f interferometer in a frequency offset range of 10 Hz to 20 MHz. The high-power amplification system boosts the average power of the CEO stable oscillator by five orders of magnitude while increasing the phase noise by only 100 mrad. No evidence of CEO noise deterioration due to coherent beam combining is found. Low-frequency CEO fluctuations at the chirped-pulse amplifier are suppressed by a slow loop feedback. To the best of our knowledge, this is the first demonstration of a coherently combined laser system delivering an outstanding average power and high CEO stability at the same time.
I. Tamer, M. Hornung, L. Lukas, M. Hellwing, S. Keppler, R. Van Hull, J. Hein, M. Zepf, and M.C. Kaluza
Characterization and application of nonlinear plastic materials for post-CPA pulse compression
Opt. Lett., 45 :6575 (December 2020)
We demonstrate the three-fold post-chirped-pulse-amplification (post-CPA) pulse compression of a high peak power laser pulse using ally) diglycol carbonate (CR39), which was selected as the optimal material for near-field self-phase modulation out of a set of various nonlinear plastic materials, each characterized with respect to its nonlinear refractive index and optical transmission. The investigated materials could be applied for further pulse compression at high peak powers, as well as for gain narrowing compensation within millijoule-class amplifiers. The post-CPA pulse compression technique was tested directly after the first CPA stage within the POLARIS laser system, with the compact setup containing a single 1 mm thick plastic sample and a chirped mirror pair, which enabled a substantial shortening of the compressed pulse duration and, hence, a significant increase in the laser peak power without any additional modifications to the existing CPA chain.
R. W. Assmann, M. K. Weikum, T. Akhter, D. Alesini, A. S. Alexandrova, M. P. Anania, N. E. Andreev, I. Andriyash, M. Artioli, A. Aschikhin, T. Audet, A. Bacci, I. F. Barna, S. Bartocci, A. Bayramian, A. Beaton, A. Beck, M. Bellaveglia, A. Beluze, A. Bernhard, A. Biagioni, S. Bielawski, F. G. Bisesto, A. Bonatto, L. Boulton, F. Brandi, R. Brinkmann, F. Briquez, F. Brottier, E. Bründermann, M. Büscher, B. Buonomo, M. H. Bussmann, G. Bussolino, P. Campana, S. Cantarella, K. Cassou, A. Chance, M. Chen, E. Chiadroni, A. Cianchi, F. Cioeta, J. A. Clarke, J. M. Cole, G. Costa, M.-E. Couprie, J. Cowley, M. Croia, B. Cros, P. A. Crump, R. D’Arcy, G. Dattoli, A. Del Dotto, N. Delerue, M. Del Franco, P. Delinikolas, S. De Nicola, J. M. Dias, D. Di Giovenale, M. Diomede, E. Di Pasquale, G. Di Pirro, G. Di Raddo, U. Dorda, A. C. Erlandson, K. Ertel, A. Esposito, F. Falcoz, A. Falone, R. Fedele, A. Ferran Pousa, M. Ferrario, F. Filippi, J. Fils, G. Fiore, R. Fiorito, R. A. Fonseca, G. Franzini, M. Galimberti, A. Gallo, T. C. Galvin, A. Ghaith, A. Ghigo, D. Giove, A. Giribono, L. A. Gizzi, F. J. Grüner, A. F. Habib, C. Haefner, T. Heinemann, A. Helm, B. Hidding, B. J. Holzer, S. M. Hooker, T. Hosokai, M. Hübner, M. Ibison, S. Incremona, A. Irman, F. Iungo, F. J. Jafarinia, O. Jakobsson, D. A. Jaroszynski, S. Jaster-Merz, C. Joshi, M. Kaluza, M. Kando, O. S. Karger, S. Karsch, E. Khazanov, D. Khikhlukha, M. Kirchen, G. Kirwan, C. Kitégi, A. Knetsch, D. Kocon, P. Koester, O. S. Kononenko, G. Korn, I. Kostyukov, K. O. Kruchinin, L. Labate, C. Le Blanc, C. Lechner, P. Lee, W. Leemans, A. Lehrach, X. Li, Y. Li, V. Libov, A. Lifschitz, C. A. Lindstrøm, V. Litvinenko, W. Lu, O. Lundh, A. R. Maier, V. Malka, G. G. Manahan, S. P. D. Mangles, A. Marcelli, B. Marchetti, O. Marcouillé, A. Marocchino, F. Marteau, A. Martinez de la Ossa, J. L. Martins, P. D. Mason, F. Massimo, F. Mathieu, G. Maynard, Z. Mazzotta, S. Mironov, A. Y. Molodozhentsev, S. Morante, A. Mosnier, A. Mostacci, A.-S. Müller, C. D. Murphy, Z. Najmudin, P. A. P. Nghiem, F. Nguyen, P. Niknejadi, A. Nutter, J. Osterhoff, D. Oumbarek Espinos, J.-L. Paillard, D. N. Papadopoulos, B. Patrizi, R. Pattathil, L. Pellegrino, A. Petralia, V. Petrillo, L. Piersanti, M. A. Pocsai, K. Poder, R. Pompili, L. Pribyl, D. Pugacheva, B. A. Reagan, J. Resta-Lopez, R. Ricci, S. Romeo, M. Rossetti Conti, A. R. Rossi, R. Rossmanith, U. Rotundo, E. Roussel, L. Sabbatini, P. Santangelo, G. Sarri, L. Schaper, P. Scherkl, U. Schramm, C. B. Schroeder, J. Scifo, L. Serafini, G. Sharma, Z. M. Sheng, V. Shpakov, C. W. Siders, L. O. Silva, T. Silva, C. Simon, C. Simon-Boisson, U. Sinha, E. Sistrunk, A. Specka, T. M. Spinka, A. Stecchi, A. Stella, F. Stellato, M. J. V. Streeter, A. Sutherland, E. N. Svystun, D. Symes, C. Szwaj, G. E. Tauscher, D. Terzani, G. Toci, P. Tomassini, R. Torres, D. Ullmann, C. Vaccarezza, M. Valléau, M. Vannini, A. Vannozzi, S. Vescovi, J. M. Vieira, F. Villa, C.-G. Wahlström, R. Walczak, P. A. Walker, K. Wang, A. Welsch, C. P. Welsch, S. M. Weng, S. M. Wiggins, J. Wolfenden, G. Xia, M. Yabashi, H. Zhang, Y. Zhao, J. Zhu, and A. Zigler
EuPRAXIA Conceptual Design Report
Eur. Phys. J. Special Topics, 229 :3675 (December 2020)
This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.
M. A. Leutenegger, S. Kuhn, P. Micke, R. Steinbrügge, J. Stierhof, C. Shah, N. Hell, M. Bissinger, M. Hirsch, R. Ballhausen, M. Lang, C. Gräfe, S. Wipf, R. Cumbee, G. L. Betancourt-Martinez, S. Park, V. A. Yerokhin, A. Surzhykov, W. C. Stolte, J. Niskanen, M. Chung, F. S. Porter, T. Stöhlker, T. Pfeifer, J. Wilms, G. V. Brown, J. R. C. Lopez-Urrutia, and S. Bernitt
High-Precision Determination of Oxygen Kα Transition Energy Excludes Incongruent Motion of Interstellar Oxygen
Phys. Rev. Lett., 125 :243001 (December 2020)
We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O2 with 8 meV uncertainty. We reveal a systematic ∼450  meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.
A. Steinkopff, C. Jauregui, C. Aleshire, A. Klenke, and J. Limpert
Impact of thermo-optical effects in coherently combined multicore fiber amplifiers
Opt. Express, 28 :38093 (December 2020)
In this work we analyze the power scaling potential of amplifying multicore fibers (MCFs) used in coherently combined systems. In particular, in this study we exemplarily consider rod-type MCFs with 2 × 2 up to 10 × 10 ytterbium-doped cores arranged in a squared pattern. We will show that, even though increasing the number of active cores will lead to higher output powers, particular attention has to be paid to arising thermal effects, which potentially degrade the performance of these systems. Additionally, we analyze the influence of the core dimensions on the extractable and combinable output power and pulse energy. This includes a detailed study on the thermal effects that influence the propagating transverse modes and, in turn, the amplification efficiency, the combining efficiency, the onset of nonlinear effect, as well as differences in the optical path lengths between the cores. Considering all these effects under rather extreme conditions, the study predicts that average output powers higher than 10 kW from a single 1 m long ytterbium-doped MCF are feasible and femtosecond pulses with energies higher than 400 mJ can be extracted and efficiently recombined in a filled-aperture scheme.
T. M. Ostermayr, C. Kreuzer, F. S. Englbrecht, J. Gebhard, J. Hartmann, A. Huebl, D. Haffa, P. Hilz, K. Parodi, J. Wenz, M. E. Donovan, G. Dyer, E. Gaul, J. Gordon, M. Martinez, E. Mccary, M. Spinks, G. Tiwari, B. M. Hegelich, and J. Schreiber
Laser-driven x-ray and proton micro-source and application to simultaneous single-shot bi-modal radiographic imaging
Nat. Commun., 11 :6174 (December 2020)
Radiographic imaging with x-rays and protons is an omnipresent tool in basic research and applications in industry, material science and medical diagnostics. The information contained in both modalities can often be valuable in principle, but difficult to access simultaneously. Laser-driven solid-density plasma-sources deliver both kinds of radiation, but mostly single modalities have been explored for applications. Their potential for bi-modal radiographic imaging has never been fully realized, due to problems in generating appropriate sources and separating image modalities. Here, we report on the generation of proton and x-ray micro-sources in laser-plasma interactions of the focused Texas Petawatt laser with solid-density, micrometer-sized tungsten needles. We apply them for bi-modal radiographic imaging of biological and technological objects in a single laser shot. Thereby, advantages of laser-driven sources could be enriched beyond their small footprint by embracing their additional unique properties, including the spectral bandwidth, small source size and multi-mode emission. Here the authors show a synchronized single-shot bi-modal x-ray and proton source based on laser-generated plasma. This source can be useful for radiographic and tomographic imaging.
F. Tuitje, P. Martinez Gil, T. Helk, J. Gautier, F. Tissandier, J. -P. Goddet, A. Guggenmos, U. Kleineberg, S. Sebban, E. Oliva, C. Spielmann, and M. Zuerch
Nonlinear ionization dynamics of hot dense plasma observed in a laser-plasma amplifier
Light Sci. Appl., 9 :187 (December 2020)
Understanding the behaviour of matter under conditions of extreme temperature, pressure, density and electromagnetic fields has profound effects on our understanding of cosmologic objects and the formation of the universe. Lacking direct access to such objects, our interpretation of observed data mainly relies on theoretical models. However, such models, which need to encompass nuclear physics, atomic physics and plasma physics over a huge dynamic range in the dimensions of energy and time, can only provide reliable information if we can benchmark them to experiments under well-defined laboratory conditions. Due to the plethora of effects occurring in this kind of highly excited matter, characterizing isolated dynamics or obtaining direct insight remains challenging. High-density plasmas are turbulent and opaque for radiation below the plasma frequency and allow only near-surface insight into ionization processes with visible wavelengths. Here, the output of a high-harmonic seeded laser-plasma amplifier using eight-fold ionized krypton as the gain medium operating at a 32.8 nm wavelength is ptychographically imaged. A complex-valued wavefront is observed in the extreme ultraviolet (XUV) beam with high resolution. Ab initio spatio-temporal Maxwell-Bloch simulations show excellent agreement with the experimental observations, revealing overionization of krypton in the plasma channel due to nonlinear laser-plasma interactions, successfully validating this four-dimensional multiscale model. This constitutes the first experimental observation of the laser ion abundance reshaping a laser-plasma amplifier. The presented approach shows the possibility of directly modelling light-plasma interactions in extreme conditions, such as those present during the early times of the universe, with direct experimental verification.
G. Torgrimsson
Nonlinear photon trident versus double Compton scattering and resummation of one-step terms
Phys. Rev. D, 102 :116008 (December 2020)
We study the photon trident process, where an initial photon turns into an electron-positron pair and a final photon under a nonlinear interaction with a strong plane-wave background field. We show that this process is very similar to double Compton scattering, where an electron interacts with the background field and emits two photons. We also show how the one-step terms can be obtained by resumming the small- and large -x expansions. We consider a couple of different resummation methods and also propose new resummations (involving Meijer-G functions) which have the correct type of expansions at both small and large x . These new resummations require relatively few terms to give good precision.
J. Wang, V. Bulanov, M. Chen, B. Lei, Y. X. Zhang, R. Zagidullin, V. Zorina, W. Yu, Y. Leng, R. Li, M. Zepf, and S. Rykovanov
Relativistic slingshot: A source for single circularly polarized attosecond x-ray pulses
Phys. Rev. E, 102 :061201 (December 2020)
We propose a mechanism to generate a single intense circularly polarized attosecond x-ray pulse from the interaction of a circularly polarized relativistic few-cycle laser pulse with an ultrathin foil at normal incidence. Analytical modeling and particle-in-cell simulation demonstrate that a huge charge-separation field can be produced when all the electrons are displaced from the target by the incident laser, resulting in a high-quality relativistic electron mirror that propagates against the tail of the laser pulse. The latter is efficiently reflected as well as compressed into an attosecond pulse that is also circularly polarized.
V. P. Kosheleva, V. A. Zaytsev, R. A. Müller, A. Surzhykov, and S. Fritzsche
Resonant two-photon ionization of atoms by twisted and plane-wave light
Phys. Rev. A, 102 :063115 (December 2020)
We study the resonant two-photon ionization of neutral atoms by a combination of twisted and plane-wave light within a fully relativistic framework. In particular, the ionization of an isotropic ensemble of neutral sodium atoms (Z = 11) from their ground 3 S-2(1/2) state via the 3 P-2(3/2) level is considered. We investigate in details the influence of the kinematic parameters of incoming twisted radiation on the photoelectron angular distribution and the circular dichroism. Moreover, we study the influence of the geometry of the process on these quantities. This is done by changing the propagation directions of the incoming twisted and plane-wave light. It is found that the dependence on the kinematic parameters of the twisted photon is the strongest if the plane-wave and twisted light beams are perpendicular to each other.
L. Stoyanov, M. Zhekova, A. Stefanov, I. Stefanov, G. Paulus, and A. Dreischuh
Zeroth- and first-order long range non-diffracting Gauss-Bessel beams generated by annihilating multiple-charged optical vortices
Sci. Rep., 10 :21981 (December 2020)
We demonstrate an alternative approach for generating zeroth- and first-order long range non-diffracting Gauss-Bessel beams (GBBs). Starting from a Gaussian beam, the key point is the creation of a bright ring-shaped beam with a large radius-to-width ratio, which is subsequently Fourier-transformed by a thin lens. The phase profile required for creating zeroth-order GBBs is flat and helical for first-order GBBs with unit topological charge (TC). Both the ring-shaped beam and the required phase profile can be realized by creating highly charged optical vortices by a spatial light modulator and annihilating them by using a second modulator of the same type. The generated long-range GBBs are proven to have negligible transverse evolution up to 2 m and can be regarded as non-diffracting. The influences of the charge state of the TCs, the propagation distance behind the focusing lens, and the GBB profiles on the relative intensities of the peak/rings are discussed. The method is much more efficient as compared to this using annular slits in the back focal plane of lenses. Moreover, at large propagation distances the quality of the generated GBBs significantly surpasses this of GBBs created by low angle axicons. The developed analytical model reproduces the experimental data. The presented method is flexible, easily realizable by using a spatial light modulator, does not require any special optical elements and, thus, is accessible in many laboratories.
B. Grabiger, B. Marx-Glowna, I. Uschmann, R. Loetzsch, G. Paulus, and K. Schulze
A highly sensitive imaging polarimeter in the x-ray regime
Appl. Phys. Lett., 117 :201102 (November 2020)
We report on the development of a highly sensitive imaging polarimeter that allows for the investigation of polarization changing properties of materials in the x-ray regime. By combining a microfocus rotating anode, collimating multilayer mirrors, and two germanium polarizer crystals, we achieved a polarization purity of the two orthogonal linear polarization states of 8 × 10−8. This enables the detection of an ellipticity on the same order or a rotation of the polarization plane of 6 arcsec. The high sensitivity combined with the imaging techniques allows us to study the microcrystalline structure of materials. As an example, we investigated beryllium sheets of different grades, which are commonly used for fabricating x-ray lenses, with a spatial resolution of 200 μm, and observed a strong degradation of the polarization purity due to the polycrystalline nature of beryllium. This makes x-ray lenses made of beryllium unsuitable for imaging polarimeter with higher spatial resolution. The results are important for the development of x-ray optical instruments that combine high spatial resolution and high sensitivity to polarization.
S. Panahiyan, and S. Fritzsche
Controllable simulation of topological phases and edge states with quantum walk
Phys. Lett. A, 384 :126828 (November 2020)
B. Baghdasaryan, and S. Fritzsche
Enhanced entanglement from Ince-Gaussian pump beams in spontaneous parametric down-conversion
Phys. Rev. A, 102 :052412 (November 2020)
Spontaneous parametric down-conversion (SPDC) has been a reliable process for the generation of entangled photon pairs. In this process, a nonlinear quadratic crystal is pumped by a laser field in order to convert (high-energy) photons into correlated photon pairs whose efficient control plays an essential role in various applications of quantum information processing. In particular, the amount of entanglement has been successfully controlled by adjusting the spatial structure of the incident pump field. Here, we theoretically analyze how the entanglement of the down-converted two-photon state can be further enhanced by using Ince-Gaussian beams with well-defined ellipticity epsilon, i.e., solutions of the paraxial wave equation in elliptical coordinates. These spatially structured beams are quite universal as they include both the Laguerre-Gaussian beams for epsilon -> 0 as well as the Hermite-Gaussian beams for epsilon -> infinity. We demonstrate that the entanglement of the generated photon pairs in SPDC can be maximized by a proper choice of epsilon and that such an enhanced entanglement can be observed experimentally in terms of the Schmidt number.
G. Torgrimsson
Nonlinear trident in the high-energy limit: Nonlocality, Coulomb field, and resummations
Phys. Rev. D, 102 :096008 (November 2020)
We study nonlinear trident in laser pulses in the high-energy limit, where the initial electron experiences, in its rest frame, an electromagnetic field strength above Schwinger s critical field. At lower energies the dominant contribution comes from the two-step' part, but in the high-energy limit the dominant contribution comes instead from the one-step term. We obtain new approximations that explain the relation between the high-energy limit of trident and pair production by a Coulomb field, as well as the role of the Weizsacker-Williams approximation and why it does not agree with the high-chi limit of the locally-constant-field approximation. We also show that the next-to-leading order in the large-a(0) expansion is, in the high-energy limit, nonlocal and is numerically very important even for quite large a(0). We show that the small-a(0) perturbation series has a finite radius of convergence, but using Pade-conformal methods we obtain resummations that go beyond the radius of convergence and have a large numerical overlap with the large-a(0) approximation. We use Borel-Pade-conformal methods to resum the small-chi expansion and obtain a high precision up to very large chi. We also use newer resummation methods based on hypergeometric/Meijer-G and confluent hypergeometric functions.
M. Togawa, S. Kuhn, C. Shah, P. Amaro, R. Steinbrügge, J. Stierhof, N. Hell, M. Rosner, K. Fujii, M. Bissinger, R. Ballhausen, M. Hoesch, J. Seltmann, S. Park, F. Grilo, F. S. Porter, J. P. Santos, M. Chung, T. Stöhlker, J. Wilms, T. Pfeifer, G. V. Brown, M. A. Leutenegger, S. Bernitt, and J. R. C. Lopez-Urrutia
Observation of strong two-electron–one-photon transitions in few-electron ions
Phys. Rev. A, 102 :052831 (November 2020)
We resonantly excite the K series of O5+ and O6+ up to principal quantum number n=11 with monochromatic x rays, producing K-shell holes, and observe their relaxation by soft-x-ray emission. Some photoabsorption resonances of O5+ reveal strong two-electron–one-photon (TEOP) transitions. We find that for the [(1s2s)15p3/2]3/2;1/2 states, TEOP relaxation is by far stronger than the radiative decay and competes with the usually much faster Auger decay path. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper states [(1s2p3/2)14s]3/2;1/2 of a Li-like satellite blend of the He-like Kα transition. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where electronic energy degeneracies are far more common and configuration mixing is stronger.
B. Böning, and S. Fritzsche
Partial-wave representation of the strong-field approximation
Phys. Rev. A, 102 :053108 (November 2020)
The strong-field approximation (SFA) has been widely applied to model ionization processes in short and intense laser pulses. Several approaches have been suggested in order to overcome certain limitations of the original SFA formulation with regard to the representation of the initial bound and final continuum states of the emitted electron as well as a suitable description of the driving laser pulse. We here present a reformulation of the SFA in terms of partial waves and spherical tensor operators that supports a quite simple implementation and the comparison of different treatments of the active (photo)electron and the laser pulses. In particular, this reformulation helps to adapt the SFA to experimental setups, and it paves the way to extend the strong-field theory toward the study of nondipole contributions in light-atom interactions as well as of many-particle correlations in strong-field ionization processes. A series of detailed computations have been carried out in order to confirm the validity of the reformulation and to show how the representation of the bound and continuum states affects the predicted above-threshold ionization spectra and related observables.
J. Deprince, M. A. Bautista, S. Fritzsche, J. A. García, T. R. Kallman, C. Mendoza, P. Palmeri, and P. Quinet
Plasma environment effects on K lines of astrophysical interest IV. IPs, K thresholds, radiative rates, and Auger widths in Fe ii-Fe viii
Astron. Astrophys., 643 :A57 (November 2020)
Aims. Within the framework of compact-object accretion disks, we calculate plasma environment effects on the atomic structure and decay parameters used in the modeling of K lines in lowly charged iron ions, namely FeII-FeVIII.Methods. For this study, we used the fully relativistic multiconfiguration Dirac-Fock method approximating the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel 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 10(5)-10(7) K and 10(18)-10(22) cm(-3). In addition, we propose two universal fitting formulae to predict the IP and K-threshold lowerings in any elemental ion.Conclusions. We conclude that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be able to detect the lowering of the K edges of these Fe ions due to the extreme plasma conditions occurring in the accretion disks around compact objects.