Highly efficient nonlinear compression of mJ pulses at 2 μm wavelength to 20 fs in a gas-filled multi-pass cell - Eisenbach, Lucas; Wang, Ziyao; Schulte, Jan; Heuermann, Tobias; Russb{\"{u}}ldt, Peter; Meyer, Rudolf; Gierschke, Philipp; Lenski, Mathias; Sugiura, Muneo; Tamura, Koichi; Limpert, Jens; H{\"{a}fner, Constantin (JPhys photonics, 2024)

In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy - Lenski, Mathias; Heuermann, Tobias; Wang, Ziyao; Aleshire, Christopher; Gaida, Christian; Jauregui, Cesar; Limpert, Jens (Optics letters, 2024)

Temperature and structure measurements of heavy-ion-heated diamond using in situ X-ray diagnostics - L{\"{u}}tgert, J.; Hesselbach, Philipp; Sch{\"{o}}rner, M.; Bagnoud, Vincent; Belikov, R.; Drechsel, P.; Heuser, B.; Humphries, O. S.; Katrik, Peter; Lindqvist, B.; Qu, C.; Redmer, R.; et al. (Matter and radiation at extremes, 2024)

Transport-property predictions for laser resonance chromatography on Rf + ( Z = 104 ) - Visentin, Giorgio; Ramanantoanina, Harry; Borschevsky, Anastasia; Viehland, Larry; Jana, Biswajit; Arya, Aayush; Fritzsche, Stephan; Laatiaoui, Mustapha (Physical review / A, 2024)

UV 30 fs laser pulse generation using a multi-pass cell - Hariton, Victor; Jiang, Yujiao; Sch{\"{o}}nberg, Arthur; Seidel, Marcus; Wieland, Marek; Prandolini, Mark J.; Hartl, Ingmar; Drescher, Markus; Heyl, Christoph (Optics letters, 2024)

Angle-resolved linear polarization of characteristic lines following innershell $2p_3/2$ photoionization of atoms - Wu, Zhongwen; Liu, W.; Fritzsche, S. (The European physical journal / D, 2024)

High-precision Transition Energy Measurements of Neon-like Fe xvii Ions - Shah, Chintan; Togawa, Moto; Botz, Marc; Danisch, Jonas; Goes, Joschka J.; Bernitt, Sonja; Maxton, Marleen; K{\"{o}}bnick, Kai; Buck, Jens; Seltmann, J{\"{o}}rn; Hoesch, Moritz; Gu, Ming Feng; et al. (The astrophysical journal / Part 1, 2024)

Inner-shell ionization cross sections of atoms by positron impact - Wang, Yuan-Cheng; Ma, Jia; Jiao, Li-Guang; Fritzsche, Stephan (Communications in theoretical physics, 2024)

Laser polarization control of ionization-injected electron beams and x-ray radiation in laser wakefield accelerators - Mukherjee, Arghya; Seipt, Daniel (Plasma physics and controlled fusion, 2024)

Merits of atomic cascade computations - Fritzsche, Stephan; Sahoo, Aloka Kumar; Sharma, L.; Wu, Zhongwen; Schippers, S. (The European physical journal / D, 2024)

Natural-linewidth measurements of the 3 C and 3 D soft-x-ray transitions in Ni xix - Shah, Chintan; K{\"{u}}hn, Steffen; Bernitt, Sonja; Steinbr{\"{u}}gge, Rene; Togawa, Moto; Berger, Lukas; Buck, Jens; Hoesch, Moritz; Seltmann, J{\"{o}}rn; Kozlov, Mikhail G.; Porsev, Sergey G.; Gu, Ming Feng; et al. (Physical review / A, 2024)

Novel signatures of radiation reaction in electron–laser sidescattering - Sikorski, Philipp; Thomas, Alec G R; Bulanov, Stepan S; Zepf, Matt; Seipt, Daniel (New journal of physics, 2024)

Nuclear quantum memory for hard x-ray photon wave packets - Velten, Sven; Bocklage, Lars; Zhang, Xiwen; Schlage, Kai; Panchwanee, Anjali; Sadashivaiah, Sakshath; Sergeev, Ilya; Leupold, Olaf; Chumakov, Aleksandr I.; Kocharovskaya, Olga; R{\"{o}}hlsberger, Ralf (Science advances, 2024)

p-wave resonances in the exponential cosine screened Coulomb potential* - Wang, Yuan-Cheng; Jiao, Li Guang; Liu, Aihua; Ho, Yew Kam; Fritzsche, Stephan (Communications in theoretical physics, 2024)

Revisiting the energy spectrum of the radial screened Coulomb potential - Xu, Lei; Fern{\'{a}}ndez, Francisco M; Jiao, Li Guang; Montgomery, Henry E; Ho, Yew Kam; Fritzsche, Stephan (Physica scripta, 2024)

All-optical source size and emittance measurements of laser-accelerated electron beams - Salgado, F. C.; Kozan, Alperen; Seipt, Daniel; Hollatz, D.; Hilz, P.; Kaluza, M.; S{\"{a}vert, A. and Seidel, A. and Ullmann, D. and Zhao, Y. and Zepf, M. (Physical review accelerators and beams, 2024)

Dark-field setup for the measurement of light-by-light scattering with high-intensity lasers - Sch{\"{u}}tze, Fabian; Doyle, Leonard; Schreiber, J{\"{o}}rg; Zepf, Matt; Karbstein, Felix (Physical review / D, 2024)

Fermionic fixed-point structure of asymptotically safe QED with a Pauli term - Gies, Holger; Tam, Kevin K. K. (The European physical journal / C, 2024)

Off-resonance electronic detection and cooling of ions in a Penning trap - Ringleb, Stefan; Kiffer, Markus; Vogel, Manuel; St{\"{o}}hlker, Thomas (The European physical journal / Plus, 2024)

Optical probing of ultrafast laser-induced solid-to-overdense-plasma transitions - Azamoum, Yasmina; Becker, Georg Alexander; Keppler, Sebastian; Duchateau, Guillaume; Skupin, Stefan; Grech, Mickael; Catoire, Fabrice; Hell, Sebastian; Tamer, Issa; Hornung, Marco; Hellwing, Marco; Kessler, Alexander; et al. (Light, 2024)

Single-Shot Diagnosis of Electron Energy Evolution via Streaked Betatron X Rays in a Curved Laser Wakefield Accelerator - Ma, Y.; Cardarelli, J. A.; Campbell, P. T.; Fourmaux, S.; Fitzgarrald, R.; Balcazar, M. D.; Antoine, A. F.; Beier, N. F.; Qian, Q.; Hussein, A. E.; Kettle, B.; Klein, S. R.; et al. (Physical review letters, 2024)

Towards ion stopping power experiments with the laser-driven LIGHT beamline - Nazary, Haress; Metternich, Martin; Schumacher, Dennis; Neufeld, F.; Grimm, S. J.; Brabetz, Christian; Kroll, F.; Brack, F.-E.; Blazevic, Abel; Schramm, U.; Bagnoud, Vincent; Roth, M. (Journal of plasma physics, 2024)

Application of a metallic-magnetic calorimeter for high-resolution x-ray spectroscopy of Fe at an EBIT - Herdrich, Marc Oliver; Hengstler, D.; Allgeier, S.; Friedrich, M.; Fleischmann, A.; Enss, C.; Bernitt, Sonja; Morgenroth, T.; Trotsenko, S.; Schuch, R.; St{\"{o}}hlker, Thomas (Journal of physics / B, 2024)

Bound state energies and critical bound region in the semiclassical dense hydrogen plasmas - Yan, Tong; Jiao, Li Guang; Liu, Aihua; Wang, Yuan Cheng; Montgomery, Henry E.; Ho, Yew Kam; Fritzsche, Stephan (Physics of plasmas, 2024)

Non-destructive depth reconstruction of Al-Al2Cu layer structure with nanometer resolution using extreme ultraviolet coherence tomography - Abel, Johann J.; Apell, Jonathan; Wiesner, Felix; Reinhard, Julius; W{\"{u}}nsche, Martin; Felde, Nadja; Schmidl, Gabriele; Plentz, Jonathan; Paulus, Gerhard G.; Lippmann, Stephanie; Fuchs, Silvio (Materials characterization, 2024)

Nonlinear interference and electron dynamics: Probing photoelectron momentum distributions in strong-field ionization - Dar, Danish Furekh; Fritzsche, Stephan (Physical review / A, 2024)

Relativistic R-matrix calculations for the photoionization of W61 + ions - Wu, Zhongwen; Wang, J. Q.; Li, Y.; An, Y. H.; Fritzsche, Stephan (Physics of plasmas, 2024)

Spectrally tunable phase-biased NALM mode-locked Yb:fiber laser with nJ-level pulse energy - Ebrahimzadeh, Saeid; Adnan, Sakib; Li, Yishen; Pecile, Vito F; Fellinger, Jakob; Salman, Haydar Sarper; Heyl, Christoph M; Hartl, Ingmar; Heckl, Oliver H; Porat, Gil (JPhys photonics, 2024)

The first in-beam reaction measurement at CRYRING@ESR using the CARME array - Marsh, Jordan J.; Bruno, Carlo G.; Davinson, Thomas; Woods, Philip J.; Andelkovic, Zoran; Br{\"{a}uning-Demian, Angela and Chen, Rui-Jui and Dellmann, Sophia F. and Erbacher, Phillip and Fedotova, Svetlana and Forstner, Oliver and Freire-Fernandez, David and Glorius, Jan and Gumberidze, Alexandre and Hall, Oscar and Hillenbrand, Pierre-Michel and Herfurth, Frank and Hudson-Chang, George and Kalinin, Anton and Lestinsky, Michael and Litvinov, Yuri A. and Menz, Esther B. and Nociforo, Chiara and Petridis, Nikolaos and Psaltis, Athanasios and Sanjari, Shahab and Selina, Mariia and Spillman, Uwe and Sidhu, Ragandeep S. and St{\"{o}}hlker, Thomas and Varga, Laszlo and Vorobjev, Gleb (The European physical journal / A, 2024)

Atomic photoexcitation as a tool for probing purity of twisted light modes - Schmidt, R. P.; Ramakrishna, S.; Peshkov, A. A.; Huntemann, N.; Peik, E.; Fritzsche, Stephan; Surzhykov, A. (Physical review / A, 2024)

Competition of the Breit interaction in angular anisotropy of Auger electrons - Wu, Zhongwen; Li, Y.; Fritzsche, Stephan (Physical review / A, 2024)

Rapid Access to Empirical Impact Ionization Cross Sections for Atoms and Ions across the Periodic Table - Fritzsche, Stephan; Jiao, Liguang; Visentin, Giorgio (Plasma, 2024)

Resistive cooling of ions' center-of-mass energy in a Penning trap on millisecond time scales - Kiffer, Markus; Ringleb, Stefan; St{\"{o}}hlker, Thomas; Vogel, Manuel (Physical review / A, 2024)

Acceleration correction to the binary-encounter Bethe model for the electron-impact ionization of molecules - Wang, Yuan-Cheng; Visentin, Giorgio; Jiao, Li Guang; Fritzsche, Stephan (Physical review / A, 2024)

Generalized binary-encounter-Bethe model for electron impact ionization of atoms - Wang, Yuan-Cheng; Jiao, Li Guang; Fritzsche, Stephan (Journal of physics / B, 2024)

Spectral properties of transverse Laguerre-Gauss modes in parametric down-conversion - Sevilla-Guti{\'{e}}rrez, Carlos; Kaipalath, Varun Raj; Baghdasaryan, Baghdasar; Gr{\"{a}fe, Markus and Fritzsche, Stephan and Steinlechner, Fabian (Physical review / A, 2024)

Towards the full Heisenberg-Euler effective action at large N - Karbstein, Felix (Journal of high energy physics, 2024)

Comparison of theory and experiment for radiative characteristics in neutral thulium - Bondarev, Andrey; Tamanis, Maris; Ferber, Ruvin; Ba{{s}}ar, G{\"{o}}n{\"{u}}l; Kr{\"{o}}ger, Sophie; Kozlov, Mikhail G.; Fritzsche, Stephan (Physical review / A, 2024)

Electron vortex generations in photoionization of hydrogen atoms by circularly-polarized chirped attosecond pulses - Zhang, Bingshuang; Liu, Xiaoyu; Zhu, Fengzheng; Jiao, Liguang; Liu, Aihua (Communications in theoretical physics, 2024)

Few-cycle laser pulse characterization on-target using high-harmonic generation from nano-scale solids - Awad, Mohanad; Manna, Apurba; Hell, Sebastian; Ying, Bo; {\'{A}}br{\'{o}}k, Levente; Div{\'{e}}ki, Zsolt; Cormier, Eric; Kiss, B{\'{a}}lint; B{\"{o}}hmer, Jan; Ronning, Carsten; Han, Seung Heon; George, Antony; et al. (Optics express, 2024)

High Inductance Cryogenic Current Comparators for Beamlines - Tympel, Volker; Machalett, Frank; St{\"{o}}hlker, Thomas; Crescimbeni, L.; Sch{\"{o}}nau, T.; Haider, David; Sieber, T.; Schwickert, Marcus; Schmidl, F.; Seidel, P.; Schmelz, M.; Stolz, R.; et al. (IEEE Transactions on Applied Superconductivity, 2024)

Polarization and CEP dependence of the transverse phase space in laser driven accelerators - Seidel, A.; Lei, Bifeng; Zepter, C.; Kaluza, M. C.; S{\"{a}vert, A. and Zepf, Karl Matth{\"{a}us and Seipt, Daniel (Physical review research, 2024)

Quantum dynamics of positron-hydrogen scattering and three-body bound state formation with an assisting laser field: predictions of a reduced-dimensionality model - Ji, Xiao Hu; Jiao, Li Guang; Liu, Aihua; Zhang, Yong Zhi; Thumm, Uwe; Ho, Yew Kam (Journal of physics / B, 2024)

Shot-to-shot electron beam pointing instability in a nonlinear plasma bubble - Lei, Bifeng; Liu, Bin; Shi, Mingyuan; Seidel, Andreas; Seipt, Daniel; Zepf, Matt; Qiao, Bin (Physical review / E, 2024)

Structured illumination ptychography and at-wavelength characterization with an EUV diffuser at 13.5 nm wavelength - Eschen, Wilhelm; Liu, Chang; Steinert, Michael; Penagos Molina, Daniel Santiago; Siefke, Thomas; Zeitner, Uwe D.; Kaspar, J{\"{o}}rg; Pertsch, Thomas; Limpert, Jens; Rothhardt, Jan (Optics express, 2024)

Exploring new states of matter with a photonic emulator - Karbstein, Felix; St{\"{u}}tzer, Simon; Gies, Holger; Szameit, Alexander (Physical review research, 2023)

Hyperfine-induced effects on the linear polarization of the magnetic-quadrupole lines of spin-1/2 Be-like ions excited by electron impact - Tian, Ziqiang; Tang, Zhiming; Li, Yi; Yang, Yang; Wu, Zhongwen; Zou, Yaming (Journal of quantitative spectroscopy ${ &}$ radiative transfer, 2023)

Position-sensitive non-destructive detection of charged-particle bunches in low-energy beamlines - Ringleb, Stefan; Kiffer, Markus; Ballentin, Jonas K. C.; St{\"{o}}hlker, Thomas; Vogel, Manuel (Scientific reports, 2023)

SPARC at FAIR: New Opportunities for Atomic Physics with Highly Charged Ions - Schuch, Reinhold; St{\"{o}}hlker, Thomas (Nuclear physics news, 2023)

A high-resolution asymmetric von Hamos spectrometer for low-energy X-ray spectroscopy at the CRYRING@ESR electron cooler - Jagodzinski, P.; Bana{ś}, D.; Pajek, M.; Kubala-Kuku{ś}, A.; Jab{ł}o{\'{n}}ski, {Ł}.; Stabrawa, I.; Szary, K.; Sobota, D.; Warczak, A.; Gumberidze, A.; Beyer, H. F.; Lestinsky, M.; et al. (Journal of Instrumentation, 2023)

Angular and polarization properties of characteristic x-ray radiation following inner-shell 2 p 3 / 2 photoionization of high- Z atoms - Wu, Zhongwen; Liu, W.; Fritzsche, Stephan (Physical review / A, 2023)

Complex diagnostic and numerical study of x-ray and particle emissions under relativistic ultra-short laser-solid interaction - Eftekhari-Zadeh, Ehsan; L{\"{o}}tzsch, Robert; Manganelli, Lorenzo; Bl{\"{u}}mcke, Manuel Sebastian; Tauschwitz, Anna; Uschmann, Ingo; Pukhov, Alexander; Rosmej, Olga; Spielmann, Christian; Kartashov, Daniil (Physica scripta, 2023)
Supported by COST under grant # CA21128

Dispersion engineering in nonlinear multipass cells for high-quality pulse compression - Karst, Maximilian; Benner, Maximilian; Gierschke, Philipp; Stark, Henning; Limpert, Jens (Optics letters, 2023)

Intensity-resolved measurement of above-threshold ionization of Ar − H 2 O - Platz, Adrian; Hell, Sebastian; Zhang, Yinyu; Ying, Bo; Paulus, Gerhard G.; K{\"{u}}bel, Matthias (Physical review / A, 2023)

Laboratory-Based Correlative Soft X-ray and Fluorescence Microscopy in an Integrated Setup - Reinhard, Julius; Kaleta, Sophia; Abel, Johann Jakob; Wiesner, Felix; W{\"{u}}nsche, Martin; Seemann, Eric; Westermann, Martin; Weber, Thomas; Nathanael, Jan; Iliou, Alexander; Fiedorowicz, Henryk; Hillmann, Falk; et al. (Microscopy and microanalysis, 2023)

Resonant X-ray excitation of the nuclear clock isomer 45Sc - Shvyd’ko, Yuri; R{\"{o}}hlsberger, Ralf; Kocharovskaya, Olga; Evers, J{\"{o}}rg; Geloni, Gianluca Aldo; Liu, Peifan; Shu, Deming; Miceli, Antonino; Stone, Brandon; Hippler, Willi; Marx-Glowna, Berit; Uschmann, Ingo; et al. (Nature, 2023)

Time-resolving state-specific molecular dissociation with XUV broadband absorption spectroscopy - Magunia, Alexander; Rebholz, Marc; Appi, Elisa; Papadopoulou, Christina C.; Lindenblatt, Hannes; Trost, Florian; Meister, Severin; Ding, Thomas; Straub, Michael; Borisova, Gergana D.; Lee, Junhee; Jin, Rui; et al. (Science advances, 2023)

Acousto-optic modulation of gigawatt-scale laser pulses in ambient air - Schr{\"{o}}del, Yannick Paul; Hartmann, Claas; Zheng, Jiaan; Lang, Tino; Steudel, Max; Rutsch, Matthias; Salman, Haydar Sarper; Kellert, Martin; Pergament, Mikhail; Hahn-Jose, Thomas; Suppelt, Sven; D{\"{o}}rsam, Jan Helge; et al. (Nature photonics, 2023)

Dielectronic recombination plasma rate coefficients of Na-, Mg-, and Al-like iron ions: The role of the 2(s + p) → 4 l , nl′ and 3(s + p) → 5 l , nl′ resonances - Visentin, Giorgio; Schippers, S.; Fritzsche, S. (Astronomy and astrophysics, 2023)

Insight into the prospective evaluation of third-order interelectronic corrections on Li-like ions - Soguel, R. N.; Fritzsche, Stephan (Physical review / A, 2023)

Low-energy tests of Delbr{\"{u}}ck scattering - Sommerfeldt, J.; Strnat, S.; Yerokhin, V. A.; Middents, Wilko; St{\"{o}}hlker, Thomas; Surzhykov, A. (Physical review / A, 2023)

Parametric study of the polarization dependence of nonlinear Breit–Wheeler pair creation process using two laser pulses - Qian, Qian; Seipt, Daniel; Vranic, Marija; Grismayer, Thomas E.; Blackburn, Thomas G.; Ridgers, Christopher P.; Thomas, Alexander G. R. (Physics of plasmas, 2023)

Parametric study of the polarization dependence of nonlinear Breit–Wheeler pair creation process using two laser pulses - Qian, Qian; Seipt, Daniel; Vranic, Marija; Grismayer, Thomas E.; Blackburn, Thomas G.; Ridgers, Christopher P.; Thomas, Alexander G. R. (Physics of Plasmas, 2023)
With the rapid development of high-power petawatt class lasers worldwide, exploring physics in the strong field QED regime will become one of the frontiers for laser–plasma interactions research. Particle-in-cell codes, including quantum emission processes, are powerful tools for predicting and analyzing future experiments where the physics of relativistic plasma is strongly affected by strong field QED processes. The spin/polarization dependence of these quantum processes has been of recent interest. In this article, we perform a parametric study of the interaction of two laser pulses with an ultrarelativistic electron beam. The first pulse is optimized to generate high-energy photons by nonlinear Compton scattering and efficiently decelerate electron beam through the quantum radiation reaction. The second pulse is optimized to generate electron–positron pairs by the nonlinear Breit–Wheeler decay of photons with the maximum polarization dependence. This may be experimentally realized as a verification of the strong field QED framework, including the spin/polarization rates.

Pauli-term-induced fixed points in d-dimensional QED - Gies, Holger; Tam, Kevin K. K.; Ziebell, Jobst (The European physical journal / C, 2023)

Resonances in the Hulth{\'{e}}n potential: benchmark calculations, critical behaviors, and interference effects - Hu, Zi Xi; Jiao, Li Guang; Liu, Aihua; Wang, Yuan Cheng; Montgomery Jr, Henry E; Ho, Yew Kam; Fritzsche, Stephan (Journal of physics / A, 2023)

Scalable angular spectrum propagation - Heintzmann, Rainer; Loetgering, Lars; Wechsler, Felix (Optica, 2023)

Hyperfine-induced effects on K$α_1$ linear polarization following electron-impact excitation of heliumlike Tl$^79+$ ions with nuclear spin I=1/2 - Wu, Z. W.; Tian, Z. Q.; Dong, C. Z.; Surzhykov, A.; Fritzsche, Stephan (New journal of physics, 2023)

Kinetic theory for spin-polarized relativistic plasmas - Seipt, Daniel; Thomas, Alec G. R. (Physics of Plasmas, 2023)
The investigation of spin and polarization effects in ultra-high intensity laser–plasma and laser–beam interactions has become an emergent topic in high-field science recently. In this paper, we derive a relativistic kinetic description of spin-polarized plasmas, where quantum-electrodynamics effects are taken into account via Boltzmann-type collision operators under the local constant field approximation. The emergence of anomalous precession is derived from one-loop self-energy contributions in a strong background field. We are interested, in particular, in the interplay between radiation reaction effects and the spin polarization of the radiating particles. For this, we derive equations for spin-polarized quantum radiation reaction from moments of the spin-polarized kinetic equations. By comparing with the classical theory, we identify and discuss the spin-dependent radiation reaction terms and radiative contributions to spin dynamics.

Post-compression of multi-millijoule picosecond pulses to few-cycles approaching the terawatt regime - Rajhans, Supriya; Escoto, Esmerando; Khodakovskiy, Nikita; Velpula, Praveen K.; Farace, Bonaventura; Grosse-Wortmann, Uwe; Shalloo, Rob J.; Arnold, Cord L.; Põder, Kristjan; Osterhoff, Jens; Leemans, Wim P.; Hartl, Ingmar; et al. (Optics letters, 2023)

Two-beam laser photon merging - Karbstein, Felix (Phys. Rev. D, 2023)

Ultrafast relativistic electron probing of extreme magnetic fields - Russell, Brandon K.; Campbell, Paul T.; Qian, Qian; Cardarelli, Jason A.; Bulanov, Stepan S.; Bulanov, Sergei V.; Grittani, Gabriele M.; Seipt, Daniel; Willingale, Louise; Thomas, Alexander G. R. (Physics of Plasmas, 2023)
We investigate the suitability of using GeV laser wakefield accelerated electron beams to measure strong, B { &}gt; 0.1 MT, magnetic fields. This method is explored as an alternative to proton deflectometry, which cannot be used for quantitative measurement using conventional analysis techniques at these extreme field strengths. Using such energetic electrons as a probe brings about several additional aspects for consideration, including beam divergence, detectors, and radiation reaction, which are considered here. Quantum radiation reaction on the probe is found to provide an additional measurement of the strength and length of fields, extending the standard deflectometry measurement that can only measure the path integrated fields. An experimental setup is proposed and measurement error is considered under near-term experimental conditions.

Storage, accumulation and deceleration of secondary beams for nuclear astrophysics - Glorius, Jan; Litvinov, Yu. A.; Aliotta, M.; Amjad, F.; Br{\"{u}}ckner, B.; Bruno, C. G.; Chen, R.; Davinson, T.; Dellmann, S. F.; Dickel, Timo; Dillmann, I.; Erbacher, P.; et al. (Nuclear instruments ${ &}$ methods in physics research / B, 2023)

Zernike-coefficient Extraction via Helical Beam Reconstruction for Optimization (ZEHBRO) in the far field - Ohland, Jonas Benjamin; Posor, D.; Eisenbarth, U.; Iancu, V.; Ungureanu, R.; Ursescu, D.; Bagnoud, Vincent (High power laser science and engineering, 2023)

Cusp-electron production in collisions of open-shell He-like oxygen ions with atomic targets - Nanos, S.; Esponda, N. J.; Hillenbrand, Pierre-Michel; Biniskos, A.; Laoutaris, A.; Quinto, M. A.; Petridis, Nikolaos; Menz, Esther Babette; Zouros, T. J. M.; St{\"{o}}hlker, Thomas; Rivarola, R. D.; Monti, J. M.; et al. (Physical review / A, 2023)

Optical vortices in brief: introduction for experimentalists - Stoyanov, Lyubomir; Topuzoski, Suzana; Paulus, Gerhard G.; Dreischuh, Alexander (The European physical journal / Plus, 2023)

Ultrafast Roaming Mechanisms in Ethanol Probed by Intense Extreme Ultraviolet Free-Electron Laser Radiation: Electron Transfer versus Proton Transfer - Wang, Enliang; Kling, Nora G; LaForge, Aaron C; Obaid, Razib; Pathak, Shashank; Bhattacharyya, Surjendu; Meister, Severin; Trost, Florian; Lindenblatt, Hannes; Schoch, Patrizia; K{\"{u}}bel, Matthias; Pfeifer, Thomas; et al. (The journal of physical chemistry letters, 2023)

Millijoule ultrafast optical parametric amplification as replacement for high-gain regenerative amplifiers - Zobus, Yannik; Brabetz, Christian; Hornung, Johannes; Ohland, Jonas Benjamin; Reemts, Dirk; Zou, Ji-Ping; Loeser, Markus; Albach, Daniel; Schramm, Ulrich; Bagnoud, Vincent (High power laser science and engineering, 2023)

Nearly isotropic Lyman-α1 radiation following nonradiative electron capture in Xe54+ + Kr collisions at 197 MeV u−1 - Yang, Bian; Wu, Z. W.; Yu, Deyang; Shao, Caojie; Xue, Yingli; Wang, Wei; Song, Zhangyong; Zhang, Mingwu; Liu, Junliang; Lu, Rongchun; Wu, Yehong; Ruan, Fangfang; et al. (Journal of Physics B: Atomic, Molecular and Optical Physics, 2023)
We measured the angular distribution of the subsequently emitted Lyman-α 1 transition of Xe53+* ions following nonradiative electron capture in collisions of 197 MeV u−1 Xe54+ projectiles with gaseous krypton target. The alignment of the projectile 2p 3/2 state and the relative population of its magnetic substates were further deduced. In contrast to the available lower energy results (Yang et al 2020 Phys. Rev. A 102 042803), it is found that at 197 MeV u−1 the Lyman-α 1 radiation becomes much less anisotropic and the magnetic substates are nearly statistically populated. Moreover, the experimental findings are compared with the results of the corresponding radiative electron capture mechanism, obviously different energy dependence of the magnetic-substate population is obtained and discussed using semiclassical arguments, which help reveal the population mechanism of excited states in collisions of highly charged high-Z ions with atoms.

22-W average power high pulse energy multipass-cell-based post-compression in the green spectral range - Karst, Maximilian; Pfaller, Pauline; Klas, Robert; Wang, Ziyao; Gierschke, Philipp; Rothhardt, Jan; Limpert, Jens (Optics letters, 2023)

Absolute measurement of the relativistic magnetic dipole transition in He-like sulfur - Machado, Jorge; Paul, Nancy; Soum-Sidikov, Gabrielle; Duval, Louis; Mac{\'{e}}, St{\'{e}}phane; L{\"{o}}tzsch, Robert; Trassinelli, Martino; Indelicato, Paul (Physical review / A, 2023)

Advances in QED with intense background fields - Fedotov, A.; Ilderton, A.; Karbstein, Felix; King, B.; Seipt, D.; Taya, H.; Torgrimsson, G. (Physics Reports, 2023)
Upcoming and planned experiments combining increasingly intense lasers and energetic particle beams will access new regimes of nonlinear, relativistic, quantum effects. This improved experimental capability has driven substantial progress in QED in intense background fields. We review here the advances made during the last decade, with a focus on theory and phenomenology. As ever higher intensities are reached, it becomes necessary to consider processes at higher orders in both the number of scattered particles and the number of loops, and to account for non-perturbative physics (e.g. the Schwinger effect), with extreme intensities requiring resummation of the loop expansion. In addition to increased intensity, experiments will reach higher accuracy, and these improvements are being matched by developments in theory such as in approximation frameworks, the description of finite-size effects, and the range of physical phenomena analysed. Topics on which there has been substantial progress include: radiation reaction, spin and polarisation, nonlinear quantum vacuum effects and connections to other fields including physics beyond the Standard Model.

All-Order Coulomb Corrections to Delbr{\"{u}}ck Scattering above the Pair-Production Threshold - Sommerfeldt, J.; Yerokhin, V. A.; St{\"{o}}hlker, Thomas; Surzhykov, A. (Physical review letters, 2023)
Supported by DFG under grant # SU 658/5-1.

Analysis of optical core-to-core coupling: challenges and opportunities in multicore fiber amplifiers - Steinkopff, Albrecht; Aleshire, Christopher; Klenke, Arno; Jauregui, Cesar; Limpert, Jens (Optics express, 2023)

Angle-differential cross sections for Rayleigh scattering of highly linearly polarized hard x rays on Au atoms - Middents, W.; Weber, G.; Gumberidze, A.; Hahn, C.; Krings, T.; Kurz, N.; Pf{\"{a}fflein, P. and Schell, N. and Spillmann, U. and Strnat, S. and Vockert, M. and Volotka, A. and Surzhykov, A. and St{\"{o}}hlker, T. (Physical Review A, 2023)
We perform a study on Rayleigh scattering of highly linearly polarized hard x rays on a thin Au foil target. In the study the angular distribution of the scattered radiation is analyzed in a relativistic regime both within and out of the plane of polarization of the incident beam. Within this experiment we scatter a synchrotron beam with a photon energy of 175 keV on a high-Z target foil, namely, gold. Our findings correlate well with state-of-the-art calculations of the scattering process performed in the framework of quantum electrodynamics and may have considerable impact on future experiments regarding a polarization-resolved analysis of Delbr{\"{u}}ck scattering. Furthermore, we show that the angular distribution of Rayleigh scattering can be used for a highly sensitive determination of the degree and orientation of the linear polarization of the incident hard-x-ray beam, if we rely on the theoretical framework.

Angular distribution of the characteristic line $1s2p ^3P_2 → 1s^2 ^1S_0$ of thallium ions: hyperfine-induced multipole interference - Wu, Sizhong; Tian, Z. Q.; Fritzsche, Stephan (The European physical journal / D, 2023)

Asymptotically safe Hilbert–Palatini gravity in an on-shell reduction scheme - Gies, Holger; Salek, Abdol Sabor (The European physical journal / C, 2023)

Below-threshold harmonic generation in gas-jets for Th-229 nuclear spectroscopy - Sch{\"{o}}nberg, Arthur; Salman, Haydar Sarper; Tajalli, Ayhan; Kumar, Sonu; Hartl, Ingmar; Heyl, Christoph (Optics express, 2023)

Broadband ptychography using curved wavefront illumination - Penagos Molina, Daniel Santiago; Loetgering, Lars; Eschen, Wilhelm; Limpert, Jens; Rothhardt, Jan (Optics express, 2023)
Supported by ESF and Free State of Thuringia under grant # 2018 FGR 0080. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License.

Calculation of Radiative Recombination Rates for Hydrogen-Like Ions at High-Z - Zhu, Binghui; St{\"{o}}hlker, Thomas (Proceedings of FAIR next generation scientists - 7th Edition Workshop {–} PoS(FAIRness2022) - Sissa Medialab Trieste, Italy, 2023. - ISBN - doi:10.22323/1.419.0065, 2023)

Calculations of multipole transitions in Sn II for kilonova analysis - Bondarev, Andrey; Gillanders, J. H.; Cheung, C.; Safronova, M. S.; Fritzsche, S. (The European physical journal / D, 2023)

CARME {–} The CRYRING Array for Reaction MEasurements - Bruno, C. G.; Marsh, J. J.; Davinson, T.; Woods, P. J.; Black, P.; Br{\"{a}uning-Demian, A. and Glorius, Jan and Grant, A. and Hall, O. and Headspith, A. and Hindley, P. and Lazarus, I. and Middleman, K. and Petridis, Nikolaos and Lestinsky, Michael and Litvinov, Yu. A. and Sidhu, R. S. and St{\"{o}}hlker, Thomas (Nuclear instruments ${ &}$ methods in physics research / A, 2023)

Characterization of transverse mode instability with a 4-quadrant photodiode - Kholaif, Sobhy; Jauregui, Cesar; Tu, Yiming; Limpert, Jens (Optics express, 2023)

Collision Strengths of Astrophysical Interest for Multiply Charged Ions - Fritzsche, Stephan; Jiao, Li-Guang; Wang, Yuan-Cheng; Sienkiewicz, Jozef E. (Atoms, 2023)

Collisional-radiative modeling of the 2p3 l ( l = p,d) spectra of N II and application to lightning - An, Yingying; Shen, Xiaozhi; Yuan, Ping; Wu, Zhongwen (Journal of applied physics, 2023)

Concept of enhanced frequency chirping for multi-pass cells to improve the pulse contrast - Benner, Maximilian; Karst, Maximilian; Amaya Mendez, Cristina; Stark, Henning; Limpert, Jens (Journal of the Optical Society of America / B, 2023)

Continuously tunable high photon flux high harmonic source at 50 – 70 eV - Kirsche, A.; Klas, R.; Gebhardt, M.; Eisenbach, L.; Eschen, W.; Buldt, J.; Stark, H.; Rothhardt, J.; Limpert, J. (Optics Express, 2023)
A fully tunable table-top extreme ultraviolet source providing state-of-the-art photon flux at energies of 50-70 eV is presented. It is based on a nonlinear blueshift and subsequent high harmonic generation in a gas-filled capillary.

Critical Laser Intensity of Phase-Matched High-Order Harmonic Generation in Noble Gases - Minneker, B.; Klas, R.; Rothhardt, J.; Fritzsche, S. (Photonics, 2023)
The efficient generation of high-order harmonic radiation has been a challenging task since the early days of strong-field physics. An essential requirement to achieve efficient high-order harmonic generation inside a gas medium is the phase matching of the high-order harmonic radiation and the incident laser pulse. The dominant contribution to the wave–vector mismatch Δk is associated with the ionization probability of the medium. In this work, we derive two analytical formulas to calculate the critical intensity of a general linearly polarized laser pulse that obey the phase-matching condition Δk=0. The analytic formulas are valid in the tunneling regime (ADK model) and the regime of the tunnel and multi-photon ionization (PPT model), respectively. We compare our results to numerical computations and discuss the scaling of the critical intensity depending on the pulse duration and the wavelength of a realistic incident laser pulse. The analytical approach demonstrated in this work is highly accurate and can compete with the existing numerical computational methods by an error of less than 1% and a decrease in the computation time of approximately 4 to 6 orders of magnitude. This enables complex theoretical studies of the efficiency scaling in HHG or to consider the effects of ground state depletion efficiently.
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Critical screening parameters of one-electron systems with screened Coulomb potentials: circular Rydberg states - Xu, Lei; Jiao, Li Guang; Liu, Aihua; Wang, Yuan Cheng; Montgomery Jr, Henry E; Ho, Yew Kam; Fritzsche, Stephan (Journal of physics / B, 2023)

Density-dependent carrier-envelope phase shift in attosecond pulse generation from relativistically oscillating mirrors - Zagidullin, Rishat; Tietze, Stefan; Zepf, Karl Matth{\"{a}us and Wang, Jingwei and Rykovanov, Sergey (Matter and radiation at extremes, 2023)
All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Dispersion-engineered multi-pass cell for single-stage post-compression of an ytterbium laser - Silletti, Laura; Wahid, Ammar; Escoto, Esmerando; Balla, Prannay; Rajhans, Supriya; Horn, Katinka; Winkelmann, Lutz; Wanie, Vincent; Trabattoni, Andrea; Heyl, Christoph; Calegari, Francesca (Optics letters, 2023)

Effective pressures on the outer-, inner-, and shell-confined hydrogenic atoms - Zhou, Zhi Ling; Jiao, Li Guang; Liu, Aihua; Wang, Yuan Cheng; Montgomery, Henry E.; Ho, Yew Kam; Fritzsche, Stephan (The European physical journal / D, 2023)

Energy spectra and asymptotic laws of the radial screened Coulomb potential - Xu, Lei; Jiao, Li Guang; Liu, Aihua; Montgomery, Henry E.; Ho, Yew Kam; Fritzsche, Stephan (Physics letters / A, 2023)

Enhancing the purity of single photons in parametric down-conversion through simultaneous pump-beam and crystal-domain engineering - Baghdasaryan, Baghdasar; Steinlechner, Fabian; Fritzsche, Stephan (Physical review / A, 2023)

Exploitation of the Timing Capabilities of Metallic Magnetic Calorimeters for a Coincidence Measurement Scheme - Pf{\"{a}fflein, P. and Weber, G. and Allgeier, S. and Bernitt, S. and Fleischmann, A. and Friedrich, M. and Hahn, C. and Hengstler, D. and Herdrich, M. and Kalinin, A. and Kr{\"{o}}ger, F. and Kuntz, P. and Lestinsky, M. and L{\"{o}}her, B. and Menz, E. and Spillmann, U. and Zhu, B. and Enss, C. and St{\"{o}}hlker, T. (Atoms, 2023)
In this report, we compare two filter algorithms for extracting timing information using novel metallic magnetic calorimeter detectors, applied to the precision X-ray spectroscopy of highly charged ions in a storage ring. Accurate timing information is crucial when exploiting coincidence conditions for background suppression to obtain clean spectra. For X-rays emitted by charge-changing interactions between ions and a target, this is a well-established technique when relying on conventional semiconductor detectors that offer a good temporal resolution. However, until recently, such a coincidence scheme had never been realized with metallic magnetic calorimeters, which typically feature much longer signal rise times. In this report, we present optimized timing filter algorithms for this type of detector. Their application to experimental data recently obtained at the electron cooler of CRYRING@ESR at GSI, Darmstadt is discussed.

Few-cycle pulse generation by double-stage hybrid multi-pass multi-plate nonlinear pulse compression - Viotti, Anne-Lise; Li, Chen; Arisholm, Gunnar; Winkelmann, Lutz; Hartl, Ingmar; Heyl, Christoph; Seidel, Marcus (Optics letters, 2023)

Frequency-doubled Q-switched 4 × 4 multicore fiber laser system - Aleshire, Christopher; Eichner, Timo; Steinkopff, Albrecht; Klenke, Arno; Jauregui, Cesar; Palmer, Guido; Kuhn, Stefan; Nold, Johannes; Haarlammert, Nicoletta; Leemans, Wim P.; Schreiber, Thomas; Maier, Andreas R.; et al. (Optics letters, 2023)

Geometric properties of the ground state of $H^-$ and $He$ in dense quantum plasmas - Li, Xue Nan; Zhang, Yong Zhi; Jiao, Li Guang; Wang, Yuan Cheng; Montgomery, Henry E.; Ho, Yew Kam; Fritzsche, Stephan (The European physical journal / D, 2023)

Gouy phase of Bessel-Gaussian beams: theory vs. experiment - Stoyanov, Lyubomir; Stefanov, Aleksander; Dreischuh, Alexander; Paulus, Gerhard G. (Optics express, 2023)

High-order above-threshold ionization in elliptically polarized laser fields: Identifying the recollision time - Chen, Zhangjin; Ding, Qiongmin; Chen, Qinghua; Li, Shuqi; Liu, Fang; Kang, Huipeng; Morishita, Toru; Chen, Jing (Physical review / A, 2023)

High-power two-color plasma-based THz generation driven by a Tm-doped fiber laser - Buldt, Joachim; Heuermann, Tobias; Wang, Ziyao; Gierschke, Philipp; Lenski, Mathias; Jauregui, Cesar; Limpert, Jens (Optics letters, 2023)
Supported by BMBF under grant # 01DR20009A and 13N15244.

High-resolution wavefront sensing and aberration analysis of multi-spectral extreme ultraviolet beams - Du, Mengqi; Liu, Xiaomeng; Pelekanidis, Antonios; Zhang, Fengling; L{\"{o}}tgering, Lars; Konold, Patrick; Porter, Christina L.; Smorenburg, Peter; Eikema, Kjeld S. E.; Witte, Stefan (Optica, 2023)

High-resolution X-ray emission study for Xe$^54+$ on Xe collisions - Herdrich, Marc Oliver; Hengstler, Daniel; Keller, Michael; Geist, Jeschua; Sch{\"{o}}tz, Christian; Krantz, Matth{\"{a}us and Fleischmann, Andreas and Enss, Christian and Gassner, Tobias and Hillenbrand, Pierre-Michel and Gumberidze, Alexandre and Spillmann, Uwe and Trotsenko, Sergiy and Indelicato, Paul and St{\"{o}}hlker, Thomas (The European physical journal / D, 2023)

High-speed and wide-field nanoscale table-top ptychographic EUV imaging and beam characterization with a sCMOS detector - Eschen, W.; Liu, C.; Penagos Molina, D.; Klas, R.; Limpert, J.; Rothhardt, J. (Optics Express, 2023)
We present high-speed and wide-field EUV ptychography at 13.5 nm wavelength using a table-top high-order harmonic source. Compared to previous measurements, the total measurement time is significantly reduced by up to a factor of five by employing a scientific complementary metal oxide semiconductor (sCMOS) detector that is combined with an optimized multilayer mirror configuration. The fast frame rate of the sCMOS detector enables wide-field imaging with a field of view of 100 µm × 100 µm with an imaging speed of 4.6 Mpix/h. Furthermore, fast EUV wavefront characterization is employed using a combination of the sCMOS detector with orthogonal probe relaxation.

Hyperpolarizabilities of hydrogenlike atoms in Debye and dense quantum plasmas - He, Yu Ying; Zhou, Zhi Ling; Jiao, Li Guang; Liu, Aihua; Montgomery, H. E.; Ho, Yew Kam (Physical review / E, 2023)

Image-Enhanced Pseudo-Thermal Ghost Imaging with Hybrid Speckle Pattern - Tian, Tong; Sun, Zhe; Oh, Sukyoon; Spielmann, Christian (Photonics, 2023)
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Imaging via Correlation of X-Ray Fluorescence Photons - Trost, Fabian; Ayyer, Kartik; Prasciolu, Mauro; Fleckenstein, Holger; Barthelmess, Miriam; Yefanov, Oleksandr; Dresselhaus, J. Lukas; Li, Chufeng; Bajt, Sa{{s}}a; Carnis, Jerome; Wollweber, Tamme; Mall, Abhishek; et al. (Physical review letters, 2023)

Implementation of a constant fraction algorithm for improved time resolution of metallic magnetic calorimeter measurements - Pf{\"{a}fflein, Philip and Hahn, Christoph and Herdrich, Marc Oliver and Kroeger, Felix Martin and Weber, G{\"{u}}nter and St{\"{o}}hlker, Thomas (Proceedings of FAIR next generation scientists - 7th Edition Workshop {–} PoS(FAIRness2022) - Sissa Medialab Trieste, Italy, 2023. - ISBN - doi:10.22323/1.419.0044, 2023)

Improvements of Computational Ghost Imaging by Using Sequenced Speckle - Oh, Sukyoon; Sun, Zhe; Tian, Tong; Spielmann, Christian (Applied Sciences, 2023)

Information scrambling and the correspondence of entanglement dynamics and operator dynamics in systems with nonlocal interactions - Wanisch, Darvin; Arias Espinoza, Juan Diego; Fritzsche, Stephan (Physical review / B, 2023)

Ionization in a laser-assisted ion-ion collision - Novak, O.; Kholodov, R.; Artemyev, A. N.; Surzhykov, A.; St{\"{o}}hlker, Thomas (Physical review / A, 2023)

Laser-accelerated electron beams at 1 GeV using optically-induced shock injection - Grafenstein, K.; Foerster, F. M.; Haberstroh, F.; Campbell, D.; Irshad, F.; Salgado, F. C.; Schilling, G.; Travac, E.; Wei{\"{s}}e, N.; Zepf, Karl Matth{\"{a}us and Dopp, A. and Karsch, S. (Scientific reports, 2023)

Mitigation of transverse mode instability by heat-load modulation - Kholaif, Sobhy; Jauregui, Cesar; Limpert, Jens (Optics express, 2023)

Nondipole strong-field approximation for above-threshold ionization in a few-cycle pulse - Dar, Danish Furekh; Minneker, Bj{\"{o}}rn; Fritzsche, Stephan (Physical review / A, 2023)

Nonlinear pulse compression to sub-two-cycle, 1.3 mJ pulses at 1.9 μm wavelength with 132 W average power - Wang, Ziyao; Heuermann, Tobias; Gebhardt, Martin; Lenski, Mathias; Gierschke, Philipp; Klas, Robert; Rothhardt, Jan; Jauregui, Cesar; Limpert, Jens (Optics letters, 2023)

Partial-wave representation of the strong-field approximation. II. Coulomb asymmetry in the photoelectron angular distribution of many-electron atoms - B{\"{o}}ning, Birger Nils; Fritzsche, Stephan (Physical review / A, 2023)

Probing bulk electron temperature via x-ray emission in a solid density plasma - Makur, K.; Ramakrishna, B.; Krishnamurthy, S.; Kakolee, K. F.; Kar, S.; Cerchez, M.; Prasad, R.; Markey, K.; Quinn, M. N.; Yuan, X. H.; Green, J. S.; Scott, R. H. H.; et al. (Plasma physics and controlled fusion, 2023)

Progress in Hybrid Plasma Wakefield Acceleration - Hidding, Bernhard; Assmann, Ralph; Bussmann, Michael; Campbell, David; Chang, Yen-Yu; Corde, S{\'{e}}bastien; Cabadağ, Jurjen Couperus; Debus, Alexander; D{\"{o}}pp, Andreas; Gilljohann, Max; G{\"{o}}tzfried, J.; Foerster, F. Moritz; et al. (Photonics, 2023)

PtyLab.m/py/jl: a cross-platform, open-source inverse modeling toolbox for conventional and Fourier ptychography - L{\"{o}}tgering, Lars; Du, Mengqi; Boonzajer Flaes, Dirk; Aidukas, Tomas; Wechsler, Felix; Penagos Molina, Daniel Santiago; Rose, Max; Pelekanidis, Antonios; Eschen, Wilhelm; Hess, J{\"{u}}rgen; Wilhein, Thomas; Heintzmann, Rainer; et al. (Optics express, 2023)

Pulse Cycle Dependent Nondipole Effects in Above-Threshold Ionization - Dar, Danish Furekh; Fritzsche, Stephan (Atoms, 2023)

Pulses of 32 mJ and 158 fs at 20-kHz repetition rate from a spatiotemporally combined fiber laser system - Stark, Henning; Benner, Maximilian; Buldt, Joachim; Klenke, Arno; Limpert, Jens (Optics letters, 2023)

Radiative recombination of highly charged ions with polarized electrons - Maiorova, Anna; Fritzsche, Stephan; Surzhykov, Andrey; St{\"{o}}hlker, Thomas (Physical review / A, 2023)

Radiative Recombination Plasma Rate Coefficients for Multiply Charged Ions - Fritzsche, Stephan; Maiorova, Anna; Wu, Zhongwen (Atoms, 2023)

Radiative Recombination Studies for Bare Lead Ions Interacting with Low-Energy Electrons - Zhu, Binghui; St{\"{o}}hlker, Thomas (Atoms, 2023)

Role of spatiotemporal couplings in stimulated Raman side scattering - Zepter, C.; Seidel, A.; Zepf, M.; Kaluza, M. C.; S{\"{a}vert, A. (Physical review research, 2023)

Self-broadening and self-shift in the $3v_2$ band of ammonia from mid-infrared-frequency-comb spectroscopy - Yang, Guang; Oliveira, Vinicius Silva; Laumer, Dominic; Heyl, Christoph M.; Yachmenev, Andrey; Hartl, Ingmar; K{\"{u}}pper, Jochen (Journal of molecular spectroscopy, 2023)

Spatial and temporal characteristics of spontaneous parametric down-conversion with varying focal planes of interacting beams - Bernecker, Richard; Baghdasaryan, Baghdasar; Fritzsche, Stephan (The European physical journal / D, 2023)
This article is licensed under a Creative Commons Attribution 4.0 International License

Spin-structured multilayer THz emitters by oblique incidence deposition - Kueny, Elias; Calendron, Anne-Laure; Velten, Sven; Bocklage, Lars; K{\"{a}rtner, Franz X. and R{\"{o}}hlsberger, Ralf (Journal of applied physics, 2023)

Stability of the $2p^2$ $^3P^e$ state of two-electron atoms near to critical nuclear charge - Zheng, Ruo Yu; Jiao, Li Guang; Liu, Aihua; Ma, Jia; Montgomery Jr, Henry E; Ho, Yew Kam; Fritzsche, Stephan (Journal of physics / B, 2023)

Strong configuration-interaction contributions to the angle-resolved $4_p$ photoelectron spectra of atomic xenon - Kosugi, S.; Koike, F.; Iizawa, M.; Hosseini, F.; Martins, J.; Marchenko, T.; Travnikova, O.; Bozek, J. D.; Ito, K.; Fritzsche, Stephan; Piancastelli, M. N.; Simon, M.; et al. (Physical review / A, 2023)

Sub-Hz relative linewidths from an interferometrically stabilized mid-infrared frequency comb - Laumer, Dominic; Salman, Haydar Sarper; Ma, Yuxuan; Zawilski, Kevin T.; Schunemann, Peter G.; Seidel, Marcus; Heyl, Christoph; Hartl, Ingmar (Optics letters, 2023)

Surprising Charge-Radius Kink in the Sc Isotopes at N = 20 - K{\"{o}}nig, Kristian; Fritzsche, Stephan; Hagen, Gaute; Holt, Jason D.; Klose, Andrew; Lantis, Jeremy; Liu, Yuan; Minamisono, Kei; Miyagi, Takayuki; Nazarewicz, Witold; Papenbrock, Thomas; Pineda, Skyy V.; et al. (Physical review letters, 2023)

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR - Kr{\"{o}}ger, F.; Weber, G.; Allgeier, S.; Andelkovic, Z.; Bernitt, S.; Borovik, A.; Duval, L.; Fleischmann, A.; Forstner, O.; Friedrich, M.; Glorius, J.; Gumberidze, A.; et al. (Atoms, 2023)
We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed.

Tracing spatial confinement in semiconductor quantum dots by high-order harmonic generation - Gopalakrishna, H. N.; Baruah, R.; H{\"{u}}necke, C.; Korolev, V.; Th{\"{u}}mmler, M.; Croy, A.; Richter, M.; Yahyaei, F.; Hollinger, R.; Shumakova, V.; Uschmann, I.; Marschner, H.; et al. (Physical review research, 2023)

Ultrafast serrodyne optical frequency translator - Balla, P.; Tuennermann, H.; Salman, S.; Fan, M.; Ali{{s}}auskas, S.; Hartl, I.; Heyl, C. (Nature Photonics, 2023)
The serrodyne principle enables an electromagnetic signal to be frequency shifted by applying a linear phase ramp in the time domain. This phenomenon has been exploited to frequency shift signals in the radiofrequency, microwave and optical regions of the electromagnetic spectrum over ranges of up to a few gigahertz, for example, to analyse the Doppler shift of radiofrequency signals for noise suppression and frequency stabilization. Here we employ this principle to shift the centre frequency of high-power femtosecond laser pulses over a range of several terahertz with the help of a nonlinear multi-pass cell. We demonstrate our method experimentally by shifting the central wavelength of a state-of-the-art 75 W frequency comb laser from 1,030 nm to 1,060 nm and to 1,000 nm. Furthermore, we experimentally show that this wavelength-shifting technique supports coherence characteristics at the few hertz-level while improving the temporal pulse quality. The technique is generally applicable to wide parameter ranges and different laser systems, enabling efficient wavelength conversion of high-power lasers to spectral regions beyond the gain bandwidth of available laser platforms.

Unveiling the inner structure of electron pulses generated from a laser-wakefield accelerator - Kaluza, Malte Christoph (Light, 2023)

Variational perturbation theory for dynamic polarizabilities and dispersion coefficients - Xia, Wen Hao; Zhou, Zhi Ling; Jiao, Li Guang; Liu, Aihua; Montgomery, Henry E.; Ho, Yew Kam; Fritzsche, Stephan (Physical review / E, 2023)

Versatile, compact chirped pulse amplifier pump system for ultrafast optical parametric amplifiers - Zobus, Yannik; Brabetz, Christian; Loeser, Markus; Albach, Daniel; Siebold, Mathias; Bagnoud, Vincent (Optics express, 2023)

Visualizing the ultra-structure of microorganisms using table-top extreme ultraviolet imaging - Liu, C.; Eschen, W.; Loetgering, L.; Molina, D.; Klas, R.; Iliou, A.; Steinert, M.; Herkersdorf, S.; Kirsche, A.; Pertsch, T.; Hillmann, F.; Limpert, J.; et al. (PhotoniX, 2023)
Table-top extreme ultraviolet (EUV) microscopy offers unique opportunities for label-free investigation of biological samples. Here, we demonstrate ptychographic EUV imaging of two dried, unstained model specimens: germlings of a fungus (Aspergillus nidulans), and bacteria (Escherichia coli) cells at 13.5 nm wavelength. We find that the EUV spectral region, which to date has not received much attention for biological imaging, offers sufficient penetration depths for the identification of intracellular features. By implementing a position-correlated ptychography approach, we demonstrate a millimeter-squared field of view enabled by infrared illumination combined with sub-60 nm spatial resolution achieved with EUV illumination on selected regions of interest. The strong element contrast at 13.5 nm wavelength enables the identification of the nanoscale material composition inside the specimens. Our work will advance and facilitate EUV imaging applications and enable further possibilities in life science.
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X-ray Spectroscopy Based on Micro-Calorimeters at Internal Targets of Storage Rings - Herdrich, M.; Hengstler, D.; Fleischmann, A.; Enss, C.; Gumberidze, A.; Hillenbrand, P.-M.; Indelicato, P.; Fritzsche, S.; St{\"{o}}hlker, T. (Atoms, 2023)
With metallic-magnetic calorimeters (MMCs), promising detectors for high-precision X-ray spectrometry in atomic and fundamental physics experiments are available. In this work, we present a pilot experiment based on a maXs-30 type MMC-spectrometer for recording X-rays emitted in collisions of lithium-like uranium ions with a molecular nitrogen gas jet in the internal target of the ESR storage ring of the GSI. Sample spectra have been measured, and a multitude of X-ray transitions have been unambiguously identified. As a first test and for comparison with data recorded at an EBIT, the 2s Lamb shift in lithium-like uranium was estimated.

Accelerating Ions by Crossing Two Ultraintense Lasers in a Near-Critical Relativistically Transparent Plasma - Liu, B.; Shi, M.; Zepf, M.; Lei, B.; Seipt, D. (Physical Review Letters, 2022)
A new scheme of ion acceleration by crossing two ultraintense laser pulses in a near-critical relativistically transparent plasma is proposed. One laser, acting as a trigger, preaccelerates background ions in its radial direction via the laser-driven shock. Another crossed laser drives a comoving snowplow field which traps some of the preaccelerated ions and then efficiently accelerates them to high energies up to a few giga-electron-volts. The final output ion beam is collimated and quasimonoenergetic due to a momentum-selection mechanism. Particle-in-cell simulations and theoretical analysis show that the scheme is feasible and robust.
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All-optical quantum vacuum signals in two-beam collisions - Gies, H.; Karbstein, F.; Klar, L. (Physical Review D, 2022)
We study the collision of two optical laser pulses in a pump-probe setup using beams with circular and elliptic cross section and estimate the number of discernible signal photons induced by quantum vacuum nonlinearities. In this analysis we study strategies to optimize the quantum vacuum signal discernible from the background of the driving lasers. One of the main results is that the collision of two maximally focused lasers does not lead to the best discernible signal. Instead, widening the focus typically improves the signal to background separation in the far field. For petawatt class lasers, an optimal choice of the focus waist yields several discernible photons per shot in contrast to no discernible signal for tight focusing. Further enhancement is possible by using an elliptical waist.
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Application of Symmetry-Adapted Atomic Amplitudes - Fritzsche, S. (Atoms, 2022)
Following the work of Giulio Racah and others from the 1940s onward, the rotational symmetry of atoms and ions, e.g., the conservation of angular momentum, has been utilized in order to efficiently predict atomic behavior, from their level structure to the interaction with external fields, and up to the angular distribution and polarization of either emitted or scattered photons and electrons, while this rotational symmetry becomes apparent first of all in the block-diagonal structure of the Hamiltonian matrix, it also suggests a straight and consequent use of symmetry-adapted interaction amplitudes in expressing the observables of most atomic properties and processes. We here emphasize and discuss how atomic structure theory benefits from exploiting this symmetry, especially if open-shell atoms and ions in different charge states need to be combined with electrons in the continuum. By making use of symmetry-adapted amplitudes, a large number of excitation, ionization, recombination or even cascade processes can be formulated rather independently of the atomic shell structure and in a language close to the formal theory. The consequent use of these amplitudes in existing codes such as Grasp will therefore qualify them to deal with the recently emerging demands for developing general-purpose tools for atomic computations.
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Background effective action with nonlinear massive gauge fixing - Gies, H.; Gkiatas, D.; Zambelli, L. (Physical Review D, 2022)
We combine a recent construction of a Becchi-Rouet-Stora-Tyutin (BRST)-invariant, nonlinear massive gauge fixing with the background field formalism. The resulting generating functional preserves background -field invariance as well as BRST invariance of the quantum field manifestly. The construction features BRST-invariant mass parameters for the quantum gauge and ghost fields. The formalism employs a background Nakanishi-Lautrup field which is part of the nonlinear gauge-fixing sector and thus should not affect observables. We verify this expectation by computing the one-loop effective action and the beta function of the gauge coupling as an example. The corresponding Schwinger functional generating connected correlation functions acquires additional one-particle reducible terms that vanish on shell. We also study off-shell one -loop contributions in order to explore the consequences of a nonlinear gauge fixing scheme involving a background Nakanishi-Lautrup field. As an application, we show that our formalism straightforwardly accommodates nonperturbative information about propagators in the Landau gauge in the form of the so-called decoupling solution. Using this nonperturbative input, we find evidence for the formation of a gluon condensate for sufficiently large coupling, whose scale is set by the BRST-invariant gluon mass parameter.
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Broadband soft X-ray source from a clustered gas target dedicated to high-resolution XCT and X-ray absorption spectroscopy - Janulewicz, K. A.; W{{e}}grzy{\'{n}}ski, {Ł}.; Fok, T.; Bartnik, A.; Fiedorowicz, H.; Skruszewicz, S.; W{\"{u}}nsche, M.; Eckner, E.; Fuchs, S.; Reinhard, J.; Abel, J. J.; Wiesner, F.; et al. (Optics Express, 2022)
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Circular Polarimetry of Hard X-rays with Rayleigh Scattering - Strnat, S.; Sommerfeldt, J.; Yerokhin, V.; Middents, W.; St{\"{o}}hlker, T.; Surzhykov, A. (Atoms, 2022)
We present a theoretical investigation of the elastic Rayleigh scattering of X-rays by atomic targets. Special attention is paid to the question of how the polarization of the scattered photons is affected if the incident light is itself polarized. In particular, we found that the circular polarization of the incoming X-rays may lead to a remarkable modification of the linear polarization of the scattered photons. Based on this extasciigrave circular-to-linear-polarization-transfer extquotesingle and on the fact that the linear polarization of X-rays can be conveniently observed by solid-state Compton detectors, we argue that Rayleigh scattering may be used as a tool for circular polarimetry of hard X-rays. To illustrate our proposal, we performed detailed calculations of 145 and 500 keV circularly polarized photons scattered by lead atoms. Based on these calculations, we found that the photon scattering under large angles with respect to the incident beam direction is most favorable for the circular polarimetry of hard X-rays. In particular, for 500 keV photon energy and scattering angles around 70 deg we found a remarkable modification of the linear polarization of scattered light for the case when the incident radiation is circularly polarized.
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Energy-loss enhancement and charge-equilibration time for highly charged xenon ions at near-Bohr velocity in solids - Song, Z. Y.; Wu, Z. W.; Yang, Z. H.; Zhang, B. L.; Xiao, G. Q. (Physical Review A, 2022)
We probe the energy-loss enhancement in preequilibration and the charge-equilibration time for highly charged Xe ions (qin = 15-26) at near-Bohr velocity impinging on an Al target by measuring the dependence of the Xe L-shell x-ray yield on the initial charge state of the ions. The present results are found to be very consistent with those obtained in ion-transmission thin-foil experiments. The charge-equilibrium time is measured in the near-Bohr velocity region of highly charged ions in solids. Moreover, for the present collision system it is demonstrated by measuring the inner-shell x rays that the ionization of the inner-shell electrons of the projectile ions starts to contribute to ion energy loss at near-Bohr velocity.
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First Experiments with CRYRING@ESR - Lestinsky, M.; Menz, E.; Danared, H.; Krantz, C.; Lindroth, E.; Andelkovic, Z.; Brandau, C.; Braeuning-Demian, A.; Fedotova, S.; Geithner, W.; Herfurth, F.; Kalinin, A.; et al. (Atoms, 2022)
The low-energy heavy ion storage ring CRYRING was transported from Stockholm to Darmstadt, modernized and reconfigured, and recommissioned as CRYRING@ESR. The machine is now in operation with all installations in service and is available as a user facility for experiments proposed through the SPARC collaboration. During the 2020-2022 period, we brought a number of experimental installations into service and used them to measure first data: the ultra-cold electron cooler for merged-beam electron-ion collisions, the gas jet target for atomic collisions, a next-generation microcalorimeter-based X-ray spectroscopy setup, and others. Ions can be injected either in low charge states from a local ion source through a 300 keV/u RFQ linac, or in high charge states from the GSI accelerator chain through ESR. This allows for very broad access to ions across the entire periodic table. CRYRING@ESR is able to de- or accelerate ions and cool and store beams of isotopically pure species in a desired charge state. While the analysis is still largely ongoing, the first experimental data already show that the machine reached its expected performance level, and our high expectations regarding achievable resolution in spectroscopy experiments have been fulfilled. With access to new classes of ions available through ESR injection and a new generation of experimental instrumentation, CRYRING@ESR is a unique facility for experiments with heavy, highly charged ions. Here, we will review our present setup and machine performance, discuss the data from our first commissioning experiments and briefly preview the upcoming new installations for the coming years.
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Generalized description of the spatio-temporal biphoton state in spontaneous parametric down-conversion - Baghdasaryan, B.; Sevilla-Gutierrez, C.; Steinlechner, F.; Fritzsche, S. (Physical Review A, 2022)
Spontaneous parametric down-conversion (SPDC) is a widely used source for photonic entanglement. Years of focused research have led to a solid understanding of the process, but a cohesive analytical description of the paraxial biphoton state has yet to be achieved. We derive a general expression for the spatio-temporal biphoton state that applies universally across common experimental settings and correctly describes the nonseparability of spatial and spectral modes. We formulate a criterion on how to decrease the coupling of the spatial from the spectral degree of freedom by taking into account the Gouy phase of interacting beams. This work provides new insights into the role of the Gouy phase in SPDC, and also into the preparation of engineered entangled states for multidimensional quantum information processing.
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Influence of Mechanical Deformations on the Performance of a Coaxial Shield for a Cryogenic Current Comparator - Marsic, N.; Mueller, W.; Tympel, V.; St{\"{o}}hlker, T.; Stapelfeld, M.; Schmidl, F.; Schmelz, M.; Zakosarenko, V.; Stolz, R.; Haider, D.; Sieber, T.; Schwickert, M.; et al. (IEEE Transactions on Applied Superconductivity, 2022)
This article studies the impact of mechanical deformations on the performance of a coaxial-type cryogenic current comparator (CCC). Such deformations may become a concern as the size of the CCC increases (e.g., when used as a diagnostic device in a particle accelerator facility involving beamlines with a large diameter). In addition to static deformations, this article also discusses the effect of mechanical vibrations on the CCC performance.
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Maximizing the validity of the Gaussian approximation for the biphoton state from parametric down-conversion - Baghdasaryan, B.; Steinlechner, F.; Fritzsche, S. (Physical Review A, 2022)
Spontaneous parametric down-conversion (SPDC) is widely used in quantum applications based on photonic entanglement. The efficiency of photon pair generation is often characterized by means of a sinc(L delta k/2) function, where L is the length of the nonlinear medium and delta k is the phase mismatch between the pump and down-converted fields. In theoretical investigations, the sinc behavior of the phase mismatch has often been approximated by a Gaussian function exp (-alpha x(2)) in order to derive analytical expressions for the SPDC process. Different values have been chosen in the literature for the optimization factor alpha, for instance, by comparing the widths of sinc and Gaussian functions or the momentum of down-converted photons. As a consequence, different values of alpha provide different theoretical predictions for the same setup. Therefore an informed and unique choice of this parameter is necessary. In this paper, we present a choice of alpha which maximizes the validity of the Gaussian approximation. Moreover, we also discuss the so-called super-Gaussian and cosine-Gaussian approximations as practical alternatives with improved predictive power for experiments.
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New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem - Kuhn, S.; Cheung, C.; Oreshkina, N. S.; Steinbr{\"{u}}gge, R.; Togawa, M.; Bernitt, S.; Berger, L.; Buck, J.; Hoesch, M.; Seltmann, J.; Trinter, F.; Keitel, C. H.; et al. (Physical Review Letters, 2022)
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Performance of a keV/u Ion Spectrometer for the FISIC Platform - Jolly, M.; Voikopoulos, S.; Lamour, E.; M{\'{e}}ry, A.; Braeuning-Demian, A.; Chesnel, J.-Y.; Gumberidze, A.; Lestinsky, M.; Mac{\'{e}}, S.; Prigent, C.; Ramillon, J.-M.; Rangama, J.; et al. (Atoms, 2022)
The design and performances of a newly built electrostatic charge state analyzer constructed to act as a spectrometer for keV/u ions are reported. It consists of two 90 { &} LCIRC; curved electrodes enclosed by Matsuda electrodes. This setup was recently tested using Ar9+ and Ar12+ ion beams at an energy of 10 keV per charge unit. This spectrometer achieves a good separation of different charge states formed by electron capture processes during collisions between primary ions and the residual gas. Thanks to these first tests, we have identified up to three different background contributions on the detector that need to be reduced or suppressed.
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Raman-based detection of ciprofloxacin and its degradation in pharmaceutical formulations - Liu, C.; Mueller-Botticher, L.; Popp, J.; Fischer, D.; Cialla-May, D. (Talanta, 2022)
A Raman-based label-free analytical method was developed to detect the antibiotic ciprofloxacin (CIP) in various pharmaceutical formulations in the presence of different matrices (e.g., ear drops, eye drops and infusion solutions). The Raman spectral analysis is performed for semiquantification in the case of a low background Raman signal, i.e., the signal originating from the excipient and carrier substance of the formulation does not interfere with the fingerprint spectrum of ciprofloxacin. In the case of a background spectrum rich in Raman modes originating from the excipient and carrier substance of the formulation, the pharmaceutical formulation is diluted 1:5000, and thus, the background signal is undetectable. Due to the high affinity of ciprofloxacin towards metallic surfaces, surface-enhanced Raman spectroscopy (SERS) is applied to allow for the sensitive detection of ciprofloxacin. Moreover, the developed measurement routine can be applied to monitor the degradation of the active component ciprofloxacin within the pharmaceutical formulation. The developed assay can therefore be extended to the pharmaceutical industry for quality control in assay applications or the preparation of individualized medicines.
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X-Ray Photoabsorption of Density-sensitive Metastable States in Ne vii, Fe xxii, and Fe xxiii - Steinbr{\"{u}}gge, R.; Kuehn, S.; Nicastro, F.; Gu, M.; Togawa, M.; Hoesch, M.; Seltmann, J.; Sergeev, I.; Trinter, F.; Bernitt, S.; Shah, C.; Leutenegger, M.; et al. (Astrophysical Journal, 2022)
Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify K alpha transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 10(10.5) cm(-3).
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Analyzing the filamentation of MeV-range proton bunches in a laser-driven ion beamline and optimizing their peak intensity - Metternich, M.; Nazary, H.; Schumacher, D.; Brabetz, C.; Kroll, F.; Brack, F.-E.; Ehret, M.; Blazevic, A.; Schramm, U.; Bagnoud, V.; Roth, M. (Physical Review Accelerators and Beams, 2022)
In this article, we report on the latest investigations and achievements in proton beam shaping with our laser-driven ion beamline at GSI Helmholtzzentrum fiir Schwerionenforschung GmbH. This beamline was realized within the framework of the Laser Ion Generation, Handling, and Transport (LIGHT) collaboration to study the combination of laser-driven ion beams with conventional accelerator components. At its current state, the ions are accelerated by the high-power laser PHELIX via target normal sheath acceleration, and two pulsed high-magnetic solenoids are used for energy selection, transport, and transverse focusing. In between the two solenoids, there is a rf cavity that gives the LIGHT beamline the capability to longitudinally manipulate and temporally compress ion bunches to sub-nanosecond durations. To get optimal results, the rf cavity has to be synchronized with the PHELIX laser and therefore a reliable measurement of the temporal ion beam profile is necessary. In the past, these measurements showed unexpected correlations between the temporal beam profile and the phase as well as the electric field strength of the cavity. In this article, we present a numerical simulation of the beam transport through the LIGHT beamline which explains this behavior by a beam filamentation. We also report on our latest experimental campaigns, in which we combined transverse and longitudinal focusing for the first time. This led to proton bunches with a peak intensity of (3.28 +/- 0.24) x 10(8) protons/ (ns mm(2)) at a central energy of (7.72 +/- 0.14) MeV. The intensity refers to a circle with a diameter of (1.38 +/- 0.02) mm that encloses 50% of the protons in the focal spot at the end of the beamline. The temporal bunch width at this position was (742 +/- 40) ps (FWHM).
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Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy - Schwickert, D.; Ruberti, M.; Kolorenc, P.; Przystawik, A.; Skruszewicz, S.; Sumfleth, M.; Braune, M.; Bocklage, L.; Carretero, L.; Czwalinna, M.; Diaman, D.; Duesterer, S.; et al. (Structural Dynamics, 2022)
In the present contribution, we use x-rays to monitor charge-induced chemical dynamics in the photoionized amino acid glycine with femtosecond time resolution. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay. Temporal modulation of the Auger electron signal correlated with specific ions is observed, which is governed by the initial electronic coherence and subsequent vibronic coupling to nuclear degrees of freedom. In the time-resolved x-ray absorption measurement, we monitor the time-frequency spectra of the resulting many-body quantum wave packets for a period of 175 fs along different reaction coordinates. Our experiment proves that by measuring specific fragments associated with the glycine dication as a function of the pump-probe delay, one can selectively probe electronic coherences at early times associated with a few distinguishable components of the broad electronic wave packet created initially by the pump pulse in the cation. The corresponding coherent superpositions formed by subsets of electronic eigenstates and evolving along parallel dynamical pathways show different phases and time periods in the range of (-0.3 +/- 0.1 ) pi <= phi <= ( 0.1 +/- 0.2 ) pi and 18.2(-1.4)(+1.7) <= T <= 23.9(-1.1)(+1.2 )fs. Furthermore, for long delays, the data allow us to pinpoint the driving vibrational modes of chemical dynamics mediating charge-induced bond cleavage along different reaction coordinates. (C) 2022 Author(s).
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Determination of the reflectivity of crystals by ptychography - Schulze, K. S. (AIP Advances, 2022)
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Generalized nondipole strong-field approximation of high-order harmonic generation - Minneker, B.; Boening, B.; Fritzsche, S. (Physical Review A, 2022)
The strong-field approximation (SFA) is a widely used theoretical framework that describes the process of high-order harmonic generation of atoms and molecules. Here, we propose a generalization of the dipole SFA towards weakly relativistic contributions to the laser-electron interaction. These weakly relativistic contributions are closely related to the spatial structure of the light field and imply a correction of the relativistic order 1/c. Within this generalized nondipole SFA (GN-SFA), we demonstrate how to obtain explicit results and discuss their physical aspects. This approach enables one to investigate the nondipole effects of linear polarized plane waves as well as the influence of structured light fields, such as twisted light, that have not yet been captured by the currently available models. In order to utilize our generalized nondipole SFA, we consider a linearly polarized plane wave and demonstrate the decrease of the harmonic yield that is directly related to the nondipole effects of the laser field. Furthermore, we discuss the GN-SFA with regard to other nondipole SFA approaches by determining their physical and mathematical context. Finally, the GN-SFA is a powerful theoretical framework that extends the nonrelativistic SFA rigorously to the weakly relativistic regime and therefore will be a useful model for further theoretical investigations.
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How to optimize high-order harmonic generation in gases - Weissenbilder, R.; Carlstrom, S.; Rego, L.; Guo, C.; Heyl, C. M.; Smorenburg, P.; Constant, E.; Arnold, C. L.; L'Huillier, A. (Nature Reviews Physics, 2022)
High-order harmonic generation (HHG) in gases leads to short-pulse extreme ultraviolet (XUV) radiation that is useful in a number of applications, such as attosecond science and nanoscale imaging. However, this process depends on many parameters, and there is still no consensus on how to choose the target geometry to optimize the source efficiency. We review the physics of HHG with emphasis on the macroscopic aspects of the nonlinear interaction, discussing the influence of length of medium, pressure, and intensity of the driving laser on the HHG conversion efficiency. Efficient HHG can be realized over a large range of pressures and medium lengths, if these follow a certain hyperbolic equation. This explains the large versatility in gas target designs for efficient HHG and provides design guidance for future high-flux XUV sources.
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Inband-pumped, high-power thulium-doped fiber amplifiers for an ultrafast pulsed operation - Lenski, M.; Heuermann, T.; Gebhardt, M.; Wang, Z.; Gaida, C.; Jauregui, C.; Limpert, J. (Optics Express, 2022)
We investigate the influence of the pump wavelength on the high-power amplification of large-mode area, thulium-doped fibers which are suitable for an ultrashort pulsed operation in the 2 mu m wavelength region. By pumping a standard, commercially available photonic crystal fiber in an amplifier configuration at 1692 nm, a slope efficiency of 80 % at an average output power of 60 W could be shown. With the help of simulations we investigate the effect of cross-relaxations on the efficiency and the thermal behavior. We extend our investigations to a rod-type, large-pitch fiber with very large mode area, which is exceptionally suited for high-energy ultrafast operation. Pumping at 1692 nm leads to a slope efficiency of 74% with a average output power of 67 W, instead of the 38 % slope efficiency obtained when pumping at 793 nm. These results pave the way to highly efficient 2 mu m fiber-based CPA systems.
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Integration of maXs-type microcalorimeter detectors for high-resolution x-ray spectroscopy into the experimental environment at the CRYRING@ESR electron cooler - Pf{\"{a}fflein, P. and Allgeier, S. and Bernitt, S. and Fleischmann, A. and Friedrich, M. and Hahn, C. and Hengstler, D. and Herdrich, M. O. and Kalinin, A. and Kr{\"{o}}ger, F. M. and Kuntz, P. and Lestinsky, M. and Loeher, B. and Menz, E. B. and Over, T. and Spillmann, U. and Weber, G. and Zhu, B. and Enss, C. and St{\"{o}}hlker, T. (Physica Scripta, 2022)
We report on the first integration of novel magnetic microcalorimeter detectors (MMCs), developed within SPARC (Stored Particles Atomic Physics Research Collaboration), into the experimental environment of storage rings at GSI(6), Darmstadt, namely at the electron cooler of CRYRING@ESR. Two of these detector systems were positioned at the 0 degrees and 180 degrees view ports of the cooler section to obtain high-resolution x-ray spectra originating from a stored beam of hydrogen-like uranium interacting with the cooler electrons. While previous test measurements with microcalorimeters at the accelerator facility of GSI were conducted in the mode of well-established stand-alone operation, for the present experiment we implemented several notable modifications to exploit the full potential of this type of detector for precision x-ray spectroscopy of stored heavy ions. Among these are a new readout system compatible with the multi branch system data acquisition platform of GSI, the synchronization of a quasi-continuous energy calibration with the operation cycle of the accelerator facility, as well as the first exploitation of the maXs detectors time resolution to apply coincidence conditions for the detection of photons and charge-changed ions.
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Monitoring of the heavy-ion beam distribution using poly- and monochromatic x-ray fluorescence imaging - Z{\"{a}hter, S. and Rosmej, O. N. and Beloiu, P. and Bogdanov, A. and Golubev, A. and Gyrdymov, M. and Jacoby, J. and Kantsyrev, A. and Loetzsch, R. and Nicolai, M. and Panyushkin, V. and Skobliakov, A. and Tavana, P. M. and Uschmann, I. and Zahn, N. and Spielmann, C. (Review of Scientific Instruments, 2022)
In this work, the first proof of the principal of an in situ diagnostics of the heavy-ion beam intensity distribution in irradiation of solid targets is proposed. In this scheme, x-ray fluorescence that occurs in the interaction of heavy-ions with target atoms is used for imaging purposes. The x-ray conversion to optical radiation and a transport-system was developed, and its first test was performed in experiments at the Universal Linear Accelerator in Darmstadt, Germany. The Au-beam intensity distribution on thin foils and Cu-mesh targets was imaged using multiple x-ray pinholes (polychromatic imaging) and 2D monochromatic imaging of Cu Kα radiation by using a toroidally bent silicon crystal. The presented results are of importance for application in experiments on the investigation of the equation of states of high energy density matter using high intensity GeV/u heavy-ion beams of ≥10^10 particles/100 ns.
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Biharmonic (omega, 2 omega) ionization of atoms by elliptically-polarized light. Carving the photoelectron angular distributions - Fritzsche, S.; Hofbrucker, J. (New Journal of Physics, 2022)
The biharmonic (omega, 2 omega) photoionization of atomic inner-shell electrons opens up new perspectives for studying nonlinear light-atom interactions at intensities in the transition regime from weak to strong-field physics. In particular, the control of the frequency and polarization of biharmonic beams enables one to carve the photoelectron angular distribution and to enhance the resolution of ionization measurements by the (simultaneous) absorption of photons. Apart from its quite obvious polarization dependence, the photoelectron angular distributions are sensitive also to the (relative) intensity, the phase difference and the temporal structure of the incoming beam components, both at resonant and nonresonant frequencies. Here, we describe and analyze several characteristic features of biharmonic ionization in the framework of second-order perturbation theory and (so-called) ionization pathways, as they are readily derived from the interaction of inner-shell electrons with the electric-dipole field of the incident beam. We show how the photoelectron angular distribution and elliptical dichroism can be shaped in rather an unprecedented way by just tuning the properties of the biharmonic field. Since such fields are nowadays accessible from high-harmonic sources or free-electron lasers, these and further investigations might help extract photoionization amplitudes or the phase difference of incoming beams.
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Nonsequential double ionization of Ne with elliptically polarized laser pulses - Liu, F.; Li, S.; Chen, Z.; B{\"{o}}ning, B.; Fritzsche, S. (Physical Review A, 2022)
We show through simulation that the improved quantitative rescattering model (QRS) can successfully predict the nonsequential double ionization (NSDI) process by intense elliptically polarized laser pulses. Using the QRS model, we calculate the correlated two-electron and ion momentum distributions of NSDI in Ne exposed to intense elliptically polarized laser pulses with a wavelength of 788 nm at a peak intensity of 5.0 x 10(14) W/cm(2). We analyze the asymmetry in the doubly charged ion momentum spectra observed by Kang et al. [Phys. Rev. Lett. 120, 223204 (2018)] in going from linearly to elliptically polarized laser pulses. Our model reproduces the experimental data well. Furthermore, we find that the ellipticity-dependent asymmetry arises from the drift velocity along the minor axis of the elliptic polarization. We explain how the correlated electron momentum distributions along the minor axis provide access to the subcycle dynamics of recollision. From these findings, we expect that we can extend the QRS model for NSDI toward more complicated laser fields in the future.
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Spectrally tunable high-power Yb:fiber chirped-pulse amplifier - Shumakova, V.; Pecile, V.; Fellinger, J.; Leskowschek, M.; Aldia, P.; Mayer, A.; Perner, L.; Salman, S.; Fan, M.; Balla, P.; Schilt, S.; Heyl, C.; et al. (Photonics Research, 2022)
Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser, and therefore high average power, pulse duration of a few tens of fs, and maximal available spectral bandwidth. Contrarily, the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations. Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification (CPA) to the requirements of different nonlinear frequency converters while preserving the low-phase-noise (PN) properties of the system. To achieve spectral tunability, we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system. The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz. While gaining control over the spectral properties, we preserve the relative-intensity-noise and PN properties of the system. The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation (full width at half maximum of similar to 11 nm, compressed pulse duration of 230 fs) or a spectrum ideal for highly nonlinear processes such as high-harmonic generation (-10 dB level of >50 nm, transform-limited pulse duration of similar to 65 fs).
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Steering the longitudinal photoelectron momentum in the above-threshold ionization with two not-quite-collinear laser beams - B{\"{o}}ning, B.; Fritzsche, S. (Physical Review A, 2022)
Strong-field atomic processes, driven by long-wavelength laser beams, are known to be affected by magnetic forces. In such beams, the Lorentz force pushes the photoelectrons along the beam direction and prevents their rescattering or recombination with the parent ions. In high-order harmonic generation (HHG), therefore, the yield of energetic photons is markedly suppressed, rendering x-ray radiation sources from high harmonics so far impractical. To compensate these magnetic forces and to reenable HHG at long wavelengths, a setup of two not quite collinear beams has been suggested recently but not much analyzed beyond classical arguments and with respect to accessible laser parameters. Using the nondipole strong-field approximation, we here investigate when the longitudinal momentum of the photoelectrons vanishes and how this noncollinear setup explicitly depends on the wavelength and intensity of the driving beams. We also demonstrate that an optimal crossing angle delta 0 between these beams always exists for which the fraction of the returning electrons is maximized. This rather simple steering of the longitudinal momentum will allow an efficient HHG with driving beams deep in the midinfrared.
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Absolute EUV reflectivity measurements using a broadband high-harmonic source and an in situ single exposure reference scheme - Abel, J.; Wiesner, F.; Nathanael, J.; Reinhard, J.; W{\"{u}}nsche, M.; Schmidl, G.; Gawlik, A.; Huebner, U.; Plentz, J.; R{\"{o}}del, C.; Paulus, G.; Fuchs, S. (Optics Express, 2022)
We present a tabletop setup for extreme ultraviolet (EUV) reflection spectroscopy in the spectral range from 40 to 100 eV by using high-harmonic radiation. The simultaneous measurements of reference and sample spectra with high energy resolution provide precise and robust absolute reflectivity measurements, even when operating with spectrally fluctuating EUV sources. The stability and sensitivity of EUV reflectivity measurements are crucial factors for many applications in attosecond science, EUV spectroscopy, and nano-scale tomography. We show that the accuracy and stability of our in situ referencing scheme are almost one order of magnitude better in comparison to subsequent reference measurements. We demonstrate the performance of the setup by reflective near-edge x-ray absorption fine structure measurements of the aluminum L2/3 absorption edge in alpha-Al2O3 and compare the results to synchrotron measurements.
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Saturable Absorption of Free-Electron Laser Radiation by Graphite near the Carbon K-Edge - Hoffmann, L.; Jamnuch, S.; Schwartz, C.; Helk, T.; Raj, S.; Mizuno, H.; Mincigrucci, R.; Foglia, L.; Principi, E.; Saykally, R.; Drisdell, W.; Fatehi, S.; et al. (Journal of Physical Chemistry Letters, 2022)
The interaction of intense light with matter gives rise to competing nonlinear responses that can dynamically change material properties. Prominent examples are saturable absorption (SA) and two-photon absorption (TPA), which dynamically increase and decrease the transmission of a sample depending on pulse intensity, respectively. The availability of intense soft X-ray pulses from free-electron lasers (FELs) has led to observations of SA and TPA in separate experiments, leaving open questions about the possible interplay between and relative strength of the two phenomena. Here, we systematically study both phenomena in one experiment by exposing graphite films to soft X-ray FEL pulses of varying intensity. By applying real-time electronic structure calculations, we find that for lower intensities the nonlinear contribution to the absorption is dominated by SA attributed to ground-state depletion; our model suggests that TPA becomes more dominant for larger intensities (>1014 W/cm(2)). Our results demonstrate an approach of general utility for interpreting FEL spectroscopies.
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Self-torqued harmonics and attosecond pulses driven by time-delayed relativistic vortex lasers - Wang, J.; Zepf, M.; Leng, Y.; Li, R.; Rykovanov, S. (Physical Review A, 2022)
Light carrying time-varying orbital angular momentum (OAM) is a recently discovered type of structured electromagnetic field compared with a typical vortex field whose OAM is static. Such so-called self-torqued light is employed for manipulating the fast magnetic, topological, and quantum excitations and increasing its intensity and having access to shorter pulse durations would be of great benefit. Here we theoretically and numerically demonstrate the generation of intense self-torqued harmonics and attosecond pulses in the relativistic regime, driven by two time-delayed relativistic vortex lasers with different OAMs l1 and l2. The OAM of the nth harmonic spans nl1 to nl2, and the OAM of the attosecond pulses changes from l1 to l2. Such intense self-torqued harmonics and attosecond pulses may offer alternative possibilities in ultrafast spectroscopy.
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Signatures of Multiband Effects in High-Harmonic Generation in Monolayer MoS2 br - Yue, L.; Hollinger, R.; Uzundal, C.; Nebgen, B.; Gan, Z.; Najafidehaghani, E.; George, A.; Spielmann, C.; Kartashov, D.; Turchanin, A.; Qiu, D.; Gaarde, M.; et al. (Physical Review Letters, 2022)
High-harmonic generation (HHG) in solids has been touted as a way to probe ultrafast dynamics and crystal symmetries in condensed matter systems. Here, we investigate the polarization properties of highorder harmonics generated in monolayer MoS2, as a function of crystal orientation relative to the midinfrared laser field polarization. At several different laser wavelengths we experimentally observe a prominent angular shift of the parallel-polarized odd harmonics for energies above approximately 3.5 eV, and our calculations indicate that this shift originates in subtle differences in the recombination dipole strengths involving multiple conduction bands. This observation is material specific and is in addition to the angular dependence imposed by the dynamical symmetry properties of the crystal interacting with the laser field, and may pave the way for probing the vectorial character of multiband recombination dipoles.
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Strong-Field Ionization Amplitudes for Atomic Many-Electron Targets - Fritzsche, S.; Boening, B. (Atoms, 2022)
The strong-field approximation (SFA) has been widely applied in the literature to model the ionization of atoms and molecules by intense laser pulses. A recent re-formulation of the SFA in terms of partial waves and spherical tensor operators helped adopt this approach to account for realistic atomic potentials and pulses of different shape and time structure. This re-formulation also enables one to overcome certain limitations of the original SFA formulation with regard to the representation of the initial-bound and final-continuum wave functions of the emitted electrons. We here show within the framework of JAC, the Jena Atomic Calculator, how the direct SFA ionization amplitude can be readily generated and utilized in order to compute above-threshold ionization (ATI) distributions for many-electron targets and laser pulses of given frequency, intensity, polarization, pulse duration and carrier-envelope phase. Examples are shown for selected ATI energy, angular as well as momentum distributions in the strong-field ionization of atomic krypton. We also briefly discuss how this approach can be extended to incorporate rescattering and high-harmonic processes into the SFA amplitudes.
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Towards high photon density for Compton scattering by spectral chirp - Valialshchikov, M. A.; Seipt, D.; Kharin, V. Yu.; Rykovanov, S. G. (Physical Review A, 2022)
Scattering of intense laser pulses on high-energy electron beams allows one to produce a large number of x and gamma rays. For temporally pulsed lasers, the resulting spectra are broadband which severely limits practical applications. One could use linearly chirped laser pulses to compensate for that broadening. We show for laser pulses chirped in the spectral domain that there is the optimal chirp parameter at which the spectra have the brightest peak. Additionally, we use catastrophe theory to analytically find this optimal chirp value.
The results presented in this paper are based on work performed before Feb 24th 2022.
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Characterization of encapsulated graphene layers using extreme ultraviolet coherence tomography - Wiesner, F.; Skruszewicz, S.; R{\"{o}}del, C.; Abel, J.; Reinhard, J.; W{\"{u}}nsche, M.; Nathanael, J.; Gr{\"{u}}newald, M.; H{\"{u}}bner, U.; Paulus, G.; Fuchs, S. (Optics Express, 2022)
Many applications of two-dimensional materials such as graphene require the encapsulation in bulk material. While a variety of methods exist for the structural and functional characterization of uncovered 2D materials, there is a need for methods that image encapsulated 2D materials as well as the surrounding matter. In this work, we use extreme ultraviolet coherence tomography to image graphene flakes buried beneath 200 nm of silicon. We show that we can identify mono-, bi-, and trilayers of graphene and quantify the thickness of the silicon bulk on top by measuring the depth-resolved reflectivity. Furthermore, we estimate the quality of the graphene interface by incorporating a model that includes the interface roughness. These results are verified by atomic force microscopy and prove that extreme ultraviolet coherence tomography is a suitable tool for imaging 2D materials embedded in bulk materials.
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Direct Accessibility of the Fundamental Constants Governing Light-by-Light Scattering - Karbstein, F.; Ullmann, D.; Mosman, E.; Zepf, M. (Physical Review Letters, 2022)
Quantum field theory predicts that the vacuum exhibits a nonlinear response to strong electromagnetic fields. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. We present proof of concept and detailed theoretical analysis of an experimental setup for precision measurements of the quantum vacuum signal generated by the collision of a brilliant x-ray probe with a high-intensity pump laser. The signal features components polarized parallel and perpendicularly to the incident x-ray probe. Our proof-of-concept measurements show that the background can be efficiently suppressed by many orders of magnitude which should not only facilitate a detection of the perpendicularly polarized component of the nonlinear vacuum response, but even make the parallel polarized component experimentally accessible for the first time. Remarkably, the angular separation of the signal from the intense x-ray probe enables precision measurements even in the presence of pump fluctuations and alignment jitter. This provides direct access to the low-energy constants governing light-by-light scattering.
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How the laser beam size conditions the temporal contrast in pulse stretchers of chirped-pulse amplification lasers - R{\"{o}}der, S.; Zobus, Y.; Brabetz, C.; Bagnoud, V. (High Power Laser Science and Engineering, 2022)
In this work, we propose and verify experimentally a model that describes the concomitant influence of the beam size and optical roughness on the temporal contrast of optical pulses passing through a pulse stretcher in chirped-pulse amplification laser systems. We develop an analytical model that is capable of predicting the rising edge caused by the reflection from an optical element in a pulse stretcher, based on the power spectral density of the surface and the spatial beam profile on the surface. In an experimental campaign, we characterize the temporal contrast of a laser pulse that passed through either a folded or an unfolded stretcher design and compare these results with the analytical model. By varying the beam size for both setups, we verify that optical elements in the near- and the far-field act opposed to each with respect to the temporal contrast and that the rising edge caused by a surface benefits from a larger spatial beam size on that surface.
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Accurate Flow Regime Classification and Void Fraction Measurement in Two-Phase Flowmeters Using Frequency-Domain Feature Extraction and Neural Networks - Hosseini, S.; Iliyasu, A.; Akilan, T.; Salama, A.; Eftekhari-Zadeh, E.; Hirota, K. (Separations, 2022)
Two-phase flow is very important in many areas of science, engineering, and industry. Two-phase flow comprising gas and liquid phases is a common occurrence in oil and gas related industries. This study considers three flow regimes, including homogeneous, annular, and stratified regimes ranging from 5-90% of void fractions simulated via the Mont Carlo N-Particle (MCNP) Code. In the proposed model, two NaI detectors were used for recording the emitted photons of a cesium 137 source that pass through the pipe. Following that, fast Fourier transform (FFT), which aims to transfer recorded signals to frequency domain, was adopted. By analyzing signals in the frequency domain, it is possible to extract some hidden features that are not visible in the time domain analysis. Four distinctive features of registered signals, including average value, the amplitude of dominant frequency, standard deviation (STD), and skewness were extracted. These features were compared to each other to determine the best feature that can offer the best separation. Furthermore, artificial neural network (ANN) was utilized to increase the efficiency of two-phase flowmeters. Additionally, two multi-layer perceptron (MLP) neural networks were adopted for classifying the considered regimes and estimating the volumetric percentages. Applying the proposed model, the outlined flow regimes were accurately classified, resulting in volumetric percentages with a low root mean square error (RMSE) of 1.1%.
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Apparent change of the 3C/3D line intensity ratio in neonlike ions - Yang, Z.; He, Z.; Xiong, G.; Yao, K.; Yang, Y.; Wei, B.; Zou, Y.; Wu, Z.; Tian, Z.; Ma, Y.; Wu, C.; Gao, X.; et al. (Optics Express, 2022)
The resonance 3C ([(2p(5))(1/2)3d(3/2)](J=1)->[2p(6)](J=0)) to intercombination 3D ([(2p(5))(3/2) 3d(5/2)](J=1)->[2p(6)](J=0)) line intensity ratio of neonlike ions has been studied. The measured line intensity ratio for neonlike Xe44+ ions shows an apparent change, which is reproduced by the calculations using the relativistic configuration interaction plus many-body perturbation theory. It is clearly elucidated that the change in the 3C/3D line intensity ratio is caused by strong configuration mixing between the upper levels of the 3D and 3F ([(2p(5))(1/2)3s](J=1)->[2p(6)](J=0)) lines. The present measurement allows us to discuss the 3C/3D line intensity ratio for the highest-Z ions hitherto, which suggests that the experiment-theory discrepancy in the 3C/3D line intensity ratio of neonlike ions diminishes with increasing atomic number Z and further trends to vanish at higher-Z ions. Furthermore, the present study provides benefits to better understand configuration mixing effect in the radiative opacity of hot plasmas. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
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Coster-Kronig and super Coster-Kronig transitions from the Xe 4s core-hole state - Hikosaka, Y.; Fritzsche, S. (Physical Chemistry Chemical Physics, 2022)
Coster-Kronig and super Coster-Kronig transitions from the Xe 4s core-hole state are investigated by coincidence detection of all the emitted electrons and product ions. The branching ratios of the transitions are determined by analyzing the coincidence data and comparing them to calculations. Subsequent decay pathways following these first-step Auger decays are also clarified.
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High-intensity laser experiments with highly charged ions in a Penning trap - Ringleb, S.; Kiffer, M.; Stallkamp, N.; Kumar, S.; Hofbrucker, J.; Reich, B.; Arndt, B.; Brenner, G.; Ruiz-Lopez, M.; D{\"{u}}sterer, S.; Vogel, M.; Tiedtke, K.; et al. (Physica Scripta, 2022)
We have conceived and built the HILITE (High-Intensity Laser-Ion Trap Experiment) Penning-trap setup for the production, confinement and preparation of pure ensembles of highly charged ions in a defined quantum state as a target for various high-intensity lasers. This enables a broad suite of laser-ion interaction studies at high photon energies and/or intensities, such as non-linear photo-ionisation studies. The setup has now been used to perform experiments at one such laser facility, namely the FLASH Free-Electron Laser at DESY in Hamburg, Germany. We describe the experimental possibilities of the apparatus, the results of the first measurements and future experiments at other laser facilities.
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Lorentz-force shifts in strong-field ionization with mid-infrared laser fields - Fritzsche, S.; B{\"{o}}ning, B. (Physical Review Research, 2022)
In the past, the ionization of atoms and molecules by strong, mid-infrared (IR) laser fields has attracted recurrent interest. Measurements with different IR pulses have demonstrated the crucial role of the magnetic field on the electron dynamics, classically known as the Lorentz force F-L = q (epsilon + v x B), that acts upon all particles with charge q in motion. These measurements also require the advancement of theory beyond the presently applied methods. In particular, the strong-field approximation (SFA) is typically based on the dipole approximation alone and neglects both the magnetic field and the spatial dependence of the driving electric field. Here we show and discuss that several, if not most, observations from strong-field ionization experiments with mid-IR fields can be quantitatively explained within the framework of SFA, if the Lorentz force is taken into account by nondipole Volkov states in the formalism. The details of such a treatment are analyzed for the (peak) shifts of the polar-angle distribution of above-threshold ionization photoelectrons along the laser propagation, the steering of electron momenta by two not quite collinear laser beams, or the enhanced momentum transfer to photoelectrons in standing-light fields. Moreover, the same formalism promises to explain the generation of high harmonics and other strong-field rescattering phenomena when driven by mid-IR laser fields. All these results show how strong-field processes can be understood on equal footings within the SFA, if one goes beyond the commonly applied dipole approximation.
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Multiple photodetachment of oxygen anions via K-shell excitation and ionization: Direct double-detachment processes and subsequent deexcitation cascades - Schippers, S.; Hamann, A.; Perry-Sassmannshausen, A.; Buhr, T.; M{\"{u}}ller, A.; Martins, M.; Reinwardt, S.; Trinter, F.; Fritzsche, S. (Physical Review A, 2022)
Experimental cross sections for m-fold photodetachment (m = 2-5) of oxygen anions via K-shell excitation and ionization were measured in the photon-energy range of 525-1500 eV using the photon-ion merged-beams technique at a synchrotron light source. The measured cross sections exhibit clear signatures of direct double detachment, including double K-hole creation. The shapes of the double-detachment cross sections as a function of photon energy are in accord with Pattard s [J. Phys. B 35, L207 (2002)] empirical scaling law. We have also followed the complex de-excitation cascades that evolve subsequently to the initial double-detachment events by systematic large-scale cascade calculations. The resulting theoretical product charge-state distributions are in good agreement with the experimental findings.
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Nonlinear pulse compression to 51-W average power GW-class 35-fs pulses at 2-mu m wavelength in a gas-filled multi-pass cell - Gierschke, P.; Grebing, C.; Abdelaal, M.; Lenski, M.; Buldt, J.; Wang, Z.; Heuermann, T.; Mueller, M.; Gebhardt, M.; Rothhardt, J.; Limpert, J. (Optics Letters, 2022)
We report on the generation of GW-class peak power, 35-fs pulses at 2-mu m wavelength with an average power of 51 W at 300-kHz repetition rate. A compact, krypton-filled Herriott-type cavity employing metallic mirrors is used for spectral broadening. This multi-pass compression stage enables the efficient post compression of the pulses emitted by an ultrafast coherently combined thulium-doped fiber laser system. The presented results demonstrate an excellent preservation of the input beam quality in combination with a power transmission as high as 80%. These results show that multi-pass cell based post-compression is an attractive alternative to nonlinear spectral broadening in fibers, which is commonly employed for thulium-doped and other mid-infrared ultra-fast laser systems. Particularly, the average power scalability and the potential to achieve few-cycle pulse durations make this scheme highly attractive. (C) 2022 Optica Publishing Group
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Polarization effects in the total rate of biharmonic omega+3 omega ionization of atoms - Hofbrucker, J.; Ramakrishna, S.; Volotka, A. V.; Fritzsche, S. (Physical Review A, 2022)
The total ionization rate of biharmonic (omega + 3 omega) ionization is studied within the independent particle approximation and the third-order perturbation theory. Particular attention is paid to how the polarization of the biharmonic light field affects the total rate. The ratios of the biharmonic ionization rates for linearly and circularly polarized beams as well as for corotating and counter-rotating elliptically polarized beams are analyzed, and how they depend on the beam parameters, such as photon frequency or phase between omega and 3 omega light beams. We show that the interference of the biharmonic ionization amplitudes determines the dominance of a particular beam polarization over another and that it can be controlled by an appropriate choice of beam parameters. Furthermore, we demonstrate our findings for the ionization of neon L shell electrons.
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QED approach to valence-hole excitation in closed-shell systems - Soguel, R. N.; Volotka, A.; Fritzsche, S. (Physical Review A, 2022)
An ab initio QED approach to treat a valence-hole excitation in closed-shell systems is developed in the framework of the two-time Greens-function method. The derivation considers a redefinition of the vacuum state and its excitation as a valence-hole pair. The proper two-time Greens function, whose spectral representation confirms the poles at valence-hole excitation energies, is proposed. An contour integral formula which connects the energy corrections and the Greens function is also presented. First-order corrections to the valence-hole excitation energy involving self-energy, vacuum polarization, and one-photon-exchange terms are explicitly derived in the redefined vacuum picture. Reduction to the usual vacuum electron propagators is shown, which agrees in the Breit approximation with the many-body perturbation theory expressions for the valence-hole excitation energy.
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Temporal quality of post-compressed pulses at large compression factors - Escoto, E.; Viotti, A.-L.; Ali{{s}}auskas, S.; T{\"{u}}nnermann, H.; Hartl, I.; Heyl, C. (Journal of the Optical Society of America B, 2022)
Post-compression of ultra-short laser pulses via self-phase modulation is routinely employed for the generation of laser pulses with optical bandwidths reaching far beyond the laser gain limitations. Although high compression factors can be routinely achieved, the compressed pulses typically suffer from temporal quality degradation. We numerically and experimentally analyze the deterioration of different measures of temporal quality with increasing compression factor and show how appropriate dispersion management and cascading of the post-compression process can be employed to limit the impact of this effect. The demonstrated saturation of pulse quality degradation at large compression factors puts novel femtosecond laser architectures based on post-compressed picosecond or even nanosecond laser systems in sight.
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Addressing phase-curvature in Fourier ptychography - Aidukas, T.; L{\"{o}}tgering, L.; Harvey, A. (Optics Express, 2022)
In Fourier ptychography, multiple lowresolution images are captured and subsequently combined computationally into a high-resolution, large-field of view micrograph. A theoretical image-formation model based on the assumption of plane-wave illumination from various directions is commonly used, to stitch together the captured information into a high synthetic aperture. The underlying far-field (Fraunhofer) diffraction assumption connects the source, sample, and pupil planes by Fourier transforms. While computationally simple, this assumption neglects phase-curvature due to non-planar illumination from point sources as well as phasecurvature from finite-conjugate microscopes (e.g., using a single-lens for image-formation). We describe a simple, efficient, and accurate extension of Fourier ptychography by embedding the effect of phase-curvature into the underlying forward model. With the improved forward model proposed here, quantitative phase reconstruction is possible even for wide fields-of-views and without the need of image segmentation. Lastly, the proposed method is computationally efficient, requiring only two multiplications: prior and following the reconstruction.
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Angular and polarization properties of the Lyman-alpha(1) line 2p(3/2) -> 1s(1/2) following electron-impact excitation of hydrogenlike ions - Wu, Z. W.; He, Z. M.; Tian, Z. Q.; Dong, C. Z.; Fritzsche, S. (Physical Review A, 2022)
Electron-impact excitation from the ground state to the excited energy level 2p(3/2) of hydrogenlike ions and subsequent Lyman-alpha(1) (2p(3/2) -> 1s(1/2)) radiative decay are investigated using the relativistic distorted-wave method. Special attention is paid to the linear polarization and angular distribution of the Lyman-alpha(1) line and also to the effects of the Breit interaction. To this aim, detailed calculations are performed for hydrogenlike Ti21+, Mo41+, Ba55+, and Au78+ ions. It is found that the presently obtained (partial cross sections and) linear polarization agree excellently with other theoretical and experimental results available for low-Z Ti21+ ions within the experimental uncertainties. Moreover, the Lyman-alpha(1) line is found to be less linearly polarized and less anisotropic due to the contribution of the Breit interaction. Such effects of the Breit interaction behave more prominently for higher-Z ions and higher impact electron energies, respectively. For instance, the Breit interaction qualitatively changes the polarization behavior and angular emission pattern of the Lyman-alpha(1) line from high-Z Au78+ ions at the impact energy of about 4.2 times the corresponding excitation threshold.
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Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time - Schwickert, D.; Ruberti, M.; Kolorenc, P.; Usenko, S.; Przystawik, A.; Baev, K.; Baev, I.; Braune, M.; Bocklage, L.; Czwalinna, M.; Deinert, S.; Duesterer, S.; et al. (Science Advances, 2022)
Here, we use x-rays to create and probe quantum coherence in the photoionized amino acid glycine. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay and by photoelectron emission from sequential double photoionization. Sinusoidal temporal modulation of the detected signal at early times (0 to 25 fs) is observed in both measurements. Advanced ab initio many-electron simulations allow us to explain the first 25 fs of the detected coherent quantum evolution in terms of the electronic coherence. In the kinematically complete x-ray absorption measurement, we monitor its dynamics for a period of 175 fs and observe an evolving modulation that may implicate the coupling of electronic to vibronic coherence at longer time scales. Our experiment provides a direct support for the existence of long-lived electronic coherence in photoionized biomolecules.
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Enhanced Gamma-Ray Attenuation-Based Detection System Using an Artificial Neural Network - Eftekhari-Zadeh, E.; Bensalama, A.; Roshani, G.; Salama, A.; Spielmann, C.; Iliyasu, A. (Photonics, 2022)
Scale deposition is the accumulation of various materials in the walls of transmission lines and unwanted parts in the oil and gas production system. It is a leading moot point in all transmission lines, tanks, and petroleum equipment. Scale deposition leads to drastic detrimental problems, reduced permeability, pressure and production losses, and direct financial losses due to the failure of some equipment. The accumulation of oil and gas leads to clogged pores and obstruction of fluid flow. Considering the passage of a two-phase flow, our study determines the thickness of the scale, and the flow regime is detected with the help of two Multilayer Perceptron (MLP) networks. First, the diagnostic system consisting of a dual-energy source, a steel pipe, and a NaI detector was implemented, using the Monte Carlo N Particle Code (MCNP). Subsequently, the received signals were processed, and properties were extracted using the wavelet transform technique. These features were considered as inputs of an Artificial Neural Network (ANN) model used to determine the type of flow regimes and predict the scale thickness. By accurately classifying the flow regimes and determining the scale inside the pipe, our proposed method provides a platform that could enhance many areas of the oil industry.
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High-power multicore fiber laser systems - Klenke, A.; Jauregui, C.; Steinkopff, A.; Aleshire, C.; Limpert, J. (Progress in Quantum Electronics, 2022)
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