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2021

M. Gebhardt, T. Heuermann, R. Klas, C. Liu, A. Kirsche, M. Lenski, Z. Wang, C. Gaida, J. E. Antonio-Lopez, A. Schulzgen, R. Amezcua-Correa, J. Rothhardt, and J. Limpert
Bright, high-repetition-rate water window soft X-ray source enabled by nonlinear pulse self-compression in an antiresonant hollow-core fibre
Light Sci. Appl., 10 :2021 (February 2021)

Abstract:

Bright, coherent soft X-ray radiation is essential to a variety of applications in fundamental research and life sciences. To date, a high photon flux in this spectral region can only be delivered by synchrotrons, free-electron lasers or high-order harmonic generation sources, which are driven by kHz-class repetition rate lasers with very high peak powers. Here, we establish a novel route toward powerful and easy-to-use SXR sources by presenting a compact experiment in which nonlinear pulse self-compression to the few-cycle regime is combined with phase-matched high-order harmonic generation in a single, helium-filled antiresonant hollow-core fibre. This enables the first 100 kHz-class repetition rate, table-top soft X-ray source that delivers an application-relevant flux of 2.8 x 10(6) photon s(-1) eV(-1) around 300 eV. The fibre integration of temporal pulse self-compression (leading to the formation of the necessary strong-field waveforms) and pressure-controlled phase matching will allow compact, high-repetition-rate laser technology, including commercially available systems, to drive simple and cost-effective, coherent high-flux soft X-ray sources.

A.-L. Calendron, J. Meier, E. Kueny, S. Velten, L. Bocklage, R. Röhlsberger, and F. Kaertner
Bulk, cascaded pulse compression scheme and it s application to spin emitter characterization
Appl. Opt., 60 :912 (February 2021)

Abstract:

The 35-fs-long pulses of a commercial Ti:sapphire amplifier are compressed to similar to 20 fs via self-phase modulation in bulk glass substrates. The cascading of both nonlinear broadening and dispersion compensation stages makes use of the increasing peak power in the successive nonlinear stages. As an application example, the compressed pulses are used for electro-optical sampling of terahertz waves created by optically pumped thin-film spin emitters. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

K. Heeg, A. Kaldun, C. Strohm, C. Ott, R. Subramanian, D. Lentrodt, J. Haber, H.-C. Wille, S. Goerttler, R. Rüffer, C. Keitel, R. Röhlsberger, T. Pfeifer, and J. Evers
Coherent X-ray-optical control of nuclear excitons
Nature, 590 :401 (February 2021)

Abstract:

Coherent control of quantum dynamics is key to a multitude of fundamental studies and applications1. In the visible or longer-wavelength domains, near-resonant light fields have become the primary tool with which to control electron dynamics2. Recently, coherent control in the extreme-ultraviolet range was demonstrated3, with a few-attosecond temporal resolution of the phase control. At hard-X-ray energies (above 5—10 kiloelectronvolts), Mössbauer nuclei feature narrow nuclear resonances due to their recoilless absorption and emission of light, and spectroscopy of these resonances is widely used to study the magnetic, structural and dynamical properties of matter4,5. It has been shown that the power and scope of Mössbauer spectroscopy can be greatly improved using various control techniques6—16. However, coherent control of atomic nuclei using suitably shaped near-resonant X-ray fields remains an open challenge. Here we demonstrate such control, and use the tunable phase between two X-ray pulses to switch the nuclear exciton dynamics between coherent enhanced excitation and coherent enhanced emission. We present a method of shaping single pulses delivered by state-of-the-art X-ray facilities into tunable double pulses, and demonstrate a temporal stability of the phase control on the few-zeptosecond timescale. Our results unlock coherent optical control for nuclei, and pave the way for nuclear Ramsey spectroscopy17 and spin-echo-like techniques, which should not only advance nuclear quantum optics18, but also help to realize X-ray clocks and frequency standards19. In the long term, we envision time-resolved studies of nuclear out-of-equilibrium dynamics, which is a long-standing challenge in Mössbauer science20.

M. Ruijter, V. Petrillo, and M. Zepf
Decreasing the bandwidth of linear and nonlinear Thomson scattering radiation for electron bunches with a finite energy spread
Phys. Rev. ST Accel. Beams, 24 :020702 (February 2021)

Abstract:

Relative narrow bandwidth-high energy radiation can be produced through Thomson scattering, where highly relativistic electrons collide with a laser pulse. The bandwidth of such a source is determined, among others factors, by the bandwidth of the laser pulse and the energy spread of the electrons. Here we investigate how the bandwidth of such a source can be minimized, with a particular emphasis on electron bunches with a correlated energy spread of several percent, that are typical for plasma based accelerator schemes. We show that by introducing a chirp on the laser pulse it is possible to compensate the broadening effect due to the energy spread of the electrons, and obtain the same bandwidth as a quasi-monochromatic plane wave laser pulse colliding with a monoenergetic electron bunch. Ultimately, the bandwidth of a Thomson source is limited by the acceptance angle and the initial transverse momentum of electrons (emittance).

L. Stoyanov, M. Zhekova, A. Stefanov, B. Ivanov, I. Stefanov, G. Paulus, and A. Dreischuh
Generation of long range low-divergent Gauss-Bessel beams by annihilating optical vortices
Opt. Commun., 480 :126510 (February 2021)

Abstract:

Bessel beams are remarkable since they do not diverge. Accordingly, they have numerous applications ranging from precision laser micro-machining to laser particle acceleration. We demonstrate a novel approach for generating long-range Gauss-Bessel beams. A ring-shaped beam is produced by imprinting a vortex with high topological charge in a Gaussian beam. The phase singularities are thereafter removed and the ring-shaped beam focused/Fourier-transformed by a thin lens. This results in a remarkably good realization of a Gauss- Bessel beam. Divergence angles in the microradian range and Gauss-Bessel beam lengths up to 2.5 m behind the focal plane of the lens are demonstrated.

F. Wiesner, M. Wünsche, J. Reinhard, J. Abel, J. Nathanael, S. Skruszewicz, C. Rödel, S. Yulin, A. Gawlik, G. Schmidl, U. Huebner, J. Plentz, G. Paulus, and S. Fuchs
Material-specific imaging of nanolayers using extreme ultraviolet coherence tomography
Optica, 8 :230 (February 2021)

Abstract:

Scientific and technological progress depend substantially on the ability to image on the nanoscale. In order to investigate complex, functional, nanoscopic structures like, e.g., semiconductor devices, multilayer optics, or stacks of 2D materials, the imaging techniques not only have to provide images but should also provide quantitative information. We report the material-specific characterization of nanoscopic buried structures with extreme ultraviolet coherence tomography. The method is demonstrated at a laser-driven broadband extreme ultraviolet radiation source, based on high-harmonic generation. We show that, besides nanoscopic axial resolution, the spectral reflectivity of all layers in a sample can be obtained using algorithmic phase reconstruction. This provides localized, spectroscopic, material-specific information of the sample. The method can be applied in, e.g., semiconductor production, lithographic mask inspection, or quality control of multilayer fabrication. Moreover, it paves the way for the investigation of ultrafast nanoscopic effects at functional buried interfaces. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

S. Schippers, R. Beerwerth, S. Bari, T. Buhr, K. Holste, A. Kilcoyne, A. Perry-Sassmannshausen, R. Phaneuf, S. Reinwardt, D. Savin, K. Schubert, S. Fritzsche, M. Martins, and A. Müller
Near L-edge Single and Multiple Photoionization of Doubly Charged Iron Ions
Astrophys. J., 908 :52 (February 2021)

W. Nörtershäuser, A. Surzhykov, R. Sanchez, B. Botermann, G. Gwinner, G. Huber, S. Karpuk, T. Kühl, C. Novotny, S. Reinhardt, G. Saathoff, T. Stöhlker, and A. Wolf
Polarization-dependent disappearance of a resonance signal: Indication for optical pumping in a storage ring?
Phys. Rev. Accel. Beams, 24 :024701 (February 2021)

Abstract:

We report on laser spectroscopic measurements on Li+ ions in the experimental storage ring ESR at the GSI Helmholtz Centre for Heavy Ion Research. Driving the 2s 3S1(F=3/2)↔2p 3P2(F=5/2)↔2s 3S1(F=5/2) Λ-transition in 7Li+ with two superimposed laser beams it was found that the use of circularly polarized light leads to a disappearance of the resonance structure in the fluorescence signal. This can be explained by optical pumping into a dark state of polarized ions. We present a detailed theoretical analysis of this process that supports the interpretation of optical pumping and demonstrates that the polarization induced by the laser light must then be at least partially maintained during the round trip of the ions in the storage ring. Such polarized ion beams in storage rings will provide opportunities for new experiments, especially on parity violation.

M. Drągowski, M. Adamus, G. Weber, and M. Wlodarczyk
Polarized electron Mott scattering model for the Geant4 Monte Carlo toolkit
Nucl. Instr. Meth. B, 488 :37 (February 2021)

Abstract:

A new method for simulation of polarized electron interactions with matter, based on the Geant4 Monte Carlo toolkit, is presented. The extension consists of a Mott scattering model taking into account the polarization dependence of the cross section, as well as the change of electron polarization in the scattering. The results regarding azimuthal asymmetry in Mott scattering of polarized electron beams off gold and lead targets are compared to available experimental data for energies up to 14 MeV.

A.-L. Viotti, S. Ališauskas, A. Bin Wahid, P. Balla, N. Schirmel, B. Manschwetus, I. Hartl, and C. Heyl
60 fs, 1030nm FEL pump—probe laser based on a multi-pass post-compressed Yb:YAG source
J. Synchrotron Radiat., 28 :36 (January 2021)

Abstract:

This paper reports on nonlinear spectral broadening of 1.1ps pulses in a gas-filled multi-pass cell to generate sub-100fs optical pulses at 1030nm and 515nm at pulse energies of 0.8mJ and 225\textdollar µ \textdollar J, respectively, for pump—probe experiments at the free-electron laser FLASH. Combining a 100kHz Yb:YAG laser with\textasciitilde 180W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump—probe experiments.

B. Böning, P. Abele, W. Paufler, and S. Fritzsche
A strong-field approach with realistic wave functions to the above-threshold ionization of Ba+
J. Phys. B, 54 :025602 (January 2021)

Abstract:

We study the above-threshold ionization of atoms in intense circularly polarized laser pulses. In order to compute photoelectron energy spectra, we apply the strong-field approximation with different models for the initial state wave function. Specifically, we compare the spectra for singly ionized Barium (Ba^+) using hydrogenic wave functions and realistic one-particle wave functions obtained by multiconfiguration Dirac–Hartree–Fock computations, respectively. As a particular example, we discuss the dependence of the photoelectron spectra on the magnetic quantum number m of the initial state and we reproduce the well known m-selectivity in strong-field ionization. Here, we show that the photoelectron spectra exhibit noticeable differences for the two models of the initial state and that the m-selectivity is enhanced when realistic wave functions are used. We conclude that the description of strong-field processes within the strong-field approximation will benefit from a realistic description of the initial atomic state.

B. Marx-Glowna, I. Uschmann, K. Schulze, H. Marschner, H.-C. Wille, K. Schlage, T. Stöhlker, R. Röhlsberger, and G. Paulus
Advanced X-ray polarimeter design for nuclear resonant scattering
J. Synchrotron Radiat., 28 :120 (January 2021)

Abstract:

This work presents the improvements in the design and testing of polarimeters based on channel-cut crystals for nuclear resonant scattering experiments at the 14.4 keV resonance of Fe-57. By using four asymmetric reflections at asymmetry angles of alpha(1) = -28 degrees, alpha(2) = 28 degrees, alpha(3) = -28 degrees and alpha(4) = 28 degrees, the degree of polarization purity could be improved to 2.2 x 10(-9). For users, an advanced polarimeter without beam offset is now available at beamline P01 of the storage ring PETRA III.

A. Seidel, J. Osterhoff, and M. Zepf
Characterizing ultralow emittance electron beams using structured light fields
Phys. Rev. Accel. Beams, 24 :012803 (January 2021)

Abstract:

Novel schemes for generating ultralow emittance electron beams have been developed in past years and promise compact particle sources with excellent beam quality suitable for future high-energy physics experiments and free-electron lasers. Current methods for the characterization of low emittance electron beams such as pepperpot measurements or beam focus scanning are limited in their capability to resolve emittances in the sub 0.1 mm mrad regime. Here we propose a novel, highly sensitive method for the single shot characterization of the beam waist and emittance using interfering laser beams. In this scheme, two laser pulses are focused under an angle creating a gratinglike interference pattern. When the electron beam interacts with the structured laser field, the phase space of the electron beam becomes modulated by the laser ponderomotive force and results in a modulated beam profile after further electron beam phase advance, which allows for the characterization of ultralow emittance beams. 2D PIC simulations show the effectiveness of the technique for normalized emittances in the range of epsilon(n) = 1/20.01; 1] mm mrad.

L. Bocklage, J. Gollwitzer, C. Strohm, C. Adolff, K. Schlage, I. Sergeev, O. Leupold, H.-C. Wille, G. Meier, and R. Röhlsberger
Coherent control of collective nuclear quantum states via transient magnons
Science Advances, 7 :eabc3991 (January 2021)

Abstract:

Ultrafast and precise control of quantum systems at x-ray energies involves photons with oscillation periods below 1 as. Coherent dynamic control of quantum systems at these energies is one of the major challenges in hard x-ray quantum optics. Here, we demonstrate that the phase of a quantum system embedded in a solid can be coherently controlled via a quasi-particle with subattosecond accuracy. In particular, we tune the quantum phase of a collectively excited nuclear state via transient magnons with a precision of 1 zs and a timing stability below 50 ys. These small temporal shifts are monitored interferometrically via quantum beats between different hyperfine-split levels.The experiment demonstrates zeptosecond interferometry and shows that transient quasi-particles enable accurate control of quantum systems embedded in condensed matter environments.

A. T. Schmitt, Y. Joly, K. S. Schulze, B. Marx-Glowna, I. Uschmann, B. Grabiger, H. Bernhardt, R. Lötzsch, A. Juhin, J. Debray, H.-C. Wille, H. Yavaş, G.G. Paulus, and R. Röhlsberger
Disentangling x-ray dichroism and birefringence via high-purity polarimetry
Optica, 8 :56 (January 2021)

Abstract:

High-brilliance synchrotron radiation sources have opened new avenues for x-ray polarization analysis that go far beyond conventional polarimetry in the optical domain. With linear x-ray polarizers in a crossed setting, polarization extinction ratios down to 10⁻¹⁰ can be achieved. This renders the method sensitive to probe the tiniest optical anisotropies that would occur, for example, in strong-field quantum electrodynamics due to vacuum birefringence and dichroism. Here we show that high-purity polarimetry can be employed to reveal electronic anisotropies in condensed matter systems with utmost sensitivity and spectral resolution. Taking CuO and La₂CuO₄ as benchmark systems, we present a full characterization of the polarization changes across the Cu K-absorption edge and their separation into dichroic and birefringent contributions. At diffraction-limited synchrotron radiation sources and x-ray lasers, where polarization extinction ratios of 10⁻¹² can be achieved, our method has the potential to assess birefringence and dichroism of the quantum vacuum in extreme electromagnetic fields.

L. Wollenweber, T. R. Preston, A. Descamps, V. Cerantola, A. Comley, J. H. Eggert, L. B. Fletcher, G. Geloni, D. O. Gericke, S. H. Glenzer, S. Goede, J. Hastings, O. S. Humphries, A. Jenei, O. Karnbach, Z. Konopkova, R. Lötzsch, B. Marx-Glowna, E. E. McBride, D. McGonegle, G. Monaco, B. K. Ofori-Okai, C. A. J. Palmer, C. Plückthun, R. Redmer, C. Strohm, I. Thorpe, T. Tschentscher, I. Uschmann, J. S. Wark, T. G. White, K. Appel, G. Gregori, and U. Zastrau
High-resolution inelastic x-ray scattering at the high energy density scientific instrument at the Free-Electron Laser
Rev. Sci. Instrum., 92 :013101 (January 2021)

Abstract:

We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. An energy resolution of 44 meV is demonstrated for the experimental setup, close to the theoretically achievable minimum resolution. The analyzer crystals and detector are mounted on a curved-rail system, allowing quick and reliable changes in scattering angle without breaking vacuum. The entire setup is designed for operation at 10 Hz, the same repetition rate as the high-power lasers available at the instrument and the fundamental repetition rate of the European XFEL. Among other measurements, it is envisioned that this setup will allow studies of the dynamics of highly transient laser generated states of matter.

R. Hollinger, P. Herrmann, V. Korolev, M. Zapf, V. Shumakova, R. Roeder, I. Uschmann, A. Pugžlys, A. Baltuska, M. Zürch, C. Ronning, C. Spielmann, and D. Kartashov
Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO
Nanomaterials, 11 :4 (January 2021)

Abstract:

The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this work we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3-4 mu m. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.

S. Strnat, V. A. Yerokhin, A. V. Volotka, G. Weber, S. Fritzsche, R. A. Müller, and A. Surzhykov
Polarization studies on Rayleigh scattering of hard x rays by closed-shell atoms
Phys. Rev. A, 103 :012801 (January 2021)

Abstract:

We present a theoretical study on the elastic Rayleigh scattering of x-ray photons by closed-shell atoms. Special attention is paid to the transfer of linear polarization from the incident to the outgoing photons. To study this process, we apply the density-matrix formalism combined with the relativistic perturbation theory. This formalism enables us to find general relations between the Stokes parameters of the incident and scattered photons. By using these expressions, we revisit the recent proposal to use Rayleigh scattering for the analysis of the polarization purity of synchrotron radiation. We show that this analysis can be performed without any need for the theoretically calculated scattering amplitudes, if the linear polarization of the scattered light is measured simultaneously at the azimuthal angles 0 degrees and 45 degrees with respect to the plane of the synchrotron. To illustrate our approach, we present detailed calculations for scattering of 145 keV photons by lead atoms.

S. Panahiyan, and S. Fritzsche
Toward simulation of topological phenomena with one-, two-, and three-dimensional quantum walks
Phys. Rev. A, 103 :012201 (January 2021)

Abstract:

We study the simulation of the topological phases in three subsequent dimensions with quantum walks. We focus mainly on the completion of a table for the protocols of the quantum walk that could simulate different families of the topological phases in one, two, and three dimensions. We also highlight the possible boundary states that can be observed for each protocol in different dimensions and extract the conditions for their emergences. To further enrich the simulation of the topological phenomena, we include step-dependent coins in the evolution operators of the quantum walks. This leads to step dependence of the simulated topological phenomena and their properties which introduces dynamicity as a feature of simulated topological phases and boundary states. This dynamicity provides the step number of the quantum walk as a means to control and engineer the numbers of topological phases and boundary states, their numbers, types, and even occurrences.

K. S. Schulze, R. Lötzsch, R. Rüffer, I. Uschmann, R. Röhlsberger, and G.G. Paulus
X-ray dichroism in polyimide caused by non-resonant scattering
J. Synchrotron Radiat., 28 :176 (January 2021)

Abstract:

Dichroism is one of the most important optical effects in both the visible and the X-ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.

2020

E. Shestaev, S. Haedrich, N. Walther, T. Eidam, A. Klenke, I. Seres, Z. Bengery, P. Jójárt, Z. Várallyay, A. Borzsonyi, and J. Limpert
Carrier-envelope offset stable, coherently combined ytterbium-doped fiber CPA delivering 1 kW of average power
Opt. Lett., 45 :6350 (December 2020)

Abstract:

We present a carrier-envelope offset (CEO) stable ytterbium-doped fiber chirped-pulse amplification system employing the technology of coherent beam combining and delivering more than 1 kW of average power at a pulse repetition rate of 80 MHz. The CEO stability of the system is 220 mrad rms, characterized out-of-loop with an f-to-2f interferometer in a frequency offset range of 10 Hz to 20 MHz. The high-power amplification system boosts the average power of the CEO stable oscillator by five orders of magnitude while increasing the phase noise by only 100 mrad. No evidence of CEO noise deterioration due to coherent beam combining is found. Low-frequency CEO fluctuations at the chirped-pulse amplifier are suppressed by a slow loop feedback. To the best of our knowledge, this is the first demonstration of a coherently combined laser system delivering an outstanding average power and high CEO stability at the same time.

I. Tamer, M. Hornung, L. Lukas, M. Hellwing, S. Keppler, R. Van Hull, J. Hein, M. Zepf, and M.C. Kaluza
Characterization and application of nonlinear plastic materials for post-CPA pulse compression
Opt. Lett., 45 :6575 (December 2020)

Abstract:

We demonstrate the three-fold post-chirped-pulse-amplification (post-CPA) pulse compression of a high peak power laser pulse using ally) diglycol carbonate (CR39), which was selected as the optimal material for near-field self-phase modulation out of a set of various nonlinear plastic materials, each characterized with respect to its nonlinear refractive index and optical transmission. The investigated materials could be applied for further pulse compression at high peak powers, as well as for gain narrowing compensation within millijoule-class amplifiers. The post-CPA pulse compression technique was tested directly after the first CPA stage within the POLARIS laser system, with the compact setup containing a single 1 mm thick plastic sample and a chirped mirror pair, which enabled a substantial shortening of the compressed pulse duration and, hence, a significant increase in the laser peak power without any additional modifications to the existing CPA chain.

R. W. Assmann, M. K. Weikum, T. Akhter, D. Alesini, A. S. Alexandrova, M. P. Anania, N. E. Andreev, I. Andriyash, M. Artioli, A. Aschikhin, T. Audet, A. Bacci, I. F. Barna, S. Bartocci, A. Bayramian, A. Beaton, A. Beck, M. Bellaveglia, A. Beluze, A. Bernhard, A. Biagioni, S. Bielawski, F. G. Bisesto, A. Bonatto, L. Boulton, F. Brandi, R. Brinkmann, F. Briquez, F. Brottier, E. Bründermann, M. Büscher, B. Buonomo, M. H. Bussmann, G. Bussolino, P. Campana, S. Cantarella, K. Cassou, A. Chance, M. Chen, E. Chiadroni, A. Cianchi, F. Cioeta, J. A. Clarke, J. M. Cole, G. Costa, M.-E. Couprie, J. Cowley, M. Croia, B. Cros, P. A. Crump, R. D’Arcy, G. Dattoli, A. Del Dotto, N. Delerue, M. Del Franco, P. Delinikolas, S. De Nicola, J. M. Dias, D. Di Giovenale, M. Diomede, E. Di Pasquale, G. Di Pirro, G. Di Raddo, U. Dorda, A. C. Erlandson, K. Ertel, A. Esposito, F. Falcoz, A. Falone, R. Fedele, A. Ferran Pousa, M. Ferrario, F. Filippi, J. Fils, G. Fiore, R. Fiorito, R. A. Fonseca, G. Franzini, M. Galimberti, A. Gallo, T. C. Galvin, A. Ghaith, A. Ghigo, D. Giove, A. Giribono, L. A. Gizzi, F. J. Grüner, A. F. Habib, C. Haefner, T. Heinemann, A. Helm, B. Hidding, B. J. Holzer, S. M. Hooker, T. Hosokai, M. Hübner, M. Ibison, S. Incremona, A. Irman, F. Iungo, F. J. Jafarinia, O. Jakobsson, D. A. Jaroszynski, S. Jaster-Merz, C. Joshi, M. Kaluza, M. Kando, O. S. Karger, S. Karsch, E. Khazanov, D. Khikhlukha, M. Kirchen, G. Kirwan, C. Kitégi, A. Knetsch, D. Kocon, P. Koester, O. S. Kononenko, G. Korn, I. Kostyukov, K. O. Kruchinin, L. Labate, C. Le Blanc, C. Lechner, P. Lee, W. Leemans, A. Lehrach, X. Li, Y. Li, V. Libov, A. Lifschitz, C. A. Lindstrøm, V. Litvinenko, W. Lu, O. Lundh, A. R. Maier, V. Malka, G. G. Manahan, S. P. D. Mangles, A. Marcelli, B. Marchetti, O. Marcouillé, A. Marocchino, F. Marteau, A. Martinez de la Ossa, J. L. Martins, P. D. Mason, F. Massimo, F. Mathieu, G. Maynard, Z. Mazzotta, S. Mironov, A. Y. Molodozhentsev, S. Morante, A. Mosnier, A. Mostacci, A.-S. Müller, C. D. Murphy, Z. Najmudin, P. A. P. Nghiem, F. Nguyen, P. Niknejadi, A. Nutter, J. Osterhoff, D. Oumbarek Espinos, J.-L. Paillard, D. N. Papadopoulos, B. Patrizi, R. Pattathil, L. Pellegrino, A. Petralia, V. Petrillo, L. Piersanti, M. A. Pocsai, K. Poder, R. Pompili, L. Pribyl, D. Pugacheva, B. A. Reagan, J. Resta-Lopez, R. Ricci, S. Romeo, M. Rossetti Conti, A. R. Rossi, R. Rossmanith, U. Rotundo, E. Roussel, L. Sabbatini, P. Santangelo, G. Sarri, L. Schaper, P. Scherkl, U. Schramm, C. B. Schroeder, J. Scifo, L. Serafini, G. Sharma, Z. M. Sheng, V. Shpakov, C. W. Siders, L. O. Silva, T. Silva, C. Simon, C. Simon-Boisson, U. Sinha, E. Sistrunk, A. Specka, T. M. Spinka, A. Stecchi, A. Stella, F. Stellato, M. J. V. Streeter, A. Sutherland, E. N. Svystun, D. Symes, C. Szwaj, G. E. Tauscher, D. Terzani, G. Toci, P. Tomassini, R. Torres, D. Ullmann, C. Vaccarezza, M. Valléau, M. Vannini, A. Vannozzi, S. Vescovi, J. M. Vieira, F. Villa, C.-G. Wahlström, R. Walczak, P. A. Walker, K. Wang, A. Welsch, C. P. Welsch, S. M. Weng, S. M. Wiggins, J. Wolfenden, G. Xia, M. Yabashi, H. Zhang, Y. Zhao, J. Zhu, and A. Zigler
EuPRAXIA Conceptual Design Report
Eur. Phys. J. Special Topics, 229 :3675 (December 2020)

Abstract:

This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.

M. A. Leutenegger, S. Kuhn, P. Micke, R. Steinbrügge, J. Stierhof, C. Shah, N. Hell, M. Bissinger, M. Hirsch, R. Ballhausen, M. Lang, C. Gräfe, S. Wipf, R. Cumbee, G. L. Betancourt-Martinez, S. Park, V. A. Yerokhin, A. Surzhykov, W. C. Stolte, J. Niskanen, M. Chung, F. S. Porter, T. Stöhlker, T. Pfeifer, J. Wilms, G. V. Brown, J. R. C. Lopez-Urrutia, and S. Bernitt
High-Precision Determination of Oxygen Kα Transition Energy Excludes Incongruent Motion of Interstellar Oxygen
Phys. Rev. Lett., 125 :243001 (December 2020)

Abstract:

We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O2 with 8 meV uncertainty. We reveal a systematic ∼450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.

A. Steinkopff, C. Jauregui, C. Aleshire, A. Klenke, and J. Limpert
Impact of thermo-optical effects in coherently combined multicore fiber amplifiers
Opt. Express, 28 :38093 (December 2020)

Abstract:

In this work we analyze the power scaling potential of amplifying multicore fibers (MCFs) used in coherently combined systems. In particular, in this study we exemplarily consider rod-type MCFs with 2 × 2 up to 10 × 10 ytterbium-doped cores arranged in a squared pattern. We will show that, even though increasing the number of active cores will lead to higher output powers, particular attention has to be paid to arising thermal effects, which potentially degrade the performance of these systems. Additionally, we analyze the influence of the core dimensions on the extractable and combinable output power and pulse energy. This includes a detailed study on the thermal effects that influence the propagating transverse modes and, in turn, the amplification efficiency, the combining efficiency, the onset of nonlinear effect, as well as differences in the optical path lengths between the cores. Considering all these effects under rather extreme conditions, the study predicts that average output powers higher than 10 kW from a single 1 m long ytterbium-doped MCF are feasible and femtosecond pulses with energies higher than 400 mJ can be extracted and efficiently recombined in a filled-aperture scheme.

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