Peer-Review Publications


M. Yeung, B. Dromey, S. Cousens, T. Dzelzainis, D. Kiefer, J. Schreiber, J. Bin, W. Ma, C. Kreuzer, J. Meyer-ter-Vehn, M. Streeter, P. Foster, S. Rykovanov, and M. Zepf
Dependence of Laser-Driven Coherent Synchrotron Emission Efficiency on Pulse Ellipticity and Implications for Polarization Gating
Phys. Rev. Lett., 112 :123902 (March 2014)
The polarization dependence of laser-driven coherent synchrotron emission transmitted through thin foils is investigated experimentally. The harmonic generation process is seen to be almost completely suppressed for circular polarization opening up the possibility of producing isolated attosecond pulses via polarization gating. Particle-in-cell simulations suggest that current laser pulses are capable of generating isolated attosecond pulses with high pulse energies.
B. Aurand, S. Kuschel, O. Jäckel, C. Rödel, H. Zhao, S. Herzer, A. Paz, J. Bierbach, J. Polz, B. Elkin, A. Karmakar, P. Gibbon, M.C. Kaluza, and T. Kühl
Enhanced radiation pressure-assisted acceleration by temporally tuned counter-propagating pulses
Nucl. Instr. Meth. Phys. Res. A, 740 :83 (March 2014)
Within the last decade, laser-ion acceleration has become a field of broad interest. The possibility to generate short proton- or heavy ion bunches with an energy of a few tens of MeV by table-top laser systems could open new opportunities for medical or technical applications. Nevertheless, today's laser-acceleration schemes lead mainly to a temperature-like energy distribution of the accelerated ions, a big disadvantage compared to mono-energetic beams from conventional accelerators. Recent results [1] of laser-ion acceleration using radiation-pressure appear promising to overcome this drawback. In this paper, we demonstrate the influence of a second counter-propagating laser pulse interacting with a nm-thick target, creating a well defined pre-plasma.
D. Gwynne, S. Kar, D. Doria, H. Ahmed, M. Cerchez, J. Fernandez, R. J. Gray, J. S. Green, F. Hanton, D. A. MacLellan, P. McKenna, Z. Najmudin, D. Neely, J. A. Ruiz, A. Schiavi, M. Streeter, M. Swantusch, O. Willi, M. Zepf, and M. Borghesi
Modified Thomson spectrometer design for high energy, multi-species ion sources
Rev. Sci. Instrum., 85 :033304 (March 2014)
A modification to the standard Thomson parabola spectrometer is discussed, which is designed to measure high energy (tens of MeV/nucleon), broad bandwidth spectra of multi-species ions accelerated by intense laser plasma interactions. It is proposed to implement a pair of extended, trapezoidal shaped electric plates, which will not only resolve ion traces at high energies, but will also retain the lower energy part of the spectrum. While a longer (along the axis of the undeflected ion beam direction) electric plate design provides effective charge state separation at the high energy end of the spectrum, the proposed new trapezoidal shape will enable the low energy ions to reach the detector, which would have been clipped or blocked by simply extending the rectangular plates to enhance the electrostatic deflection.
M. Kübel, K. J. Betsch, N. G. Kling, A. S. Alnaser, J. Schmidt, U. Kleineberg, Y. Deng, I. Ben-Itzhak, G.G. Paulus, T. Pfeifer, J. Ullrich, R. Moshammer, M. F. Kling, and B. Bergues
Non-sequential double ionization of Ar: from the single- to the many-cycle regime
New J. Phys., 16 :033008 (March 2014)
The transition from the near-single to the multi-cycle regime in non-sequential double ionization of argon is investigated experimentally. Argon atoms are exposed to intense laser pulses with a center wavelength around 790 nm and the momenta of electrons and ions generated in the double ionization process are measured in coincidence using a reaction microscope. The duration of the near transform-limited pulses is varied from 4 to 30 fs. We observe an abrupt collapse of the cross-shaped two-electron momentum distribution [17] in the few-cycle regime. The transition to longer pulses is further accompanied by a strong increase in the fraction of anti-correlated to correlated electrons.
A. Blinne, and H. Gies
Pair production in rotating electric fields
Phys. Rev. D, 89 :085001 (March 2014)
We explore Schwinger pair production in rotating time-dependent electric fields using the real-time Dirac-Heisenberg-Wigner formalism. We determine the time evolution of the Wigner function as well as asymptotic particle distributions neglecting backreactions on the electric field. Whereas qualitative features can be understood in terms of effective Keldysh parameters, the field rotation leaves characteristic imprints in the momentum distribution that can be interpreted in terms of interference and multiphoton effects. These phenomena may seed characteristic features of QED cascades created in the antinodes of a high-intensity standing wave laser field.
J. Seres, E. Seres, B. Landgraf, B. Ecker, B. Aurand, A. Hoffmann, G. Winkler, S. Namba, T. Kuehl, and C. Spielmann
Parametric amplification of attosecond pulse trains at 11nm
Sci. Rep., 4 :4254 (March 2014)
We report the first experimental demonstration of the parametric amplification of attosecond pulse trains at around 11 nm. The helium amplifier is driven by intense laser pulses and seeded by high-order harmonics pulses generated in a neon gas jet. Our measurements suggest that amplification takes place only if the seed pulse-trains are perfectly synchronized in time with the driving laser field in the amplifier. Varying the delay, we estimate the durations of the individual extreme ultraviolet pulses within the train to be on the order of 0.2 fs. Our results demonstrate that strong-field parametric amplification can be a suitable tool to amplify weak attosecond pulses from non-destructive pump-probe experiments and it is an important step towards designing amplifiers for realization of energetic XUV pulses with sub-femtosecond duration using compact lasers fitting in university laboratories.
V. A. Zaytsev, A. V. Maiorova, V. M. Shabaev, A. V. Volotka, S. Tashenov, G. Plunien, and T. Stöhlker
Parity-nonconservation effect in the dielectronic recombination of polarized electrons with heavy He-like ions
Phys. Rev. A, 89 :032703 (March 2014)
We investigate the parity nonconservation (PNC) effect in the dielectronic recombination of a polarized electron with a heavy He-like ion into doubly excited [(1s2p1/2)_0 nκ]_1/2 and [(1s2s)_0 nκ]_1/2 states of a Li-like ion. We determine the nuclear charge number Z for which these opposite-parity levels are almost crossing and therefore the PNC effect will be significantly enhanced. Calculations are performed for quantum numbers n≥4 and κ=±1.
R. Riedel, A. Stephanides, M. J. Prandolini, B. Gronloh, B. Jungbluth, T. Mans, and F. Tavella
Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers
Opt. Lett., 39 :1422 (March 2014)
Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal.
U. Zastrau, P. Sperling, M. Harmand, A. Becker, T. Bornath, R. Bredow, S. Dziarzhytski, T. Fennel, L. Fletcher, E. Förster, S. Göde, G. Gregori, V. Hilbert, D. Hochhaus, B. Holst, T. Laarmann, H. Lee, T. Ma, J. Mithen, R. Mitzner, C. Murphy, M. Nakatsutsumi, P. Neumayer, A. Przystawik, S. Roling, M. Schulz, B. Siemer, S. Skruszewicz, J. Tiggesbäumker, S. Toleikis, T. Tschentscher, T. White, M. Wöstmann, H. Zacharias, T. Döppner, S. Glenzer, and R. Redmer
Resolving Ultrafast Heating of Dense Cryogenic Hydrogen
Phys. Rev. Lett., 112 :105002 (March 2014)
We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.
S. Busold, A. Almomani, V. Bagnoud, W. Barth, S. Bedacht, A. Blazevic, O. Boine-Frankenheim, C. Brabetz, T. Burris-Mog, T. Cowan, O. Deppert, M. Droba, H. Eickhoff, U. Eisenbarth, K. Harres, G. Hoffmeister, I. Hofmann, O. Jäckel, R. Jäger, M. Joost, S. Kraft, F. Kroll, M. Kaluza, O. Kester, Z. Lecz, T. Merz, F. Nürnberg, H. Al-Omari, A. Orzhekhovskaya, G. Paulus, J. Polz, U. Ratzinger, M. Roth, G. Schaumann, P. Schmidt, U. Schramm, G. Schreiber, D. Schumacher, T. Stöhlker, A. Tauschwitz, W. Vinzenz, F. Wagner, S. Yaramyshev, and B. Zielbauer
Shaping laser accelerated ions for future applications – The LIGHT collaboration
Nucl. Instr. Meth. Phys. Res. A, 740 :94 (March 2014)
Abstract The generation of intense ion beams from high-intensity laser-generated plasmas has been the focus of research for the last decade. In the LIGHT collaboration the expertise of heavy ion accelerator scientists and laser and plasma physicists has been combined to investigate the prospect of merging these ion beams with conventional accelerator technology and exploring the possibilities of future applications. We report about the goals and first results of the LIGHT collaboration to generate, handle and transport laser driven ion beams. This effort constitutes an important step in research for next generation accelerator technologies.
T. Stöhlker, Y. Litvinov, A. Bräuning-Demian, M. Lestinsky, F. Herfurth, R Maier, D. Prasuhn, R. Schuch, and M. Steck
SPARC collaboration: new strategy for storage ring physics at FAIR
Hyperfine Interact., 227 :45 (March 2014)
SPARC collaboration at FAIR pursues the worldwide unique research program by utilizing storage ring and trapping facilities for highly-charged heavy ions. The main focus is laid on the exploration of the physics at strong, ultra-short electromagnetic fields including the fundamental interactions between electrons and heavy nuclei as well as on the experiments at the border between nuclear and atomic physics. Very recently SPARC worked out a realization scheme for experiments with highly-charged heavy-ions at relativistic energies in the High-Energy Storage Ring HESR and at very low-energies at the CRYRING coupled to the present ESR. Both facilities provide unprecedented physics opportunities already at the very early stage of FAIR operation. The installation of CRYRING, dedicated Low-energy Storage Ring (LSR) for FLAIR, may even enable a much earlier realisation of the physics program of FLAIR with slow anti-protons.
M. Klaiber, E. Yakaboylu, C. Müller, H. Bauke, G.G. Paulus, and K. Z. Hatsagortsyan
Spin dynamics in relativistic ionization with highly charged ions in super-strong laser fields
J. Phys. B, 47 :065603 (March 2014)
Spin dynamics and induced spin effects in above-threshold ionization of hydrogenlike highly charged ions in super-strong laser fields are investigated. Spin-resolved ionization rates in the tunnelling regime are calculated by employing two versions of a relativistic Coulomb-corrected strong-field approximation (SFA). An intuitive simpleman model is developed which explains the derived scaling laws for spin flip and spin asymmetry effects. The intuitive model as well as our ab initio numerical simulations support the analytical results for the spin effects obtained in the dressed SFA where the impact of the laser field on the electron spin evolution in the bound state is taken into account. In contrast, the standard SFA is shown to fail in reproducing spin effects in ionization even at a qualitative level. The anticipated spin-effects are expected to be measurable with modern laser techniques combined with an ion storage facility.
A. Herrmann, S. Kuhn, M. Tiegel, C. Russel, J. Körner, D. Klöpfel, J. Hein, and M. Kaluza
Structure and fluorescence properties of ternary aluminosilicate glasses doped with samarium and europium
J. Mater. Chem. C, 2 :4328 (March 2014)
Various ternary aluminosilicate glasses with the molar compositions 20 Al2O3-60 SiO2-20 R2O (R = Li or Na), 20 Al2O3-60 SiO2-20 RO (R = Mg, Ca or Zn) and 23.1 Al2O3-69.2 SiO2-7.7 R2O3 (R = Y or La) doped with 1 [times] 1020 Sm3+ cm-3 or 1 [times] 1020 Eu3+ cm-3 (about 0.2 mol% Sm2O3 or Eu2O3) were prepared. The glasses were studied with respect to their molecular structure, and their thermo-mechanical and fluorescence properties. All glasses show relatively broad fluorescence excitation and only a weak effect of the glass composition on the emission spectra is observed. Although the glasses should be structurally very similar, huge differences are found in the coefficients of thermal expansion and the glass transition temperatures. The fluorescence lifetime increases steadily with decreasing mean atomic weight and decreasing refractive index of the glasses, which may be explained by local field effects. The only exception from this rule is the zinc aluminosilicate glass, which shows a relatively high fluorescence lifetime. The highest fluorescence lifetime is found for the lithium aluminosilicate glass. The lowest coefficients of thermal expansion are found for zinc- and magnesium aluminosilicate glasses. A low coefficient of thermal expansion is a prerequisite for a high thermal shock resistance of the material and hence favorable for high-power laser applications.
S. B. Hansen, J. Colgan, A. Ya. Faenov, J. Abdallah, S. A. Pikuz, I. Yu. Skobelev, E. Wagenaars, N. Booth, O. Culfa, R. J. Dance, G. J. Tallents, R. G. Evans, R. J. Gray, T. Kämpfer, K. L. Lancaster, P. McKenna, A. K. Rossall, K. S. Schulze, I. Uschmann, A. G. Zhidkov, and N. C. Woolsey
Detailed analysis of hollow ions spectra from dense matter pumped by X-ray emission of relativistic laser plasma
Phys. Plasmas, 21 :031213 (February 2014)
X-ray emission from hollow ions offers new diagnostic opportunities for dense, strongly coupled plasma. We present extended modeling of the x-ray emission spectrum reported by Colgan et al. [Phys. Rev. Lett. 110, 125001 (2013)] based on two collisional-radiative codes: the hybrid-structure Spectroscopic Collisional-Radiative Atomic Model (SCRAM) and the mixed-unresolved transition arrays (MUTA) ATOMIC model. We show that both accuracy and completeness in the modeled energy level structure are critical for reliable diagnostics, investigate how emission changes with different treatments of ionization potential depression, and discuss two approaches to handling the extensive structure required for hollow-ion models with many multiply excited configurations.
C. Kohlfürst, H. Gies, and R. Alkofer
Effective mass signatures in multiphoton pair production
Phys. Rev. Lett., 112 :050402 (February 2014)
Electron-positron pair production in oscillating electric fields is investigated in the nonperturbative threshold regime. Accurate numerical solutions of quantum kinetic theory for corresponding observables are presented and analyzed in terms of a proposed model for an effective mass of electrons and positrons acquired within the given strong electric field. Although this effective mass cannot provide an exact description of the collective interaction of a charged particle with the strong field, physical observables are identified which carry direct and sensitive signatures of the effective mass.
M. Kienel, A. Klenke, T. Eidam, S. Hädrich, J. Limpert, and A. Tünnermann
Energy scaling of femtosecond amplifiers using actively controlled divided-pulse amplification
Opt. Lett., 39 :1049 (February 2014)
Divided-pulse amplification is a promising method for the energy scaling of femtosecond laser amplifiers, where pulses are temporally split prior to amplification and coherently recombined afterwards. We present a method that uses an actively stabilized setup with separated stages for splitting and combining. The additional degrees of freedom can be employed to mitigate the limitations originating from saturation of the amplifier that cannot be compensated in passive double-pass configurations using just one common stage for pulse splitting and combining. In a first proof-of-principle experiment, actively controlled divided pulses are applied in a fiber chirped-pulse amplification system resulting in combined and compressed pulses with an energy of 1.25 mJ and a peak power of 2.9 GW.
J. Seres, E. Seres, B. Landgraf, B. Ecker, B. Aurand, T. Kuehl, and C. Spielmann
High-harmonic generation and parametric amplification in the soft X-rays from extended electron trajectories
Sci. Rep., 4 :4234 (February 2014)
We report, for the first time, the generation of high-order harmonics in a spectral range between 200 eV and 1 keV with an unusual spectral property: only every 4th (4i + 1, i∈ℵ) harmonic line appears, whereas the usual high-harmonic spectra consist of every odd (2i + 1) harmonic. We attribute this unique property to the quantum path interference of two extended electron trajectories that experience multiple re-scattering. In the well-established theory, electrons emitted via tunnel ionisation are accelerated by a laser field, return to the ion and recombine. The acceleration typically lasts for less than one optical cycle, and the electrons radiate in the extreme ultraviolet range at recombination. In contrast, for extended trajectories, electrons are accelerated over two or more optical cycles. Here, we demonstrate that two sets of trajectories dominate and provide substantial contributions to the generated soft X-ray radiation because they fulfil the resonance condition for X-ray parametric amplification.
Z. W. Wu, A. Surzhykov, and S. Fritzsche
Hyperfine-induced modifications to the angular distribution of the Kα1x-ray emission
Phys. Rev. A, 89 :022513 (February 2014)
The angular distribution of the Kα_1 (1s2p_3/2^1,3P_1,2→1s^21S_0) x-ray emission following the radiative electron capture into initially hydrogenlike ions with nonzero nuclear spin has been studied within the density matrix theory and the multiconfiguration Dirac-Fock method. Emphasis is placed especially upon the hyperfine interaction and how this interaction of the magnetic moment of the nucleus with those of the electrons affects the angular properties of the Kα_1 radiation. Calculations were performed for selected isotopes of heliumlike Sn48+, Xe52+, and Tl79+ ions. A quite sizable contribution of the hyperfine interaction upon the Kα_1 angular emission is found for isotopes with nuclear spin I = 1/2, while its effect is suppressed for (most) isotopes with nuclear spin I > 1/2. We therefore suggest that accurate measurements of the Kα_1 angular distribution at ion storage rings can be utilized as a tool for determining the nuclear parameters of rare stable and radioactive isotopes with I ≥ 1/2.
P. Hansinger, G. Maleshkov, N. Gorunski, N. Dimitrov, A. Dreischuh, and G.G. Paulus
Interaction between one-dimensional dark spatial solitons and semi-infinite dark stripes
Opt. Commun., 313 :106 (February 2014)
In this work we numerically study the evolution and interaction of one-dimensional (1-D) dark spatial solitons and semi-infinite dark stripes (SIDSs) in a local self-defocusing Kerr nonlinear medium. The experimental results in the linear regime of propagation confirm that the SIDS bending and fusion with the infinite 1-D dark beam modeled for negative nonlinearity is due to the opposite phase semi-helicities of SID beam ends. Results for several interaction scenaria show that bending ends of the semi-infinite dark stripes splice to the 1-D dark beam to form structures resembling waveguide couplers/branchers. Well pronounced modulational stability of 1-D dark spatial solitons under strong symmetric background beam modulation from decaying SIDSs is predicted.
D. Seipt, and B. Kämpfer
Laser-assisted Compton scattering of x-ray photons
Phys. Rev. A, 89 :023433 (February 2014)
The Compton scattering of x-ray photons, assisted by a short intense optical laser pulse, is discussed. The differential scattering cross section reveals the interesting feature that the main Klein-Nishina line is accompanied by a series of side lines forming a broad plateau where up to O(10^(3)) laser photons participate simultaneously in a single scattering event. An analytic formula for the width of the plateau is given. Due to the nonlinear mixing of x-ray and laser photons a frequency-dependent rotation of the polarization of the final-state x-ray photons relative to the scattering plane emerges. A consistent description of the scattering process with short laser pulses requires to work with x-ray pulses. An experimental investigation can be accomplished, e.g., at LCLS or the European XFEL, in the near future.
X. Xie, S. Roither, M. Schöffler, H. Xu, S. Bubin, E. Lötstedt, S. Erattuphuza, A. Iwasaki, D. Kartashov, K. Varga, G.G. Paulus, A. Baltuska, K. Yamanouchi, and M. Kitzler
Role of proton dynamics in efficient photoionization of hydrocarbon molecules
Phys. Rev. A, 89 :023429 (February 2014)
We experimentally investigate the ionization mechanism behind the formation of remarkably high charge states observed in the laser-pulse-induced fragmentation of different hydrocarbon molecules by Roither et al. [Phys. Rev. Lett. 106, 163001 (2011)], who suggested enhanced ionization occurring at multiple C-H bonds as the underlying ionization mechanism. Using multiparticle coincidence momentum imaging we measure the yield of multiply charged fragmenting ethylene and acetylene molecules at several intensities and pulse durations ranging from the few-cycle regime to 25 fs. We observe, at constant intensity, a strong increase of the proton energy with increasing laser pulse duration. It is shown that this is caused by a strong increase in the yield of highly charged parent molecular ions with pulse duration. Based on experimental evidence we explain this increase by the necessary population of precursor states in the parent ion that feature fast C-H stretch dynamics to the critical internuclear distance, where efficient ionization via enhanced ionization takes place. For increasing pulse duration these precursor ionic states are more efficiently populated, which leads in turn to a higher enhanced-ionization probability for longer pulses. Our work provides experimental evidence for the existence of a multiple-bond version of enhanced ionization in polyatomic molecules.
S. Fritzsche
The Feynman tools for quantum information processing: Design and implementation
Comput. Phys. Commun., 185 :1697 (February 2014)
The Feynman tools have been re-designed with the goal to establish and implement a high-level (computer) language that is capable to deal with the physics of finite, n -qubit systems, from frequently required computations to mathematically advanced tasks in quantum information processing. In particular, emphasis has been placed to introduce a small but powerful set of keystring-driven commands in order to support both, symbolic and numerical computations. Though the current design is implemented again within the framework of Maple, it is general and flexible enough to be utilized and combined with other languages and computational environments. The present implementation facilitates a large number of computational tasks, including the definition, manipulation and parametrization of quantum states, the evaluation of quantum measures and quantum operations, the evolution of quantum noise in discrete models, quantum measurements and state estimation, and several others. The design is based on a few high-level commands, with a syntax close to the mathematical notation and its use in the literature, and which can be generalized quite readily in order to solve computational tasks at even higher degree of complexity. In this work, I present and discuss the (re-design of the) Feynman tools and make major parts of the code available for public use. Moreover, a few selected examples are shown and demonstrate possible application of this toolbox. The Feynman tools are provided as Maple library and can hence be used on all platforms on which this computer-algebra system is accessible.
B. Aurand, B. Elkin, L.-O. Heim, B. Lommel, B. Kindler, M. Tomut, C. Rödel, S. Kuschel, O. Jäckel, and T. Kühl
Ultra-thin polymer foils for laser-ion acceleration
J. Radioanal. Nucl. Chem., 299 :965 (February 2014)
We report on the development of new materials for laser-ion acceleration applicable for the advanced mechanism of radiation-pressure-acceleration. These targets are ultra-thin with thicknesses of just a few nm. For several years, diamond-like carbon foils in this thickness range can be produced. An alternative material containing more than one ion-species has the potential to further improve the acceleration mechanism. The fabrication and characterization of self-supporting polymer-based targets will be described in this paper. Furthermore, we show the significant influence on a radiation-pressure induced acceleration process by experimental data.
M. Huttula, S.-M. Huttula, S. Fritzsche, P. Lablanquie, F. Penent, J. Palaudoux, and L. Andric
Core-valence double photoionization of atomic mercury
Phys. Rev. A, 89 :013411 (January 2014)
Multielectron coincidence spectroscopy has been used to study core 4f valence 5d, 6s double photoionization of atomic mercury. Multiconfiguration Dirac–Fock calculations were performed to calculate the energies and to estimate the single-photon intensities of the 4f^13(5d^96s^2 + 5d^106s^1) double-ionized states of atomic mercury. Reasonable agreement between the measured and simulated spectra is found if the relaxation effects of the bound-state density is taken into account in the computation of the photoionization amplitudes.
M. J. Prandolini, R. Riedel, M. Schulz, A. Hage, H. Höppner, and F. Tavella
Design considerations for a high power, ultrabroadband optical parametricchirped-pulse amplifier
Opt. Express, 22 :1594 (January 2014)
A conceptual design of a high power, ultrabroadband optical parametric chirped-pulse amplifier(OPCPA) was carried out comparing nonlinear crystals (LBO and BBO) for 810 nm centered, sub-7.0 fspulses with energies above 1 mJ. These amplifiers are only possible with a parallel development ofkilowatt-level OPCPA-pump amplifiers. It is therefore important to know good strategies to use theavailable OPCPA-pump energy efficiently. Numerical simulations, including self- and cross-phasemodulation, were used to investigate the critical parameters to achieve sufficient spectral andspatial quality. At high output powers, thermal absorption in the nonlinear crystals starts todegrade the output beam quality. Strategies to minimize thermal effects and limits to the maximumaverage power are discussed.