Peer-Review Publications

2019

A. Steinkopff, C. Jauregui, F. Stutzki, J. Nold, C. Hupel, N. Haarlammert, J. Bierlich, A. Tünnermann, and J. Limpert
Transverse single-mode operation in a passive large pitch fiber with more than 200  µm mode-field diameter
Opt. Lett., 44 :650 (February 2019)
Abstract:
In this Letter, we present, to the best of our knowledge, the largest effective single-mode fiber reported to date. The employed waveguide is a passive large pitch fiber (LPF), which shows the core area scaling potential of such a fiber structure. In particular, we achieved stable single-transverse mode transmission at a wavelength of 1.03 µm through a straight passive LPF with a pitch of 140 µm, resulting in a measured mode-field diameter of 205 µm.
G. Tadesse, W. Eschen, R. Klas, M. Tschernajew, T. Frederik, M. Steinert, M. Zilk, V. Schuster, M. Zürch, T. Pertsch, C. Spielmann, J. Limpert, and J. Rothhardt
Wavelength-scale ptychographic coherent diffractive imaging using a high-order harmonic source
Sci. Rep., 9 :1735 (February 2019)
Abstract:
Ptychography enables coherent diffractive imaging (CDI) of extended samples by raster scanning across the illuminating XUV/X-ray beam, thereby generalizing the unique advantages of CDI techniques. Table- top realizations of this method are urgently needed for many applications in sciences and industry. Previously, it was only possible to image features much larger than the illuminating wavelength with table-top ptychography although knife-edge tests suggested sub-wavelength resolution. However, most real-world imaging applications require resolving of the smallest and closely-spaced features of a sample in an extended field of view. In this work, resolving features as small as 2.5 łambda (45 nm) using a table-top ptychography setup is demonstrated by employing a high-order harmonic XUV source with record-high photon flux. For the first time, a Rayleigh-type criterion is used as a direct and unambiguous resolution metric for high-resolution table-top setup. This reliably qualifies this imaging system for real-world applications e.g. in biological sciences, material sciences, imaging integrated circuits and semiconductor mask inspection.
S. Panahiyan, S. Hendi, and N. Riazi
AdS4 dyonic black holes in gravity's rainbow
Nucl. Instr. Meth. Phys. Res. B, 938 :388 (January 2019)
Abstract:
In this paper, we investigate thermodynamical structure of dyonic black holes in the presence of gravity's rainbow. We confirm that for super magnetized and highly pressurized scenarios, the number of black holes' phases is reduced to a single phase. In addition, due to specific coupling of rainbow functions, it is possible to track the effects of temporal and spatial parts of our setup on thermodynamical quantities/behaviors including equilibrium point, existence of multiple phases, possible phase transitions and conditions for having a uniform stable structure.
M. Durante, P. Indelicato, B. Jonson, V. Koch, K. Langanke, U.-G. Meißner, E. Nappi, T. Nilsson, T. Stöhlker, E. Widmann, and M. Wiescher
All the fun of the FAIR: fundamental physics at the facility for antiproton and ion research
Phys. Scripta, 94 :033001 (January 2019)
Abstract:
The Facility for Antiproton and Ion Research (FAIR) will be the accelerator-based flagship research facility in many basic sciences and their applications in Europe for the coming decades. FAIR will open up unprecedented research opportunities in hadron and nuclear physics, in atomic physics and nuclear astrophysics as well as in applied sciences like materials research, plasma physics and radiation biophysics with applications towards novel medical treatments and space science. FAIR is currently under construction as an international facility at the campus of the GSI Helmholtzzentrum for Heavy-Ion Research in Darmstadt, Germany. While the full science potential of FAIR can only be harvested once the new suite of accelerators and storage rings is completed and operational, some of the experimental detectors and instrumentation are already available and will be used starting in summer 2018 in a dedicated research program at GSI, exploiting also the significantly upgraded GSI accelerator chain. The current manuscript summarizes how FAIR will advance our knowledge in various research fields ranging from a deeper understanding of the fundamental interactions and symmetries in nature to a better understanding of the evolution of the Universe and the objects within.
A. Blinne, H. Gies, F. Karbstein, C. Kohlfürst, and M. Zepf
All-optical signatures of quantum vacuum nonlinearities in generic laser fields
Phys. Rev. D, 99 :016006 (January 2019)
Abstract:
All-optical experiments at the high-intensity frontier offer a promising route to unprecedented precision tests of quantum electrodynamics in strong macroscopic electromagnetic fields. So far, most theoretical studies of all-optical signatures of quantum vacuum nonlinearity are based on simplifying approximations of the beam profiles and pulse shapes of the driving laser fields. Since precision tests require accurate quantitative theoretical predictions, we introduce an efficient numerical tool facilitating the quantitative theoretical study of all-optical signatures of quantum vacuum nonlinearity in generic laser fields. Our approach is based on the vacuum emission picture, and makes use of the fact that the dynamics of the driving laser fields are to an excellent approximation governed by classical Maxwell theory in vacuum. In combination with a Maxwell solver, which self-consistently propagates any given laser field configuration, this allows for accurate theoretical predictions of photonic signatures of vacuum nonlinearity in high-intensity laser experiments from first principles. We employ our method to simulate photonic signatures of quantum vacuum nonlinearity in laser pulse collisions involving a few-cycle pulse, and show that the angular and spectral distributions of the emitted signal photons deviate from those of the driving laser beams.
N. A. Tahir, A. Shutov, A. R. Piriz, P. Neumayer, I. V. Lomonosov, V. Bagnoud, and S. A. Piriz
Application of intense ion beams to planetary physics research at the Facility for Antiprotons and Ion Research facility
Contrib. Plasm. Phys., 59 :e2018001 (January 2019)
Abstract:
This paper presents detailed 2D hydrodynamic simulations of implosion of a multi‐layered cylindrical target that is driven by an intense uranium beam. The target is comprised of a thick, high‐Z, high‐ρ cylindrical shell that encloses a sample material (Fe in the present case). Two options have been used for the focal spot geometry: an annular form and a circular form. The purpose of this work is to show that an intense heavy‐ion beam can induce the extreme physical conditions in the sample material similar to those that exist in the planetary cores. In this study, we use parameters of the beam that will be generated at the Facility for Antiprotons and Ion Research (FAIR), Darmstadt, in a few years' time. Production of these high‐energy‐density (HED) samples will allow us to study planetary physics in the laboratory. It is to be noted that planetary physics research is an important part of the FAIR HED physics program. A dedicated experiment named LAboratory PLAnetary Sciences (LAPLAS) has been proposed for this purpose. These simulations show that in such experiments an Fe sample can be imploded to the Earth's core conditions and to those in more massive rocky planets called Super‐Earths. Similarly, implosion of hydrogen and water samples will generate the core conditions of solar and extrasolar hydrogen‐rich gas giants and water‐rich icy planets, respectively. The LAPLAS experiments will thus provide very valuable information on the equation of state and transport properties of matter under extreme physical conditions, which will help scientists understand the structure and evolution of the planets in our solar system as well as of the extrasolar planets.
L. Schmidl, G. Schmidl, A. Gawlik, J. Dellith, U. Hübner, V. Tympel, F. Schmidl, J. Plentz, C. Geis, and H. Haselmann
Combining super-resolution microscopy with neuronal network recording using magnesium fluoride thin films as cover layer for multi-electrode array technology
Sci. Rep., 9 :16110 ( 2019)
Abstract:
We present an approach for fabrication of reproducible, chemically and mechanically robust functionalized layers based on MgF₂ thin films on thin glass substrates. These show great advantages for use in super-resolution microscopy as well as for multi-electrode-array fabrication and are especially suited for combination of these techniques. The transparency of the coated substrates with the low refractive index material is adjustable by the layer thickness and can be increased above 92%. Due to the hydrophobic and lipophilic properties of the thin crystalline MgF₂ layers, the temporal stable adhesion needed for fixation of thin tissue, e.g. cryogenic brain slices is given. This has been tested using localization-based super-resolution microscopy with currently highest spatial resolution in light microscopy. We demonstrated that direct stochastic optical reconstruction microscopy revealed in reliable imaging of structures of central synapses by use of double immunostaining of post- (homer1 and GluA2) and presynaptic (bassoon) marker structure in a 10 µm brain slice without additional fixing of the slices. Due to the proven additional electrical insulating effect of MgF2 layers, surfaces of multi-electrode-arrays were coated with this material and tested by voltage-current-measurements. MgF₂ coated multi-electrode-arrays can be used as a functionalized microscope cover slip for combination with live-cell super-resolution microscopy.
S. Salman, Y. Ma, K. Gürel, S. Schilt, C. Li, P. Pfäfflein, C. Mahnke, J. Fellinger, S. Droste, A. Mayer, O. Heckl, T. Südmeyer, C. Heyl, and I. Hartl
Comparison of two low-noise CEP stabilization methods for an environmentally stable Yb: fiber oscillator
Advanced Solid State Lasers ( 2019)
DOI
V. Zakosarenko, M. Schmelz, T. Schönau, S. Anders, J. Kunert, V. Tympel, R. Neubert, F. Schmidl, P. Seidel, T. Stöhlker, D. Haider, M. Schwickert, T. Sieber, and R. Stolz
Coreless SQUID-based cryogenic current comparator for non-destructive intensity diagnostics of charged particle beams
Supercond. Sci. Technol., 32 :014002 (January 2019)
Abstract:
We report on a novel concept and prototype development of a coreless SQUID-based charged-particle beam monitor as a non-destructive diagnostic tool for accelerator facilities. Omitting the typically used pickup coil with a high magnetic permeability core leads to a significant improvement in low-frequency noise performance. Moreover, a revised shielding geometry allows for very compact and rather lightweight device designs. Based on highly sensitive SQUIDs featuring sub-micron cross-type Josephson tunnel junctions, our prototype device exhibits a current sensitivity of about 6 pA Hz(-1/2) in the white noise region. Together with a measured shielding factor of about 135 dB this opens up the way for its widespread use in modern accelerator facilities.
A. Blinne, S. Kuschel, S. Tietze, and M. Zepf
Efficient retrieval of phase information from real-valued electromagnetic field data
J. Comput. Phys. X, 1 :100019 (January 2019)
Abstract:
While analytic calculations may give access to complex-valued electromagnetic field data which allow trivial access to envelope and phase information, the majority of numeric codes uses a real-valued representation. This typically increases the performance and reduces the memory footprint, albeit at a price: In the real-valued case it is much more difficult to extract envelope and phase information, even more so if counter propagating waves are spatially superposed. A novel method for the analysis of real-valued electromagnetic field data is presented in this paper. We show that, by combining the real-valued electric and magnetic field at a single point in time, we can directly reconstruct the full information of the electromagnetic fields in the form of complex-valued spectral coefficients (k→-space) at a low computational cost of only three Fourier transforms. The method allows for counter propagating plane waves to be accurately distinguished as well as their complex spectral coefficients, i.e. spectral amplitudes and spectral phase to be calculated. From these amplitudes, the complex-valued electromagnetic fields and also the complex-valued vector potential can be calculated from which information about spatiotemporal phase and amplitude is readily available. Additionally, the complex fields allow for efficient vacuum propagation allowing to calculate far field data or boundary input data from near field data. An implementation of the new method is available as part of PostPic1, a data analysis toolkit written in the Python programming language.
B. Panah, S. Panahiyan, and S. Hendi
Entropy spectrum of charged BTZ black holes in massive gravity's rainbow
Progr. Theor. Exp. Phys., 2019 :013E02 (January 2019)
Abstract:
Regarding the significant interests in massive gravity and combining it with gravity's rainbow and also BTZ black holes, we apply the formalism introduced by Jiang and Han in order to investigate the quantization of the entropy of black holes. We show that the entropy of BTZ black holes in massive gravity's rainbow is quantized with equally spaced spectra and it depends on the black holes' properties including massive parameters, electrical charge, the cosmological constant, and also rainbow functions. In addition, we show that quantization of the entropy results in the appearance of novel properties for this quantity, such as the existence of divergences, non-zero entropy in a vanishing horizon radius, and the possibility of tracing out the effects of the black holes' properties. Such properties are absent in the non-quantized version of the black hole entropy. Furthermore, we investigate the effects of quantization on the thermodynamical behavior of the solutions. We confirm that due to quantization, novel phase transition points are introduced and stable solutions are limited to only de Sitter black holes (anti-de Sitter and asymptotically flat solutions are unstable).
D. Jahn, D. Schumacher, C. Brabetz, F. Kroll, F. E. Brack, J. Ding, R. Leonhardt, I. Semmler, A. Blazevic, U. Schramm, and M. Roth
Focusing of multi-MeV, subnanosecond proton bunches from a laser-driven source
Phys. Rev. Accel. Beams, 22 :011301 (January 2019)
Abstract:
We report on our latest transverse focusing results of subnanosecond proton bunches achieved with a laser-driven multi-MeV ion beamline. In the frame of the LIGHT collaboration, a target normal sheath acceleration (TNSA) source based 6 m long beamline was installed. In the past years, the laser-driven proton beam was transported and shaped by this beamline. The particle beam is collimated with a pulsed high-field solenoid and rotated in longitudinal phase space with a radio-frequency cavity which leads to an energy compression with an energy spread of (2.7 +/- 1.7)% (Delta E/E-0 at FWHM) or a time compression to the subnanosecond regime. Highest peak intensities in the subnanosecond regime open up an interesting field for several applications, e.g., proton imaging, as injectors in conventional accelerators or precise stopping power measurements in a plasma. We report on achieving highest peak intensities using an installed second solenoid as a final focusing system in our beamline to achieve small focal spot sizes. We measured a focal spot size of 1.1 x 1.2 mm leading to 5.8 x 10(19) protons per s cm(2) at a central energy bin of (9.55 +/- 0.25) MeV, which can be combined with a bunch duration below 500 ps at FWHM.
F. Wiesner, S. Fuchs, M. Wünsche, J. Nathanael, J. Abel, J. Reinhard, S. Skruszewicz, C. Rödel, A. Gawlik, G. Schmidl, and . others
Label-free quantitative material sensitive tomography with extreme ultraviolet light
Digital Holography and Three-Dimensional Imaging ( 2019)
DOI
W. J. Ma, I. Kim, J. Q. Yu, I. Choi, P. K. Singh, H. Lee, J. Sung, S. Lee, C. Lin, Q. Liao, J. G. Zhu, H. Y. Lu, B. Liu, H. Y. Wang, R. F. Xu, X. T. He, J. E. Chen, M. Zepf, J. Schreiber, X. Q. Yan, and C. Nam
Laser Acceleration of Highly Energetic Carbon Ions Using a Double-Layer Target Composed of Slightly Underdense Plasma and Ultrathin Foil
Phys. Rev. Lett., 122 :014803 (January 2019)
Abstract:
We report the experimental generation of highly energetic carbon ions up to 48 MeV per nucleon by shooting double-layer targets composed of well-controlled slightly underdense plasma and ultrathin foils with ultraintense femtosecond laser pulses. Particle-in-cell simulations reveal that carbon ions are ejected from the ultrathin foils due to radiation pressure and then accelerated in an enhanced sheath field established by the superponderomotive electron flow. Such a cascaded acceleration is especially suited for heavy ion acceleration with femtosecond laser pulses. The breakthrough of heavy ion energy up to many tens of MeV/u at a high repetition rate would be able to trigger significant advances in nuclear physics, high energy density physics, and medical physics.
T. Helk, M. Zürch, and C. Spielmann
Perspective: Towards single shot time-resolved microscopy using short wavelength table-top light sources
Struct. Dyn., 6 :010902 (January 2019)
Abstract:
Time-resolved imaging allows revealing the interaction mechanisms in the microcosm of both inorganic and biological objects. While X-ray microscopy has proven its advantages for resolving objects beyond what can be achieved using optical microscopes, dynamic studies using full-field imaging at the nanometer scale are still in their infancy. In this perspective, we present the current state of the art techniques for full-field imaging in the extreme-ultraviolet- and soft X-ray-regime which are suitable for single exposure applications as they are paramount for studying dynamics in nanoscale systems. We evaluate the performance of currently available table-top sources, with special emphasis on applications, photon flux, and coherence. Examples for applications of single shot imaging in physics, biology, and industrial applications are discussed.
A. Wallner, M. Bichler, L. Coquard, I. Dillmann, O. Forstner, R. Golser, M. Heil, F. Käppeler, W. Kutschera, C. Lederer-Woods, M. Martschini, A. Mengoni, S. Merchel, L. Michlmayr, A. Priller, P. Steier, and M. Wiescher
Stellar and thermal neutron capture cross section of ⁹Be
Phys. Rev. C, 99 :015804 (January 2019)
Abstract:
The neutron capture cross section of 9Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasistellar neutron spectrum of kT=25 keV and for a spectrum at En=473±53 keV. Despite the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4±0.6 and 8.4±1.0μb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian-averaged cross sections at thermal energies between kT=5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of σth=8.31±0.52 mb.
S. Fuchs, M. Wünsche, J. Nathanael, J. Abel, J. Reinhard, F. Wiesner, S. Skruszewicz, C. Rödel, and G. Paulus
XUV coherence tomography with nanoscale resolution using one-dimensional phase retrieval
Digital Holography and Three-Dimensional Imaging ( 2019)
DOI

2018

L. Obst-Huebl, T. Ziegler, F.-E. Brack, J. Branco, M. Bussmann, T. E. Cowan, C. B. Curry, F. Fiuza, M. Garten, M. Gauthier, S. Göde, S. H. Glenzer, A. Huebl, A. Irman, J. B. Kim, T. Kluge, S. D. Kraft, F. Kroll, J. Metzkes-Ng, R. Pausch, I. Prencipe, M. Rehwald, C. Rödel, H.-P. Schlenvoigt, U. Schramm, and K. Zeil
All-optical structuring of laser-driven proton beam profiles
Nat. Commun., 9 :5292 (December 2018)
Abstract:
Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.
D. Wu, W. Yu, Y. Zhao, S. Fritzsche, and X. He
Characteristics of X/γ-ray radiations by intense laser interactions with high-Z solids: The role of bremsstrahlung and radiation reactions
Matt. Rad. Extrem., 3 :293 (December 2018)
Abstract:
In this work, characteristics of X/γ-ray radiations by intense laser interactions with high-Z solids are investigated by means of a newly developed particle-in-cell (PIC) simulation code. The PIC code takes advantage of the recently developed ionization and collision dynamics models, which make it possible to model different types of materials based on their intrinsic atomic properties. Within the simulations, both bremsstrahlung and nonlinear Compton scatterings have been included. Different target materials and laser intensities are considered for studying the parameter-dependent features of X/γ-ray radiations. The relative strength and angular distributions of X/γ ray productions from bremsstrahlung and nonlinear Compton scatterings are compared to each other. The threshold under which the nonlinear Compton scatterings become dominant over bremsstrahlung is also outlined.
F. Karbstein, M. Wagner, and M. Weber
Determination of ΛMSbar (nf=2) and analytic parametrization of the static quark-antiquark potential
Phys. Rev. D, 98 :114506 (December 2018)
Abstract:
While lattice QCD allows for reliable results at small momentum transfers (large quark separations), perturbative QCD is restricted to large momentum transfers (small quark separations). The latter is determined up to a reference momentum scale Λ, which is to be provided from outside, e.g., from experiment or lattice QCD simulations. In this article, we extract ΛMSbar for QCD with nf=2 dynamical quark flavors by matching the perturbative static quark-antiquark potential in momentum space to lattice results in the intermediate momentum regime, where both approaches are expected to be applicable. In a second step, we combine the lattice and the perturbative results to provide a complete analytic parametrization of the static quark-antiquark potential in position space up to the string breaking scale. As an exemplary phenomenological application of our all-distances potential, we compute the bottomonium spectrum in the static limit.
Y.-G. Jeong, R. Piccoli, D. Ferachou, V. Cardin, M. Chini, S. Hädrich, J. Limpert, R. Morandotti, F. Légaré, B. Schmidt, and L. Razzari
Direct compression of 170-fs 50-cycle pulses down to 1.5 cycles with 70% transmission
Sci. Rep., 8 :11794 (December 2018)
Abstract:
We present a straightforward route for extreme pulse compression, which relies on moderately driving self-phase modulation (SPM) over an extended propagation distance. This avoids that other detrimental nonlinear mechanisms take over and deteriorate the SPM process. The long propagation is obtained by means of a hollow-core fiber (HCF), up to 6 m in length. This concept is potentially scalable to TW pulse peak powers at kW average power level. As a proof of concept, we demonstrate 33-fold pulse compression of a 1 mJ, 6 kHz, 170 fs Yb laser down to 5.1 fs (1.5 cycles at 1030 nm), by employing a single HCF and subsequent chirped mirrors with an overall transmission of 70%.
I. A. Maltsev, V. M. Shabaev, R. V. Popov, Y. S. Kozhedub, G. Plunien, X. Ma, and T. Stöhlker
Electron-positron pair production in slow collisions of heavy nuclei beyond the monopole approximation
Phys. Rev. A, 98 :062709 (December 2018)
Abstract:
Electron-positron pair production in low-energy collisions of heavy nuclei is considered beyond the monopole approximation. The calculation method is based on the numerical solving of the time-dependent Dirac equation with the full two-center potential. Bound-free and free-free pair-production probabilities as well as the energy spectra of the emitted positrons are calculated for the collisions of bare uranium nuclei. The calculations are performed for collision energy near the Coulomb barrier for different values of the impact parameter. The obtained results are compared with the corresponding values calculated in the monopole approximation.
K. S. Schulze
Fundamental limitations of the polarization purity of x rays
APL Phot., 3 :126106 (December 2018)
Abstract:
For a few years, x-ray polarimeters have been discussed and even used as a key method for the investigation of fundamental physical questions, from quantum electrodynamics to solid state physics. However, the sensitivity of optical instruments is limited. In the case of x-ray polarimeters, this limitation is connected with the polarization purity. This article quantifies two fundamental effects which lead to a limited polarization purity and, thus, to a limited sensitivity: the divergence of the source and multiple-wave diffraction inside the polarizer crystals. A comparison shows that the current best polarization purities realized in the x-ray range are limited by these effects. The quantitative knowledge of their influence, however, can improve the purity by two orders of magnitude in future polarimetric experiments.
A. H. Woldegeorgis, B. Beleites, F. Ronneberger, R. Grosse, and A. Gopal
Investigating the influence of incident laser wavelength and polarization on particle acceleration and terahertz generation
Phys. Rev. E, 98 :061201 (December 2018)
Abstract:
The interaction of a high-power laser pulse with a thin foil can generate energetic, broadband terahertz radiation. Here, we report an experimental investigation on the influence of incident laser polarization and wavelength on the terahertz emission and maximum proton energy from the target rear surface. For similar incident laser intensities, the characteristics of the particle beams and the terahertz radiation show a wavelength dependence. The results fit well with the established scaling laws for the terahertz yield and the maximum proton energy as a function of the incident laser irradiance.
C. Gaida, M. Gebhardt, T. Heuermann, F. Stutzki, C. Jauregui, and J. Limpert
Ultrafast thulium fiber laser system emitting more than 1  kW of average power
Opt. Lett., 43 :5853 (December 2018)
Abstract:
In this Letter, we report on the generation of 1060 W average power from an ultrafast thulium-doped fiber chirped pulse amplification system. After compression, the pulse energy of 13.2 μJ with a pulse duration of 265 fs at an 80 MHz pulse repetition rate results in a peak power of 50 MW spectrally centered at 1960 nm. Even though the average heat-load in the fiber core is as high as 98 W/m, we confirm the diffraction-limited beam quality of the compressed output. Furthermore, the evolution of the relative intensity noise with increasing average output power has been measured to verify the absence of transversal mode instabilities. This system represents a new average power record for thulium-doped fiber lasers (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality, in general, even considering single-channel ytterbium-doped fiber amplifiers.