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Publikationen von
Dr. Vincent Bagnoud

Alle Publikationen des HI Jena

2022

J. B. Ohland, U. Eisenbarth, B. Zielbauer, Y. Zobus, D. Posor, J. Hornung, D. Reemts, and V. Bagnoud
Ultra-compact post-compressor on-shot wavefront measurement for beam correction at PHELIX
High Power Laser Science and Engineering 10, 18 (2022)

Abstract: In order to reach the highest intensities, modern laser systems use adaptive optics to control their beam quality. Ideally, the focal spot is optimized after the compression stage of the system in order to avoid spatio-temporal couplings. This also requires a wavefront sensor after the compressor, which should be able to measure the wavefront on-shot. At PHELIX, we have developed an ultra-compact post-compressor beam diagnostic due to strict space constraints, measuring the wavefront over the full aperture of 28 cm. This system features all-reflective imaging beam transport and a high dynamic range in order to measure the wavefront in alignment mode as well as on shot.

M. Zimmer, S. Scheuren, A. Kleinschmidt, N. Mitura, A. Tebartz, G. Schaumann, T. Abel, T. Ebert, M. Hesse, S. Zaehter, S. Vogel, O. Merle, R.-J. Ahlers, S. Pinto, M. Peschke, T. Kroell, V. Bagnoud, C. Roedel, and M. Roth
Demonstration of non-destructive and isotope-sensitive material analysis using a short-pulsed laser-driven epi-thermal neutron source
Nature Communications 13, 2051 (2022)

Abstract: High-power laser beams can be used to accelerate neutron beams. Here the authors demonstrate the application of laser-driven neutron beams to neutron resonance spectroscopy and neutron resonance imaging. Neutrons are a valuable tool for non-destructive material investigation as their interaction cross sections with matter are isotope sensitive and can be used complementary to x-rays. So far, most neutron applications have been limited to large-scale facilities such as nuclear research reactors, spallation sources, and accelerator-driven neutron sources. Here we show the design and optimization of a laser-driven neutron source in the epi-thermal and thermal energy range, which is used for non-invasive material analysis. Neutron resonance spectroscopy, neutron radiography, and neutron resonance imaging with moderated neutrons are demonstrated for investigating samples in terms of isotope composition and thickness. The experimental results encourage applications in non-destructive and isotope-sensitive material analysis and pave the way for compact laser-driven neutron sources with high application potential.

2021

J. Hornung, Y. Zobus, S. Roeder, A. Kleinschmidt, D. Bertini, M. Zepf, and V. Bagnoud
Time-resolved study of holeboring in realistic experimental conditions
Nature Communications 12, 6999 (2021)
Kein Abstract vorhandenLinkBibTeX
J. Ohland, Y. Zobus, U. Eisenbarth, B. Zielbauer, D. Reemts, and V. Bagnoud
Alignment procedure for off-axis-parabolic telescopes in the context of high-intensity laser beam transport
Optics Express 29, 34378 (2021)

Abstract: Off-axis parabolic telescopes are rarely used in high-intensity, high-energy lasers, despite their favorable properties for beam transport such as achromatism, low aberrations and the ability to handle high peak intensities. One of the major reasons for this is the alignment procedure which is commonly viewed as complicated and time consuming. In this article, we revisit off-axis parabolic telescopes in the context of beam transport in high-intensity laser systems and present a corresponding analytical model. Based on that, we propose a suitable setup that enables fast and repeatable alignment for everyday operation.

M. Zimmer, S. Scheuren, T. Ebert, G. Schaumann, B. Schmitz, J. Hornung, V. Bagnoud, C. Rödel, and M. Roth
Analysis of laser-proton acceleration experiments for development of empirical scaling laws
Physical Review E 104, 045210 (2021)
Kein Abstract vorhandenLinkBibTeX

2020

J. Hornung, Y. Zobus, P. Boller, C. Brabetz, U. Eisenbarth, T. Kühl, Zs. Major, J. Ohland, M. Zepf, B. Zielbauer, and V. Bagnoud
Enhancement of the laser-driven proton source at PHELIX
High Power Laser Science and Engineering 8, e24 (2020)

Abstract: We present a study of laser-driven ion acceleration with micrometre and sub-micrometre thick targets, which focuses on the enhancement of the maximum proton energy and the total number of accelerated particles at the PHELIX facility. Using laser pulses with a nanosecond temporal contrast of up to and an intensity of the order of, proton energies up to 93 MeV are achieved. Additionally, the conversion efficiency at incidence angle was increased when changing the laser polarization to p, enabling similar proton energies and particle numbers as in the case of normal incidence and s-polarization, but reducing the debris on the last focusing optic.

P. Boller, A. Zylstra, P. Neumayer, L. Bernstein, C. Brabetz, J. Despotopulos, J. Glorius, J. Hellmund, E. Henry, J. Hornung, J. Jeet, J. Khuyagbaatar, L. Lens, S. Roeder, Th. Stöhlker, A. Yakushev, Y. Litvinov, D. Shaughnessy, V. Bagnoud, T. Kühl, and D. Schneider
First on-line detection of radioactive fission isotopes produced by laser-accelerated protons
Scientific Reports 10, 17183 (2020)

Abstract: The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi-MeV photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around 100MeV, the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of 200J at ≈500fs duration from the PHELIX laser produced more than 10 12 protons with energies above 15MeV in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the γ -rays were registered. The identified nuclides include those that have half-lives down to 39s. These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities.

K. Schoenberg, V. Bagnoud, A. Blazevic, V. E. Fortov, D. O. Gericke, A. Golubev, D. H. H. Hoffmann, D. Kraus, I. V. Lomonosov, V. Mintsev, S. Neff, P. Neumayer, A. R. Piriz, R. Redmer, O. Rosmej, M. Roth, T. Schenkel, B. Sharkov, N. A. Tahir, D. Varentsov, and Y. Zhao
High-energy-density-science capabilities at the Facility for Antiproton and Ion Research
Physics of Plasmas 27, 043103 (2020)

Abstract: The Facility for Antiproton and Ion Research (FAIR) will employ the World's highest intensity relativistic beams of heavy nuclei to uniquely create and investigate macroscopic (millimeter-sized) quantities of highly energetic and dense states of matter. Four principal themes of research have been identified: properties of materials driven to extreme conditions of pressure and temperature, shocked matter and material equation of state, basic properties of strongly coupled plasma and warm dense matter, and nuclear photonics with a focus on the excitation of nuclear processes in plasmas, laser-driven particle acceleration, and neutron production. The research program, principally driven by an international collaboration of scientists, called the HED@FAIR collaboration, will evolve over the next decade as the FAIR project completes and experimental capabilities develop. The first programmatic research element, called “FAIR Phase 0, officially began in 2018 to test components, detectors, and experimental techniques. Phase-0 research employs the existing and enhanced infrastructure of the GSI Helmholtzzentrum für Schwerionenforschung (GSI) heavy-ion synchrotron coupled with the PHELIX high-energy, high-intensity laser. The “FAIR Day one” experimental program, presently scheduled to begin in 2025, commences the use of FAIR's heavy-ion synchrotron, coupled to new experimental and diagnostic infrastructure, to realize the envisaged high-energy-density-science research program.

M. Afshari, J. Hornung, A. Kleinschmidt, P. Neumayer, D. Bertini, and V. Bagnoud
Proton acceleration via the TNSA mechanism using a smoothed laser focus
AIP Advances 10, 035023 (2020)

Abstract: In this work, we present the results of an experiment aiming at proton acceleration using a focus with a homogeneous intensity distribution, called smoothed focus. To achieve this goal, we implemented a phase plate before the pre-amplifier of the Petawatt High-Energy Laser for Heavy Ion EXperiments laser facility. The phase plate was used for the first time at a high-power short-pulse laser. Demonstrating a low divergent ion beam was the main goal of this work. Numerical simulations using the particle-in-cell code Extendable PIC Open Collaboration estimated a 2–5 times reduction in the angular divergence of the proton beam using a phase plate due to a smoother sheath at the rear side of the target. However, the reduction in the angular divergence was not sensible according to the experimental data. A positive point is that the spectrum of protons that are generated with the smoothed beam is shifted toward lower energies, provided that the laser absorption is kept in check, compared to the Gaussian proton spectrum. Moreover, the number of protons that are generated with the smoothed beam is higher than the ones generated with the Gaussian beam.

N. A. Tahir, P. Neumayer, I. V. Lomonosov, A. Shutov, V. Bagnoud, A. R. Piriz, S. A. Piriz, and C. Deutsch
Studies of equation of state properties of high-energy-density matter generated by intense ion beams at the facility for antiprotons and ion research
Physical Review E 101, 023202 (2020)

Abstract: The work presented in this paper shows with the help of two-dimensional hydrodynamic simulations that intense heavy-ion beams are a very efficient tool to induce high energy density (HED) states in solid matter. These simulations have been carried out using a computer code BIG2 that is based on a Godunov-type numerical algorithm. This code includes ion beam energy deposition using the cold stopping model, which is a valid approximation for the temperature range accessed in these simulations. Different phases of matter achieved due to the beam heating are treated using a semiempirical equation-of-state (EOS) model. To take care of the solid material properties, the Prandl-Reuss model is used. The high specific power deposited by the projectile particles in the target leads to phase transitions on a timescale of the order of tens of nanosecond, which means that the sample material achieves thermodynamic equilibrium during the heating process. In these calculations we use Pb as the sample material that is irradiated by an intense uranium beam. The beam parameters including particle energy, focal spot size, bunch length, and bunch intensity are considered to be the same as the design parameters of the ion beam to be generated by the SIS100 heavy-ion synchrotron at the Facility for Antiprotons and Ion Research (FAIR), at Darmstadt. The purpose of this work is to propose experiments to measure the EOS properties of HED matter including studies of the processes of phase transitions at the FAIR facility. Our simulations have shown that depending on the specific energy deposition, solid lead will undergo phase transitions leading to an expanded hot liquid state, two-phase liquid-gas state, or the critical parameter regime. In a similar manner, other materials can be studied in such experiments, which will be a very useful addition to the knowledge in this important field of research.

2019

V. Bagnoud, J. Hornung, M. Afshari, U. Eisenbarth, C. Brabetz, Z. Major, and B. Zielbauer
Implementation of a phase plate for the generation of homogeneous focal-spot intensity distributions at the high-energy short-pulse laser facility PHELIX
High Power Laser Science and Engineering 7, E62 (2019)

Abstract: We propose and demonstrate the use of random phase plates (RPPs) for high-energy sub-picosecond lasers. Contrarily to previous work related to nanosecond lasers, an RPP poses technical challenges with ultrashort-pulse lasers. Here, we implement the RPP near the beginning of the amplifier and image-relay it throughout the laser amplifier. With this, we obtain a uniform intensity distribution in the focus over an area 1600 times the diffraction limit. This method shows no significant drawbacks for the laser and it has been implemented at the PHELIX laser facility where it is now available for users.

J. B. Ohland, U. Eisenbarth, M. Roth, and V. Bagnoud
A study on the effects and visibility of low-order aberrations on laser beams with orbital angular momentum
Applied Physics B 32, 56 (2019)

Abstract: Laguerre–Gaussian-like laser beams have been proposed for driving experiments with high-intensity lasers. They carry orbital angular momentum and exhibit a ring-shaped intensity distribution in the far field which make them particularly attractive for various applications. We show experimentally and numerically that this donut-like shape is extremely sensitive to off-axis wavefront deformations. To support our claim, we generate a Laguerre–Gaussian-like laser beam and apply a selection of common low-order wavefront aberrations. We investigate the visibility of those wavefront deformations in the far field. Under use of established tolerance criteria, we determine the thresholds for the applied aberration and compare the findings with simulations for verification.

V. A. Schanz, M. Roth, and V. Bagnoud
Picosecond contrast degradation by surface imperfections in chirped-pulse-amplification stretchers
Journal of the Optical Society of America A 36, 1735 (2019)

Abstract: In this paper, we propose a study of the picosecond temporal contrast degradation of ultrashort laser pulses by surface defects in pulse stretchers. In a chirped-pulse-amplification stretcher or compressor, dust and damages on the surface of an optical element lead to a spectral amplitude modulation. Furthermore, surface figure errors of optical elements happening where the pulse is spatially dispersed yield a modulation of the spectral phase. The influence of both amplitude and phase noise effects is numerically investigated using a hybrid ray-tracing method that enables treating separately the influence of noise sources, whether noise occurs in the near field or the far field. We show that the main issue in terms of picosecond contrast degradation is a combined effect of surface pattern distortion in the far field and phase–amplitude coupling caused by spatial frequency filters. Temporal domains can be defined, where the temporal contrast is dominated by different noise effects. The algorithm used in this paper is compared to the cross-correlation trace of a pulse. The conclusions emerging from the presented analysis are universally applicable to known grating stretcher geometries.

V. A. Schanz, C. Brabetz, D. J. Posor, D. Reemts, M. Roth, and V. Bagnoud
High dynamic range, large temporal domain laser pulse measurement
Applied Physics B 125, 61 (2019)

Abstract: Temporal pulse profile characterization is necessary to ensure and quantify the quality of short pulse laser systems. Yet it remains challenging to measure the temporal behavior of a pulse in all of its comprehensiveness. In this manuscript we present results which encourage to perform more ambitious pulse characterizations with optimized scanning cross-correlators. Several temporal laser pulse profile measurements in multiple nanosecond time scale with high dynamic range are shown. The measurements were taken by our in-house third-order cross-correlator EICHEL (Schanz et al. in Opt Express 25:9252, 2017), which is able to resolve the intensity dynamics down to the level of amplified spontaneous emission. With this device we show for the first time the onset of the plateau of the amplified spontaneous emission in the laser profile and investigate the origin of several side-pulses created early in the laser system.

L. Antonelli, F. Barbato, D. Mancelli, J. Trela, G. Zeraouli, G. Boutoux, P. Neumayer, S. Atzeni, A. Schiavi, L. Volpe, V. Bagnoud, C. Brabetz, B. Zielbauer, P. Bradford, N. Woolsey, B. Borm, and D. Batani
X-ray phase-contrast imaging for laser-induced shock waves
Europhysics Letters 125, 35002 (2019)

Abstract: X-ray phase-contrast imaging (XPCI) is a versatile technique with applications in many fields, including fundamental physics, biology and medicine. Where X-ray absorption radiography requires high density ratios for effective imaging, the image contrast for XPCI is a function of the density gradient. In this letter, we apply XPCI to the study of laser-driven shock waves. Our experiment was conducted at the Petawatt High-Energy Laser for Heavy Ion EXperiments (PHELIX) at GSI. Two laser beams were used: one to launch a shock wave and the other to generate an X-ray source for phase-contrast imaging. Our results suggest that this technique is suitable for the study of warm dense matter (WDM), inertial confinement fusion (ICF) and laboratory astrophysics.

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
Contributions to Plasma Physics 59, e2018001 (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.

2018

J. Y. Mao, O. Rosmej, Y. Ma, M. H. Li, B. Aurand, F. Gaertner, W. M. Wang, J. Urbancic, A. Schoenlein, B. Zielbauer, U. Eisenbarth, V. Bagnoud, F. Wagner, F. Horst, M. Syha, S. Mathias, Y. T. Li, M. Aeschlimann, L. M. Chen, and T. Kuehl
Energy enhancement of the target surface electron by using a 200 TW sub-picosecond laser
Optics Letters 43, 3909 (2018)

Abstract: One order of magnitude energy enhancement of the target surface electron beams with central energy at 11.5 MeV is achieved by using a 200 TW, 500 fs laser at an incident angle of 72° with a prepulse intensity ratio of 5×10−6. The experimental results demonstrate the scalability of the acceleration process to high electron energy with a longer (sub-picosecond) laser pulse duration and a higher laser energy (120 J). The total charge of the beam is 400±20  pC(E>2.7  MeV). Such a high orientation and mono-energetic electron jet would be a good method to solve the problem of the large beam divergence in fast ignition schemes and to increase the laser energy deposition on the target core.

A. Kleinschmidt, V. Bagnoud, O. Deppert, A. Favalli, S. Frydrych, J. Hornung, D. Jahn, G. Schaumann, A. Tebartz, F. Wagner, G. Wurden, B. Zielbauer, and M. Roth
Intense, directed neutron beams from a laser-driven neutron source at PHELIX
Physics of Plasmas 25, 053101 (2018)

Abstract: Laser-driven neutrons are generated by the conversion of laser-accelerated ions via nuclear reactions inside a converter material. We present results from an experimental campaign at the PHELIX laser at GSI in Darmstadt where protons and deuterons were accelerated from thin deuterated plastic foils with thicknesses in the μm and sub-μm range. The neutrons were generated inside a sandwich-type beryllium converter, leading to reproducible neutron numbers around 10^11 neutrons per shot. The angular distribution was measured with a high level of detail using up to 30 bubble detectors simultaneously. It shows a laser forward directed component of up to 1.42 × 10^10 neutrons per steradian, corresponding to a dose of 43 mrem scaled to a distance of 1 m from the converter.

P. Hilz, T. M. Ostermayr, A. Huebl, V. Bagnoud, B. Borm, M. Bussmann, M. Gallei, J. Gebhard, D. Haffa, J. Hartmann, T. Kluge, F. H. Lindner, P. Neumayr, C. G. Schaefer, U. Schramm, P. G. Thirolf, T. .F. Rösch, F. Wagner, B. Zielbauer, and J. Schreiber
Isolated proton bunch acceleration by a petawatt laser pulse
Nature Communications 9, 423 (2018)

Abstract: Often, the interpretation of experiments concerning the manipulation of the energy distribution of laser-accelerated ion bunches is complicated by the multitude of competing dynamic processes simultaneously contributing to recorded ion signals. Here we demonstrate experimentally the acceleration of a clean proton bunch. This was achieved with a microscopic and three-dimensionally confined near critical density plasma, which evolves from a 1 µm diameter plastic sphere, which is levitated and positioned with micrometer precision in the focus of a Petawatt laser pulse. The emitted proton bunch is reproducibly observed with central energies between 20 and 40 MeV and narrow energy spread (down to 25%) showing almost no low-energetic background. Together with three-dimensional particle-in-cell simulations we track the complete acceleration process, evidencing the transition from organized acceleration to Coulomb repulsion. This reveals limitations of current high power lasers and viable paths to optimize laser-driven ion sources.

2017

W. Cayzac, A. Frank, A. Ortner, V. Bagnoud, M. M. Basko, S. Bedacht, C. Bläser, A. Blažević, S. Busold, O. Deppert, J. Ding, M. Ehret, P. Fiala, S. Frydrych, D. O. Gericke, L. Hallo, J. Helfrich, D. Jahn, E. Kjartansson, A. Knetsch, D. Kraus, G. Malka, N. W. Neumann, K. Pépitone, D. Pepler, S. Sander, G. Schaumann, T. Schlegel, N. Schroeter, D. Schumacher, and M. Seibert
Experimental discrimination of ion stopping models near the Bragg peak in highly ionized matter
Nature Communications 8, 15693 (2017)

Abstract: The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the α-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where theory agrees with the data. Here, we report experimental data at low projectile velocities near the Bragg peak, where the stopping force reaches its maximum. This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to disprove several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions.

V. Bagnoud, J. Hornung, T. Schlegel, B. Zielbauer, C. Brabetz, M. Roth, P. Hilz, M. Haug, J. Schreiber, and F. Wagner
Studying the Dynamics of Relativistic Laser-Plasma Interaction on Thin Foils by Means of Fourier-Transform Spectral Interferometry
Physical Review Letters 118, 255003 (2017)

Abstract: We apply Fourier-transform spectral interferometry (FTSI) to study the interaction of intense laser pulses with ultrathin targets. Ultrathin submicrometer-thick solid CH targets were shot at the PHELIX laser facility with an intensity in the mid to upper 10^19  W/cm2 range using an innovative double-pulse structure. The transmitted pulse structure was analyzed by FTSI and shows a transition from a relativistic transparency-dominated regime for targets thinner than 500 nm to a hole-boring-dominated laser-plasma interaction for thicker targets. The results also confirm that the inevitable preplasma expansion happening during the rising slope of the pulse, a few picoseconds before the maximum of the pulse is reached, cannot be neglected and plays a dominant role in laser-plasma interaction with ultrathin solid targets.

V. A. Schanz, F. Wagner, M. Roth, and V. Bagnoud
Noise reduction in third order cross-correlation by angle optimization of the interacting beams
Optics Express 25, 9252 (2017)

Abstract: We report on a novel technique to reduce the noise level in scanning third order cross-correlation. Large angles between the interacting beams combined with adapted crystal parameters lead to a significant decrease of noise photon generation while maintaining efficient generation of the third order signal. An enhanced scanning cross-correlator was developed based on the new technique proposed. In tests at the PHELIX laser facility this novel correlator performed within a dynamic range of 12.5 orders of magnitude.

F. Wagner, J. Hornung, C. Schmidt, M. Eckhardt, M. Roth, T. Stöhlker, and V. Bagnoud
Backreflection diagnostics for ultra-intense laser plasma experiments based on frequency resolved optical gating
Review of Scientific Instruments 88, 023503 (2017)

Abstract: We report on the development and implementation of a time resolved backscatter diagnostics for high power laser plasma experiments at the petawatt-class laser facility PHELIX. Pulses that are backscattered or reflected from overcritical plasmas are characterized spectrally and temporally resolved using a specially designed second harmonic generation frequency resolved optical gating system. The diagnostics meets the requirements made by typical experiments, i.e., a spectral bandwidth of more than 30nm with sub-nanometer resolution and a temporal window of 10ps with 50fs temporal resolution. The diagnostics is permanently installed at the PHELIX target area and can be used to study effects such as laser-hole boring or relativistic self-phase-modulation which are important features of laser-driven particle acceleration experiments.

2016

M. Lestinsky, V. Andrianov, B. Aurand, V. Bagnoud, D. Bernhardt, H. Beyer, S. Bishop, K. Blaum, A. Bleile, At. Borovik, F. Bosch, C. Bostock, C. Brandau, A. Bräuning-Demian, I. Bray, T. Davinson, B. Ebinger, A. Echler, P. Egelhof, A. Ehresmann, M. Engström, C. Enss, N. Ferreira, D. Fischer, A. Fleischmann, E. Förster, S. Fritzsche, R. Geithner, S. Geyer, J. Glorius, K. Göbel, O. Gorda, J. Goullon, P. Grabitz, R. Grisenti, A. Gumberidze, S. Hagmann, M. Heil, A. Heinz, F. Herfurth, R. Heß, P.-M. Hillenbrand, R. Hubele, P. Indelicato, A. Källberg, O. Kester, O. Kiselev, A. Knie, C. Kozhuharov, S. Kraft-Bermuth, T. Kühl, G. Lane, Y. Litvinov, D. Liesen, X. Ma, R. Märtin, R. Moshammer, A. Müller, S. Namba, P. Neumayer, T. Nilsson, W. Nörtershäuser, G. G. Paulus, N. Petridis, M. Reed, R. Reifarth, P. Reiß, J. Rothhardt, R. Sanchez, M. Sanjari, S. Schippers, H. Schmidt, D. Schneider, P. Scholz, R. Schuch, M. Schulz, V. Shabaev, A. Simonsson, J. Sjöholm, Ö. Skeppstedt, K. Sonnabend, U. Spillmann, K. Stiebing, M. Steck, T. Stöhlker, A. Surzhykov, S. Torilov, E. Träbert, M. Trassinelli, S. Trotsenko, X. Tu, I. Uschmann, P. Walker, G. Weber, D. Winters, P. Woods, H. Zhao, and Y. Zhang
Physics book: CRYRING@ESR
European Physical Journal Special Topics 225, 797 (2016)

Abstract: The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm and at the Test Storage Ring (TSR) at Heidelberg. For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei.

F. Wagner, O. Deppert, C. Brabetz, P. Fiala, A. Kleinschmidt, P. Poth, V. A. Schanz, A. Tebartz, B. Zielbauer, M. Roth, T. Stöhlker, and V. Bagnoud
Maximum Proton Energy above 85 MeV from the Relativistic Interaction of Laser Pulses with Micrometer Thick CH₂ Targets
Physical Review Letters 116, 205002 (2016)

Abstract: We present a study of laser-driven ion acceleration with micrometer and submicrometer thick plastic targets. Using laser pulses with high temporal contrast and an intensity of the order of 10^20  W/cm2 we observe proton beams with cutoff energies in excess of 85 MeV and particle numbers of 109 in an energy bin of 1 MeV around this maximum. We show that applying the target normal sheath acceleration mechanism with submicrometer thick targets is a very robust way to achieve such high ion energies and particle fluxes. Our results are backed with 2D particle in cell simulations furthermore predicting cutoff energies above 200 MeV for acceleration based on relativistic transparency. This predicted regime can be probed after a few technically feasible adjustments of the laser and target parameters.

W. Cayzac, A. Frank, A. Ortner, V. Bagnoud, M. Basko, S. Bedacht, A. Blažević, O. Deppert, D. Gericke, L. Hallo, A. Knetsch, D. Kraus, G. Malka, K. Pépitone, G. Schaumann, T. Schlegel, D. Schumacher, An. Tauschwitz, J. Vorberger, F. Wagner, and M. Roth
Simulations of the energy loss of ions at the stopping-power maximum in a laser-induced plasma
Journal of Physics: Conference Series 688, 012009 (2016)

Abstract: Simulations have been performed to study the energy loss of carbon ions in a hot, laser-generated plasma in the velocity region of the stopping-power maximum. In this parameter range, discrepancies of up to 30% exist between the various stopping theories and hardly any experimental data are available. The considered plasma, created by irradiating a thin carbon foil with two high-energy laser beams, is fully-ionized with a temperature of nearly 200 eV. To study the interaction at the maximum stopping power, Monte-Carlo calculations of the ion charge state in the plasma are carried out at a projectile energy of 0.5 MeV per nucleon. The predictions of various stopping-power theories are compared and experimental campaigns are planned for a first-time theory benchmarking in this low-velocity range.

2015

W. Cayzac, V. Bagnoud, M. M. Basko, A. Blazevic, A. Frank, D. O. Gericke, L. Hallo, G. Malka, A. Ortner, An. Tauschwitz, J. Vorberger, and M. Roth
Predictions for the energy loss of light ions in laser-generated plasmas at low and medium velocities
Physical Review E 92, 053109 (2015)

Abstract: The energy loss of light ions in dense plasmas is investigated with special focus on low to medium projectile energies, i.e., at velocities where the maximum of the stopping power occurs. In this region, exceptionally large theoretical uncertainties remain and no conclusive experimental data are available. We perform simulations of beam-plasma configurations well suited for an experimental test of ion energy loss in highly ionized, laser-generated carbon plasmas. The plasma parameters are extracted from two-dimensional hydrodynamic simulations, and a Monte Carlo calculation of the charge-state distribution of the projectile ion beam determines the dynamics of the ion charge state over the whole plasma profile. We show that the discrepancies in the energy loss predicted by different theoretical models are as high as 20-30%, making these theories well distinguishable in suitable experiments.

Th. Stöhlker, V. Bagnoud, K. Blaum, A. Blazevic, A. Bräuning-Demian, M. Durante, F. Herfurth, M. Lestinsky, Y. Litvinov, S. Neff, R. Pleskac, R. Schuch, S. Schippers, D. Severin, A. Tauschwitz, C. Trautmann, D. Varentsov, and E. Widmann
APPA at FAIR: From fundamental to applied research
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 365, 680 (2015)

Abstract: FAIR with its intense beams of ions and antiprotons provides outstanding and worldwide unique experimental conditions for extreme matter research in atomic and plasma physics and for application oriented research in biophysics, medical physics and materials science. The associated research programs comprise interaction of matter with highest electromagnetic fields, properties of plasmas and of solid matter under extreme pressure, density, and temperature conditions, simulation of galactic cosmic radiation, research in nanoscience and charged particle radiotherapy. A broad variety of APPA-dedicated facilities including experimental stations, storage rings, and traps, equipped with most sophisticated instrumentation will allow the APPA community to tackle new challenges. The worldwide most intense source of slow antiprotons will expand the scope of APPA related research to the exciting field of antimatter.

S. Busold, D. Schumacher, C. Brabetz, D. Jahn, F. Kroll, O. Deppert, U. Schramm, T. Cowan, A. Blazevic, V. Bagnoud, and M. Roth
Towards highest peak intensities for ultra-short MeV-range ion bunches
Scientific Reports 5, 1 (2015)

Abstract: A laser-driven, multi-MeV-range ion beamline has been installed at the GSI Helmholtz center for heavy ion research. The high-power laser PHELIX drives the very short (picosecond) ion acceleration on μm scale, with energies ranging up to 28.4 MeV for protons in a continuous spectrum. The necessary beam shaping behind the source is accomplished by applying magnetic ion lenses like solenoids and quadrupoles and a radiofrequency cavity. Based on the unique beam properties from the laser-driven source, high-current single bunches could be produced and characterized in a recent experiment: At a central energy of 7.8MeV, up to 5×10^8 protons could be re-focused in time to a FWHM bunch length of τ=(462±40) ps via phase focusing. The bunches show a moderate energy spread between 10% and 15% (ΔE/E0 at FWHM) and are available at 6m distance to the source und thus separated from the harsh laser-matter interaction environment. These successful experiments represent the basis for developing novel laser-driven ion beamlines and accessing highest peak intensities for ultra-short MeV-range ion bunches.

F. Wagner, S. Bedacht, V. Bagnoud, O. Deppert, S. Geschwind, R. Jaeger, A. Ortner, A. Tebartz, B. Zielbauer, D. H. H. Hoffmann, and M. Roth
Simultaneous observation of angularly separated laser-driven proton beams accelerated via two different mechanisms
Physics of Plasmas 22, 063110 (2015)

Abstract: We present experimental data showing an angular separation of laser accelerated proton beams. Using flat plastic targets with thicknesses ranging from 200 nm to 1200 nm, a laser intensity of 6×10²⁰ W cm⁻² incident with an angle of 10°, we observe accelerated protons in target normal direction with cutoff energies around 30 MeV independent from the target thickness. For the best match of laser and target conditions, an additional proton signature is detected along the laser axis with a maximum energy of 65 MeV. These different beams can be attributed to two acceleration mechanisms acting simultaneously, i.e., target normal sheath acceleration and acceleration based on relativistic transparency, e.g., laser breakout afterburner, respectively.

D. Kraus, J. Vorberger, J. Helfrich, D. O. Gericke, B. Bachmann, V. Bagnoud, B. Barbrel, A. Blazevic, D. C. Carroll, W. Cayzac, T. Döppner, L. B. Fletcher, A. Frank, S. Frydrych, E. J. Gamboa, M. Gauthier, S. Göde, E. Granados, G. Gregori, N. J. Hartley, B. Kettle, H. J. Lee, B. Nagler, P. Neumayer, M. M. Notley, A. Ortner, A. Otten, A. Ravasio, D. Riley, F. Roth, G. Schaumann, D. Schumacher, W. Schumaker, K. Siegenthaler, C. Spindloe, F. Wagner, K. Wünsch, S. H. Glenzer, M. Roth, and R. W. Falcone
The complex ion structure of warm dense carbon measured by spectrally resolved x-ray scattering
Physics of Plasmas 22, 056307 (2015)

Abstract: We present measurements of the complex ion structure of warm dense carbon close to the melting line at pressures around 100 GPa. High-pressure samples were created by laser-driven shock compression of graphite and probed by intense laser-generated x-ray sources with photon energies of 4.75 keV and 4.95 keV. High-efficiency crystal spectrometers allow for spectrally resolving the scattered radiation. Comparing the ratio of elastically and inelastically scattered radiation, we find evidence for a complex bonded liquid that is predicted by ab-initio quantum simulations showing the influence of chemical bonds under these conditions. Using graphite samples of different initial densities we demonstrate the capability of spectrally resolved x-ray scattering to monitor the carbon solid-liquid transition at relatively constant pressure of 150 GPa. Showing first single-pulse scattering spectra from cold graphite of unprecedented quality recorded at the Linac Coherent Light Source, we demonstrate the outstanding possibilities for future high-precision measurements at 4th Generation Light Sources.

C. João, F. Wagner, J. Körner, J. Hein, T. Gottschall, J. Limpert, and V. Bagnoud
A 10-mJ-level compact CPA system based on Yb:KGW for ultrafast optical parametric amplifier pumping
Applied Physics B 118, 401 (2015)

Abstract: A compact diode-pumped Yb:KGW regenerative amplifier producing 10 Hz, 10-mJ-level picosecond pulses at 1,040 nm is demonstrated. The system is used at the new front end of the PHELIX petawatt laser system to pump an ultrafast optical parametric amplifier for temporal contrast enhancement. Before frequency doubling, a pulse length of ∼1 ps is obtained by using a stretcher/compressor system based on a single large-aperture chirped volume Bragg grating.

C. Brabetz, S. Busold, T. Cowan, O. Deppert, D. Jahn, O. Kester, M. Roth, D. Schumacher, and V. Bagnoud
Laser-driven ion acceleration with hollow laser beams
Physics of Plasmas 22, 013105 (2015)

Abstract: The laser-driven acceleration of protons from thin foils irradiated by hollow high-intensity laser beams in the regime of target normal sheath acceleration (TNSA) is reported for the first time. The use of hollow beams aims at reducing the initial emission solid angle of the TNSA source, due to a flattening of the electron sheath at the target rear side. The experiments were conducted at the PHELIX laser facility at the GSI Helmholtzzentrum für Schwerionenforschung GmbH with laser intensities in the range from 10^18 W cm^−2 to 10^20 W cm^−2 . We observed an average reduction of the half opening angle by (3.07±0.42)° or (13.2±2.0)% when the targets have a thickness between 12 μm and 14 μm. In addition, the highest proton energies were achieved with the hollow laser beam in comparison to the typical Gaussian focal spot.

2014

F. Wagner, S. Bedacht, A. Ortner, M. Roth, A. Tauschwitz, B. Zielbauer, and V. Bagnoud
Pre-plasma formation in experiments using petawatt lasers
Optics Express 22, 29505 (2014)

Abstract: We used time-resolved shadowgraphy to characterize the pre-plasma formation in solid-target interaction experiments with micrometer-scale accuracy. We performed quantitative measurements of the plasma density for amplified spontaneous emission (ASE) levels ranging from 2 x 10^-7 to 10^-10 backed with 2-dimensional hydrodynamic simulations. We find that ASE levels above 10^-9 are able to create a significant pre-plasma plume that features a plasma canal driving a self-focusing of the laser beam. For ASE levels of 10\minus10, no ASE pre-plasma could be detected.

D. Denis-Petit, M. Comet, T. Bonnet, F. Hannachi, F. Gobet, M. Tarisien, M. Versteegen, G. Gosselin, V. Méot, P. Morel, J.-C. Pain, F. Gilleron, A. Frank, V. Bagnoud, A. Blazevic, F. Dorchies, O. Peyrusse, W. Cayzac, and M. Roth
Identification of X-ray spectra in the Na-like to O-like rubidium ions in the range of 3.8–7.3 Å
Journal of Quantitative Spectroscopy and Radiative Transfer 148, 70 (2014)

Abstract: Abstract The X-rays emitted by a rubidium plasma source created by the PHELIX laser at an intensity of about 6×1014 W/cm2 were studied. The lines have been measured using Bragg crystals in the wavelength range between 3.8 and 7.3 Å and identified by means of a numerical method developed to describe highly charged rubidium ions in LTE plasma. The experimental plasma temperature, density and charge state distributions have been estimated using non-LTE codes such as CHIVAS and AVERROES. The LTE plasma temperature and density used in the calculations are those allowing to reproduce the calculated NLTE charge state distribution. In order to optimize the use of computational resources, a criterion is established to select the configurations contributing most to the spectra among all those obtained in detailed level accounting based on the MCDF code. Seventy Rb X-rays have been identified among which forty-nine are reported for the first time. The capabilities of our method are demonstrated by the good agreement of our identifications with previously published data when available.

L. Senje, M. Yeung, B. Aurand, S. Kuschel, C. Rödel, F. Wagner, K. Li, B. Dromey, V. Bagnoud, P. Neumayer, M. Roth, C.-G. Wahlström, M. Zepf, T. Kuehl, and D. Jung
Diagnostics for studies of novel laser ion acceleration mechanisms
Review of Scientific Instruments 85, 113302 (2014)

Abstract: Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflected from and transmitted through the target and propagating in the same direction as the ion beam. Thus, the presented diagnostic constitutes a highly adaptable tool for accurately studying novel acceleration mechanisms in terms of their angular energy distribution, conversion efficiency, and plasma density evolution.

F. Wagner, C. João, J. Fils, T. Gottschall, J. Hein, J. Körner, J. Limpert, M. Roth, T. Stöhlker, and V. Bagnoud
Temporal contrast control at the PHELIX petawatt laser facility by means of tunable sub-picosecond optical parametric amplification
Applied Physics B 116, 429 (2014)

Abstract: We report on the development of a preamplifier module for temporal contrast enhancement and control at petawatt-class lasers. The module is based on an ultrafast optical parametric amplifier (uOPA), which produces temporally clean pulses at the 60 μJ level for seeding a chirped pulse amplification (CPA) system, namely the petawatt facility PHELIX. The amplifier module allows for gain reduction in the following amplifiers, resulting in an attenuation of amplified spontaneous emission (ASE) by more than 4 orders of magnitude. Since the ASE of a CPA system linearly depends on the seeding energy, we were able to demonstrate a continuous variation of the temporal contrast by tuning the gain of the uOPA.

S. Busold, A. Almomani, V. Bagnoud, W. Barth, S. Bedacht, A. Blažević, 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
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 740, 94 (2014)

Abstract: 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.

S. Busold, D. Schumacher, O. Deppert, C. Brabetz, F. Kroll, A. Blažević, V. Bagnoud, and M. Roth
Commissioning of a compact laser-based proton beam line for high intensity bunches around 10 MeV
Physical Review ST - Accelerators and Beams 17, 031302 (2014)

Abstract: We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than 10^9 particles in less than 10 ns and with tunable energy spread down to 2.7% (ΔE/E0 at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of −90  deg. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

B. Zielbauer, B. Ecker, P. Neumayer, K. Cassou, S. Daboussi, O. Guilbaud, S. Kazamias, D. Ros, T. Kuehl, U. Eisenbarth, S. Goette, D. Winters, V. Bagnoud, and Th. Stöhlker
Heavy-Ion Spectroscopy with X-Ray Lasers at GSI
X-Ray Lasers 2012 - Proceedings of the 13th International Conference on X-Ray Lasers, Springer Proceedings in Physics (2014)

Abstract: Different pumping schemes for soft X-ray lasers have been investigated at the PHELIX laser facility, including a double-target seeding approach at 18.9 nm. A technical feasibility study of using a Mo XRL beam of several μJ as an excitation source for heavy-ion spectroscopy in a storage ring has been carried out. XRL photon numbers and the beam transport under ultra-high vacuum conditions over almost 30 m are the major challenges.

2013

D. Kraus, J. Vorberger, D. O. Gericke, V. Bagnoud, A. Blazevic, W. Cayzac, A. Frank, G. Gregori, A. Ortner, A. Otten, F. Roth, G. Schaumann, D. Schumacher, K. Siegenthaler, F. Wagner, K. Wünsch, and M. Roth
Probing the Complex Ion Structure in Liquid Carbon at 100 GPa
Physical Review Letters 111, 255501 (2013)

Abstract: We present the first direct experimental test of the complex ion structure in liquid carbon at pressures around 100 GPa, using spectrally resolved x-ray scattering from shock-compressed graphite samples. Our results confirm the structure predicted by ab initio quantum simulations and demonstrate the importance of chemical bonds at extreme conditions similar to those found in the interiors of giant planets. The evidence presented here thus provides a firmer ground for modeling the evolution and current structure of carbon-bearing icy giants like Neptune, Uranus, and a number of extrasolar planets.

S. Busold, D. Schumacher, O. Deppert, C. Brabetz, S. Frydrych, F. Kroll, M. Joost, H. Al-Omari, A. Blazevic, B. Zielbauer, I. Hofmann, V. Bagnoud, T. E. Cowan, and M. Roth
Focusing and transport of high-intensity multi-MeV proton bunches from a compact laser-driven source
Physical Review ST - Accelerators and Beams 16, 101302 (2013)

Abstract: Laser ion acceleration provides for compact, high-intensity ion sources in the multi-MeV range. Using a pulsed high-field solenoid, for the first time high-intensity laser-accelerated proton bunches could be selected from the continuous exponential spectrum and delivered to large distances, containing more than 109 particles in a narrow energy interval around a central energy of 9.4 MeV and showing ≤ 30  mrad envelope divergence. The bunches of only a few nanoseconds bunch duration were characterized 2.2 m behind the laser-plasma source with respect to arrival time, energy width, and intensity as well as spatial and temporal bunch profile.

D. F. A. Winters, V. Bagnoud, B. Ecker, U. Eisenbarth, S. Götte, T. Kühl, P. Neumayer, C. Spielmann, Th. Stöhlker, and B. Zielbauer
A beamline for x-ray laser spectroscopy at the experimental storage ring at GSI
Physica Scripta 2013, 014089 (2013)

Abstract: By combining an x-ray laser (XRL) with a heavy-ion storage ring, precision laser spectroscopy of the fine-structure splitting in heavy Li-like ions will be possible. An initial study has been performed to determine the feasibility of a first experiment at the experimental storage ring at GSI in Darmstadt, which also has great potential for the experiments planned for FAIR. We plan to perform a unique, direct and precise measurement of a fine-structure transition in a heavy Li-like ion. Such a measurement will test state-of-the-art atomic structure calculations in strong fields. This endeavour will require that the existing infrastructure is complemented by a dedicated beamline for the XRL. In this paper, we will discuss the details of this project and outline a proof-of-principle experiment.

Th. Stöhlker, Y. A. Litvinov, V. Bagnoud, U. Bechstedt, C. Dimopoulou, A. Dolinskii, C. Geppert, S. Hagmann, T. Katayama, T. Kühl, R. Maier, W. Nörtershäuser, D. Prasuhn, R. Schuch, M. Steck, and H. Stockhorst
SPARC experiments at the high-energy storage ring
Physica Scripta 2013, 014085 (2013)

Abstract: The physics program of the SPARC collaboration at the Facility for Antiproton and Ion Research (FAIR) focuses on the study of collision phenomena in strong and even extreme electromagnetic fields and on the fundamental interactions between electrons and heavy nuclei up to bare uranium. Here we give a short overview on the challenging physics opportunities of the high-energy storage ring at FAIR for future experiments with heavy-ion beams at relativistic energies with particular emphasis on the basic beam properties to be expected.

2011

R. J. Gray, X. H. Yuan, D. C. Carroll, C. M. Brenner, M. Coury, M. N. Quinn, O. Tresca, B. Zielbauer, B. Aurand, V. Bagnoud, J. Fils, T. Kühl, X. X. Lin, C. Li, Y. T. Li, M. Roth, D. Neely, and P. McKenna
Surface transport of energetic electrons in intense picosecond laser-foil interactions
Applied Physics Letters 99, 171502 (2011)

Abstract: The angular distribution of energetic electrons emitted from thin foil targets irradiated by intense, picosecond laser pulses is measured as a function of laser incidence angle, intensity, and polarization. Although the escaping fast electron population is found to be predominantly transported along the target surface for incidence angles ≥ 65°, in agreement with earlier work at lower intensities, rear-surface proton acceleration measurements reveal that a significant electron current is also transported longitudinally within the target, irrespective of incident angle. These findings are of interest to many applications of laser-solid interactions, including advanced schemes for inertial fusion energy.

B. Aurand, J. Seres, V. Bagnoud, B. Ecker, D. C. Hochhaus, P. Neumayer, E. Seres, C. Spielmann, B. Zielbauer, D. Zimmer, and T. Kühl
Laser driven X-ray parametric amplification in neutral gases-a new brilliant light source in the XUV
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 653, 130 (2011)

Abstract: In this paper we present the experimental setup and results showing a new type of strong-field parametric amplification of high-order harmonic radiation. With a simple semi-classical model, we can identify the most important experimental parameters, the spectral range and the small signal gain in gases. Using a single stage amplifier, a small signal gain of 8000 has been obtained in argon for the spectral range of 40 - 50 eV, using 350 fs, 7 mJ pulses at 1.05 μm. An outlook for an experiment employing a double stage gas system will be given.

O. Tresca, D. C. Carroll, X. H. Yuan, B. Aurand, V. Bagnoud, C. M. Brenner, M. Coury, J. Fils, R. J. Gray, T. Kühl, C. Li, Y. T. Li, X. X. Lin, M. N. Quinn, R. G. Evans, B. Zielbauer, M. Roth, D. Neely, and P. McKenna
Controlling the properties of ultraintense laser–proton sources using transverse refluxing of hot electrons in shaped mass-limited targets
Plasma Physics and Controlled Fusion 53, 105008 (2011)

Abstract: We report on the transverse refluxing of energetic electrons in mass-limited foil targets irradiated with high intensity (1 × 10^{19}  W cm^{−2}), picosecond laser pulses. It is shown experimentally that the maximum energies of protons accelerated by sheath fields formed at the rear and at the edges of the target increase with decreasing target size. This is due to the modification of the sheath field by the energetic electrons which spread laterally along the target surface and reflect from the edges. In addition, it is shown that this transverse refluxing of energetic electrons can be used to tailor the spatial-intensity distribution of the proton beam by engineering the shape and size of the target.

2010

J. Seres, E. Seres, B. Ecker, D. Hochhaus, D. Zimmer, V. Bagnoud, B. Aurand, B. Zielbauer, C. Spielmann, and T. Kühl
Reply to 'The super-quadratic growth of high-harmonic signal as a function of pressure'
Nature Physics 6, 928 (2010)

Abstract: The high-harmonic generation (HHG) yield depends on several important experimental parameters and can be described with models including single atom response and propagation effects. In our recent paper we extended this description by adding a stimulated emission process and named it self-seeded X-ray parametric amplification (XPA).

V. Bagnoud, B. Aurand, A. Blazevic, S. Borneis, C. Bruske, B. Ecker, U. Eisenbarth, J. Fils, A. Frank, E. Gaul, S. Götte, C. Häfner, T. Hahn, K. Harres, H.-M. Heuck, D. Hochhaus, D. H. H. Hoffmann, D. Javorkova, H.-J. Kluge, T. Kühl, S. Kunzer, M. Kreutz, T. Merz-Mantwill, P. Neumayer, E. Onkels, D. Reemts, O. Rosmej, M. Roth, Th. Stöhlker, A. Tauschwitz, B. Zielbauer, D. Zimmer, and K. Witte
Commissioning and early experiments of the PHELIX facility
Applied Physics B 100, 137 (2010)

Abstract: At the Helmholtz center GSI, PHELIX (Petawatt High Energy Laser for heavy Ion eXperiments) has been commissioned for operation in stand-alone mode and, in combination with ions accelerated up to an energy of 13 MeV/u by the heavy ion accelerator UNILAC. The combination of PHELIX with the heavy-ion beams available at GSI enables a large variety of unique experiments. Novel research opportunities are spanning from the study of ion-matter interaction, through challenging new experiments in atomic physics, nuclear physics, and astrophysics, into the field of relativistic plasma physics.

D. Zimmer, D. Ros, O. Guilbaud, J. Habib, S. Kazamias, B. Zielbauer, V. Bagnoud, B. Ecker, D. C. Hochhaus, B. Aurand, P. Neumayer, and T. Kühl
Short-wavelength soft-x-ray laser pumped in double-pulse single-beam non-normal incidence
Physical Review A 82, 013803 (2010)

Abstract: We demonstrated a 7.36 nm Ni-like samarium soft-x-ray laser, pumped by 36 J of a neodymium:glass chirped-pulse amplification laser. Double-pulse single-beam non-normal-incidence pumping was applied for efficient soft-x-ray laser generation. In this case, the applied technique included a single-optic focusing geometry for large beam diameters, a single-pass grating compressor, traveling-wave tuning capability, and an optimized high-energy laser double pulse. This scheme has the potential for even shorter-wavelength soft-x-ray laser pumping.

V. Bagnoud, J. Fils, J. Hein, M. C. Kaluza, G. G. Paulus, Th. Stöhlker, and M. Wolf
High‐Contrast Ultrafast OPA Module For The PHELIX Facility
AIP Conference Proceedings 1228, 217 (2010)

Abstract: In this paper, a new system for improvement of the pulse contrast in CPA laser systems by use of an ultrafast OPA is reviewed together with a scheme to create sub‐picosecond synchronized OPA pump pulses. The scheme is being implemented at the PHELIX facility at GSI‐Darmstadt, Germany.

J. Seres, E. Seres, D. Hochhaus, B. Ecker, D. Zimmer, V. Bagnoud, T. Kühl, and C. Spielmann
Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases
Nature Physics 6, 455–461 (2010)

Abstract: We present a new method for parametric amplification of soft-X-ray radiation. The laser-driven amplifier is based on parametric stimulated emission and is seeded with high-order-harmonic radiation generated in the same medium. The exponential increase of the soft-X-ray yield with increasing atomic density is experimentally demonstrated for two different sets of laser parameters. A small-signal gain up to 8 × 10^{3} is obtained in both experiments at about 40 eV in argon using 350-fs-long laser pulses and with 6-fs-long ones at about 260 eV in helium, respectively. This new scheme reduces the pumping threshold for lasing with a comparable conversion efficiency into the millijoule level, which is about two orders of magnitude smaller compared with the conventional plasma X-ray lasers. With a simple model, we can estimate the necessary experimental conditions for identifying the spectral range and the magnitude of the maximum gain, which are in reasonable agreement with our measurements.

T. Kühl, B. Aurand, V. Bagnoud, B. Ecker, U. Eisenbarth, O. Guilbaud, J. Fils, S. Goette, J. Habib, D. Hochhaus, D. Javorkova, P. Neumayer, S. Kazamias, M. Pittman, D. Ros, J. Seres, C. Spielmann, B. Zielbauer, and D. Zimmer
Progress in the applicability of plasma X-ray lasers
Hyperfine Interactions 196, 233 (2010)

Abstract: Proposed as satellite-based weapons during the 1980s, X-ray lasing was for a long time only achieved with enormous amounts of pump energy in either nuclear explosions or at kilojoule-class laser installations. During the last few years a tremendous development was achieved, most visible in the realisation of the FEL lasers at DESY and SLAC. As important for a wider applicability is the enormous reduction in pump energy for laser pumped plasma X-ray lasers, which now brings such devices into the range of applications for diagnostics and spectroscopy even in smaller laboratories. Main developments were the transient excitation scheme and the optimized pumping concepts. This paper concentrates on developments at the GSI Helmholtzcenter at Darmstadt aiming towards reliable X-ray laser sources in the range from 50 to several 100 eV. The main driving forces for the laser development at GSI are the possible application for the spectroscopy of Li-like ions in the storage ring ESR and the future storage ring NESR at FAIR, and the interest in novel plasma diagnostics.

D. Zimmer, B. Zielbauer, M. Pittman, O. Guilbaud, J. Habib, S. Kazamias, D. Ros, V. Bagnoud, and T. Kühl
Optimization of a tabletop high-repetition-rate soft x-ray laser pumped in double-pulse single-beam grazing incidence
Optics Letters 35, 450 (2010)

Abstract: This Letter reports on the optimization of a tabletop nickel-like molybdenum transient collisionally excited soft x-ray laser (SXRL) at 18.9 nm performed by a double-pulse single-beam grazing incidence pumping (DGRIP). This scheme allows for the first time, to our knowledge, the full control of the pump laser parameters including the pre-pulse duration optimally generating the SXRL amplifier under a grazing incidence. The single-beam geometry of the collinear double-pulse propagation guarantees the ideal overlap of the pre-pulse and main pulse from shot to shot resulting in a more efficient and highly stable SXRL output. SXRL energies up to 2.2 µJ are obtained with a total pump energy less than 1 J for several hours at a 10 Hz repetition rate without realignment under once optimized double pumping pulse parameters including energy ratio, time delay, pre-pulse and main pulse durations, and line focus width.