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Publications by
Dr. Paul Neumayer

All publications of HI Jena


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.


F. Barbato, S. Atzeni, D. Batani, D. Bleiner, G. Boutoux, C. Brabetz, P. Bradford, D. Mancelli, P. Neumayer, A. Schiavi, J. Trela, L. Volpe, G. Zeraouli, N. Woolsey, and L. Antonelli
Quantitative phase contrast imaging of a shock-wave with a laser-plasma based X-ray source
Scientific Reports 9, 18805 (2019)

Abstract: X-ray phase contrast imaging (XPCI) is more sensitive to density variations than X-ray absorption radiography, which is a crucial advantage when imaging weakly-absorbing, low-Z materials, or steep density gradients in matter under extreme conditions. Here, we describe the application of a polychromatic X-ray laser-plasma source (duration ~0.5 ps, photon energy >1 keV) to the study of a laser-driven shock travelling in plastic material. The XPCI technique allows for a clear identification of the shock front as well as of small-scale features present during the interaction. Quantitative analysis of the compressed object is achieved using a density map reconstructed from the experimental data.

M. Schuster, V. Ludwig, B. Akstaller, M. Seifert, A. Wolf, T. Michel, P. Neumayer, S. Funk, and G. Anton
A fast alignment method for grating-based X-ray phase-contrast imaging systems
Journal of Instrumentation 14, P08003 (2019)

Abstract: The alignment of a grating-based X-ray phase-contrast interferometer is an iterative process that requires numerous steps of changing the distances and angles between the gratings. For each alignment step an image is acquired to evaluate the detected intensity signature in order to optimize the observed moire pattern. Thus, a large number of images has to be taken for the alignment procedure. This is not feasible within reasonable time at X-ray sources like X-ray backlighters where the time between two X-ray shots is on the scale of hours. Here, we report on the development of a stable and transportable setup ready-to-use for grating-based X-ray phase-contrast imaging. A comprehensive set of reference images taken at a continuous beam serves as a look-up table which enables the grating alignment within very few alignment steps. Since this method features a fast, reliable and predictable alignment, it is also beneficial for grating-based X-ray phase-contrast imaging systems at common X-ray sources.

J. Helfrich, J. Vorberger, S. Frydrych, G. Schaumann, A. Ravasio, M. Gauthier, L. Fletcher, B. Nagler, B. Barbrel, B. Bachmann, E. Gamboa, S. Göde, E. Granados, H. Lee, P. Neumayer, W. Schumaker, T. Döppner, R. Falcone, S. Glenzer, M. Roth, and D. Kraus
Investigation of the temperature in dense carbon near the solid-liquid phase transition between 100 GPa and 200 GPa with spectrally resolved X-ray scattering
High Energy Density Physics 32, 56 (2019)

Abstract: We present experiments investigating dense carbon at pressures between 100 GPa and 200 GPa and temperatures between 5,000 K and 15,000 K. High-pressure samples with different temperatures were created by laser-driven shock compression of graphite and varying the initial density from 1.53 g/cm³ to 2.21 g/cm³ and the drive laser intensity from 7.1 TW/cm² to 14.2 TW/cm². In order to deduce temperatures, spectrally resolved X-ray scattering was applied to determine ion-ion structure factors at a scattering vector of k = 4.12x10¹⁰ m⁻¹ which shows high sensitivity to temperature for the investigated sample conditions. After comparison to corresponding DFT-MD simulations, we were able to assign each structure factor a temperature. This information is indicative of the expected temperature range for the melting line of carbon at high pressures and can be compared to theoretical predictions.

B. B. L. Witte, G. Röpke, P. Neumayer, M. French, P. Sperling, V. Recoules, S. H. Glenzer, and R. Redmer
Comment on “Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime”
Physical Review E 99, 047201 (2019)

Abstract: Dharma-wardana et al. [M. W. C. Dharma-wardana et al., Phys. Rev. E 96, 053206 (2017)] recently calculated dynamic electrical conductivities for warm dense matter as well as for nonequilibrium two-temperature states termed “ultrafast matter” (UFM) [M. W. C. Dharma-wardana, Phys. Rev. E 93, 063205 (2016)]. In this Comment we present two evident reasons why these UFM calculations are neither suited to calculate dynamic conductivities nor x-ray Thomson scattering spectra in isochorically heated warm dense aluminum. First, the ion-ion structure factor, a major input into the conductivity and scattering spectra calculations, deviates strongly from that of isochorically heated aluminum. Second, the dynamic conductivity does not show a non-Drude behavior which is an essential prerequisite for a correct description of the absorption behavior in aluminum. Additionally, we clarify misinterpretations by Dharma-wardana et al. concerning the conductivity measurements of Gathers [G. R. Gathers, Int. J. Thermophys. 4, 209 (1983)].

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. J. Hartley, S. Brown, T. E. Cowan, E. Cunningham, T. Döppner, R. W. Falcone, L. B. Fletcher, S. Frydrych, E. Galtier, E. J. Gamboa, A. L. Garcia, D. O. Gericke, S. H. Glenzer, E. Granados, P. A. Heimann, H. J. Lee, M. J. MacDonald, A. J. MacKinnon, E. E. McBride, I. Nam, P. Neumayer, A. Pak, A. Pelka, I. Prencipe, A. Ravasio, M. Rödel, K. Rohatsch, A. M. Saunders, M. Schölmerich, M. Schörner, A. K. Schuster, P. Sun, T. v. Driel, J. Vorberger, and D. Kraus
Evidence for Crystalline Structure in Dynamically-Compressed Polyethylene up to 200 GPa
Scientific Reports 9, 4196 (2019)

Abstract: We investigated the high-pressure behavior of polyethylene (CH2) by probing dynamically-compressed samples with X-ray diffraction. At pressures up to 200 GPa, comparable to those present inside icy giant planets (Uranus, Neptune), shock-compressed polyethylene retains a polymer crystal structure, from which we infer the presence of significant covalent bonding. The A2/m structure which we observe has previously been seen at significantly lower pressures, and the equation of state measured agrees with our findings. This result appears to contrast with recent data from shock-compressed polystyrene (CH) at higher temperatures, which demonstrated demixing and recrystallization into a diamond lattice, implying the breaking of the original chemical bonds. As such chemical processes have significant implications for the structure and energy transfer within ice giants, our results highlight the need for a deeper understanding of the chemistry of high pressure hydrocarbons, and the importance of better constraining planetary temperature profiles.

B. Borm, D. Khaghani, and P. Neumayer
Properties of laser-driven hard x-ray sources over a wide range of laser intensities
Physics of Plasmas 26, 023109 (2019)

Abstract: We present measurements of the hard x-ray emission from targets irradiated at relativistic laser intensities, with the objective of comprehensively characterizing source properties relevant to x-ray radiography backlighting in high energy density experiments. Thin gold foil and tungsten wire targets were irradiated at peak laser intensities varying between 10¹⁸ and 10²¹ W/cm², with laser pulse energies >100 J. We have measured the absolute x-ray yield in the spectral range between 20 and 200 keV, angularly resolved over a large range of emission angles with respect to the incident laser. In addition, we have determined the x-ray source sizes for the two target types in the direction both along and across the target. The results are compared with the predictions of a simple model for the hot electron propagation, x-ray generation, collisional stopping, and expansion cooling. Based on this model, our measurements allow extraction of the laser to hot electron conversion over the wide range of intensities covered by our experiment.

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.


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.


D. Khaghani, M. Lobet, B. Borm, L. Burr, F. Gärtner, L. Gremillet, L. Movsesyan, O. Rosmej, M. Toimil-Molares, F. Wagner, and P. Neumayer
Enhancing laser-driven proton acceleration by using micro-pillar arrays at high drive energy
Scientific Reports 7, 11366 (2017)

Abstract: The interaction of micro- and nano-structured target surfaces with high-power laser pulses is being widely investigated for its unprecedented absorption efficiency. We have developed vertically aligned metallic micro-pillar arrays for laser-driven proton acceleration experiments. We demonstrate that such targets help strengthen interaction mechanisms when irradiated with high-energy-class laser pulses of intensities ~10^17–18 W/cm2. In comparison with standard planar targets, we witness strongly enhanced hot-electron production and proton acceleration both in terms of maximum energies and particle numbers. Supporting our experimental results, two-dimensional particle-in-cell simulations show an increase in laser energy conversion into hot electrons, leading to stronger acceleration fields. This opens a window of opportunity for further improvements of laser-driven ion acceleration systems.

Z. Samsonova, S. Höfer, A. Hoffmann, B. Landgraf, M. Zürch, I. Uschmann, D. Khaghani, O. Rosmej, P. Neumayer, R. Röder, L. Trefflich, C. Ronning, E. Förster, C. Spielmann, and D. Kartashov
X-ray emission generated by laser-produced plasmas from dielectric nanostructured targets
AIP Conference Proceedings 1811, 180001 (2017)

Abstract: We present an experimental study of X-ray generation from nanostructured ZnO targets. Samples of different morphology ranging from nanowires to polished surfaces are irradiated by relativistically intense femtosecond laser pulses. X-ray emission of plasma is generated by 45 fs 130 mJ laser pulses at 400 nm with picosecond temporal contrast better than 1E−9 interacting with an array of ZnO nanowires. The measured spectra indicate the existence of highly ionized states of Zn (up to He-like Zn). The obtained flux of ∼1E10 photons per laser shot at the neutral Zn Kα energies around 8.65 keV and at the Zn Heα energies around 9 keV is almost 3 times higher for nanostructured targets compared to the reference polished sample and implies 1E−4 conversion efficiency from the laser energy to the total energy of the emitted X-ray photons.


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.


U. Zastrau, P. Sperling, C. Fortmann-Grote, A. Becker, T. Bornath, R. Bredow, T. Döppner, T. Fennel, L. B. Fletcher, E. Förster, S. Göde, G. Gregori, M. Harmand, V. Hilbert, T. Laarmann, H. J. Lee, T. Ma, K. H. Meiwes-Broer, J. P. Mithen, C. D. Murphy, M. Nakatsutsumi, P. Neumayer, A. Przystawik, S. Skruszewicz, J. Tiggesbäumker, S. Toleikis, T. G. White, S. H. Glenzer, R. Redmer, and T. Tschentscher
Ultrafast electron kinetics in short pulse laser-driven dense hydrogen
Journal of Physics B: Atomic, Molecular and Optical Physics 48, 224004 (2015)

Abstract: Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of 10^15-10^16 W cm−2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40 eV for simulated delay times up to +70 fs after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30 eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.

B. Ecker, B. Aurand, D. C. Hochhaus, P. Neumayer, B. Zielbauer, E. Oliva, L. Li, T. T. T. Le, Q. Jin, H. Zhao, K. Cassou, S. Daboussi, O. Guilbaud, S. Kazamias, D. Ros, P. Zeitoun, and T. Kühl
Double-stage soft x-ray laser pumped by multiple pulses applied in grazing incidence
Journal of Physics B: Atomic, Molecular and Optical Physics 48, 144009 (2015)

Abstract: In this paper we report on results obtained with a compact double-stage molybdenum x-ray laser (XRL), operated with a total pump energy of 600 mJ. The two gain regions were pumped using the double-pulse grazing incidence pumping technique, which includes travelling wave excitation for both the seed- and the amplifier-target. In addition, the influence of an additional pre-pulse has been studied. Seeded XRL operation has been demonstrated in both schemes, resulting in XRL pulses with a divergence of 2×2 mrad. The peak brilliance of the amplified XRL of 4×10²³ photons/s/mm²/mrad² in 5×10⁻⁵ relative bandwidth was more than two orders of magnitude larger compared to the original seed pulses. The presented experimental concept provides an alternative approach to the currently more common use of high-order harmonic pulses as a seed source, well suited for applications like laser spectroscopy of highly-charged ions at a storage ring.

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.


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.

U. Zastrau, P. Sperling, A. Becker, T. Bornath, R. Bredow, T. Döppner, S. Dziarzhytski, T. Fennel, L. B. Fletcher, E. Förster, C. Fortmann, S. H. Glenzer, S. Göde, G. Gregori, M. Harmand, V. Hilbert, B. Holst, T. Laarmann, H. J. Lee, T. Ma, J. P. Mithen, R. Mitzner, C. D. 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, and R. Redmer
Equilibration dynamics and conductivity of warm dense hydrogen
Physical Review E 90, 013104 (2014)

Abstract: We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facility (FLASH) at DESY (Hamburg). Ultrafast impulsive electron heating is initiated by a ≤300-fs short x-ray burst of 92 eV photon energy. A second pulse probes the sample via x-ray scattering at jitter-free variable time delay. We show that the initial molecular structure dissociates within (0.9±0.2) ps, allowing us to infer the energy transfer rate between electrons and ions. We evaluate Saha and Thomas-Fermi ionization models in radiation hydrodynamics simulations, predicting plasma parameters that are subsequently used to calculate the static structure factor. A conductivity model for partially ionized plasma is validated by two-temperature density-functional theory coupled to molecular dynamic simulations and agrees with the experimental data. Our results provide important insights and the needed experimental data on transport properties of dense plasmas.

C. R. D. Brown, D. O. Gericke, M. Cammarata, B. I. Cho, T. Döppner, K. Engelhorn, E. Förster, C. Fortmann, D. Fritz, E. Galtier, S. H. Glenzer, M. Harmand, P. Heimann, N. L. Kugland, D. Q. Lamb, H. J. Lee, R. W. Lee, H. Lemke, M. Makita, A. Moinard, C. D. Murphy, B. Nagler, P. Neumayer, K.-U. Plagemann, R. Redmer, D. Riley, F. B. Rosmej, P. Sperling, S. Toleikis, S. M. Vinko, J. Vorberger, S. White, T. G. White, K. Wünsch, U. Zastrau, D. Zhu, T. Tschentscher, and G. Gregori
Evidence for a glassy state in strongly driven carbon
Scientific Reports 4, 5214 (2014)

Abstract: Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers. Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions. Strong Coulomb forces are predicted to induce nucleation into a crystalline ion structure within a few picoseconds. However, we observe no evidence of such phase transition after several tens of picoseconds but strong indications for an over-correlated fluid state. The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

T. G. White, N. J. Hartley, B. Borm, B. J. B. Crowley, J. W. O. Harris, D. C. Hochhaus, T. Kaempfer, K. Li, P. Neumayer, L. K. Pattison, F. Pfeifer, S. Richardson, A. P. L. Robinson, I. Uschmann, and G. Gregori
Electron-Ion Equilibration in Ultrafast Heated Graphite
Physical Review Letters 112, 145005 (2014)

Abstract: We have employed fast electrons produced by intense laser illumination to isochorically heat thermal electrons in solid density carbon to temperatures of ∼10 000  K. Using time-resolved x-ray diffraction, the temperature evolution of the lattice ions is obtained through the Debye-Waller effect, and this directly relates to the electron-ion equilibration rate. This is shown to be considerably lower than predicted from ideal plasma models. We attribute this to strong ion coupling screening the electron-ion interaction.

T. Ma, L. Fletcher, A. Pak, D. A. Chapman, R. W. Falcone, C. Fortmann, E. Galtier, D. O. Gericke, G. Gregori, J. Hastings, O. L. Landen, S. Le Pape, H. J. Lee, B. Nagler, P. Neumayer, D. Turnbull, J. Vorberger, T. G. White, K. Wünsch, U. Zastrau, S. H. Glenzer, and T. Döppner
Observations of strong ion-ion correlations in dense plasmasa)
Physics of Plasmas 21, 056302 (2014)

Abstract: Using simultaneous spectrally, angularly, and temporally resolved x-ray scattering, we measure the pronounced ion-ion correlation peak in a strongly coupled plasma. Laser-driven shock-compressed aluminum at ∼3× solid density is probed with high-energy photons at 17.9 keV created by molybdenum He-α emission in a laser-driven plasma source. The measured elastic scattering feature shows a well-pronounced correlation peak at a wave vector of k=4 Å^(−1). The magnitude of this correlation peak cannot be described by standard plasma theories employing a linear screened Coulomb potential. Advanced models, including a strong short-range repulsion due to the inner structure of the aluminum ions are however in good agreement with the scattering data. These studies have demonstrated a new highly accurate diagnostic technique to directly measure the state of compression and the ion-ion correlations. We have since applied this new method in single-shot wave-number resolved S(k) measurements to characterize the physical properties of dense plasmas.

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
Physical Review Letters 112, 105002 (2014)

Abstract: 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.

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.


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.

D. C. Hochhaus, B. Aurand, M. Basko, B. Ecker, T. Kühl, T. Ma, F. Rosmej, B. Zielbauer, and P. Neumayer
X-ray radiographic expansion measurements of isochorically heated thin wire targets
Physics of Plasmas 20, 062703 (2013)

Abstract: Solid density matter at temperatures ranging from 150 eV to < 5 eV has been created by irradiating thin wire targets with high-energy laser pulses at intensities ≈ 10^{18} W/cm^2 . Energy deposition and transport of the laser-produced fast electrons are inferred from spatially resolved Kα-spectroscopy. Time resolved x-ray radiography is employed to image the target mass density up to solid density and proves isochoric heating. The subsequent hydrodynamic evolution of the target is observed for up to 3 ns and is compared to radiation-hydrodynamic simulations. At distances of several hundred micrometers from the laser interaction region, where temperatures of 5–20 eV and small temperature gradients are found, the hydrodynamic evolution of the wire is a near axially symmetric isentropic expansion, and good agreement between simulations and radiography data confirms heating of the wire over hundreds of micrometers.


P. Neumayer, B. Aurand, R. Fraga, B. Ecker, R. E. Grisenti, A. Gumberidze, D. C. Hochhaus, A. Kalinin, M. C. Kaluza, T. Kühl, J. Polz, R. Reuschl, Th. Stöhlker, D. Winters, N. Winters, and Z. Yin
Evidence for ultra-fast heating in intense-laser irradiated reduced-mass targets
Physics of Plasmas 19, 122708 (2012)

Abstract: We report on an experiment irradiating individual argon droplets of 20 μm diameter with laser pulses of several Joule energy at intensities of 10^{19} W/cm^{2}. K-shell emission spectroscopy was employed to determine the hot electron energy fraction and the time-integrated charge-state distribution. Spectral fitting indicates that bulk temperatures up to 160 eV are reached. Modelling of the hot-electron relaxation and generation of K-shell emission with collisional hot-electron stopping only is incompatible with the experimental results, and the data suggest an additional ultra-fast (sub-ps) heating contribution. For example, including resistive heating in the modelling yields a much better agreement with the observed final bulk temperature and qualitatively reproduces the observed charge state distribution.

B. Ecker, E. Oliva, B. Aurand, D. C. Hochhaus, P. Neumayer, H. Zhao, B. Zielbauer, K. Cassou, S. Daboussi, O. Guilbaud, S. Kazamias, T. T. T. Le, D. Ros, P. Zeitoun, and T. Kühl
Gain lifetime measurement of a Ni-like Ag soft X-ray laser
Optics Express 20, 25391 (2012)

Abstract: Experimental results of a two-stage Ni-like Ag soft X-ray laser operated in a seed-amplifier configuration are presented. Both targets were pumped applying the double-pulse grazing incidence technique with intrinsic travelling wave excitation. The injection of the seed X-ray laser into the amplifier target was realized by a spherical mirror. The results show amplification of the seed X-ray laser and allow for a direct measurement of the gain lifetime. The experimental configuration is suitable for providing valuable input for computational simulations.

M. Harmand, C. D. Murphy, C. R. D. Brown, M. Cammarata, T. Döppner, S. Düsterer, D. Fritz, E. Förster, E. Galtier, J. Gaudin, S. H. Glenzer, S. Göde, G. Gregori, V. Hilbert, D. Hochhaus, T. Laarmann, H. J. Lee, H. Lemke, K. -H. Meiwes-Broer, A. Moinard, P. Neumayer, A. Przystawik, H. Redlin, M. Schulz, S. Skruszewicz, F. Tavella, T. Tschentscher, T. White, U. Zastrau, and S. Toleikis
Plasma switch as a temporal overlap tool for pump-probe experiments at FEL facilities
Journal of Instrumentation 7, P08007 (2012)

Abstract: We have developed an easy-to-use and reliable timing tool to determine the arrival time of an optical laser and a free electron laser (FEL) pulses within the jitter limitation. This timing tool can be used from XUV to X-rays and exploits high FELs intensities. It uses a shadowgraph technique where we optically (at 800 nm) image a plasma created by an intense XUV or X-ray FEL pulse on a transparent sample (glass slide) directly placed at the pump - probe sample position. It is based on the physical principle that the optical properties of the material are drastically changed when its free electron density reaches the critical density. At this point the excited glass sample becomes opaque to the optical laser pulse. The ultra-short and intense XUV or X-ray FEL pulse ensures that a critical electron density can be reached via photoionization and subsequent collisional ionization within the XUV or X-ray FEL pulse duration or even faster. This technique allows to determine the relative arrival time between the optical laser and the FEL pulses in only few single shots with an accuracy mainly limited by the optical laser pulse duration and the jitter between the FEL and the optical laser. Considering the major interest in pump-probe experiments at FEL facilities in general, such a femtosecond resolution timing tool is of utmost importance.

R. Fraga, A. Kalinin, M. Kühnel, D. C. Hochhaus, A. Schottelius, J. Polz, M. C. Kaluza, P. Neumayer, and R. E. Grisenti
Compact cryogenic source of periodic hydrogen and argon droplet beams for relativistic laser-plasma generation
Review of Scientific Instruments 83, 025102 (2012)

Abstract: We present a cryogenic source of periodic streams of micrometer-sized hydrogen and argon droplets as ideal mass-limited target systems for fundamental intense laser-driven plasma applications. The highly compact design combined with a high temporal and spatial droplet stability makes our injector ideally suited for experiments using state-of-the-art high-power lasers in which a precise synchronization between the laser pulses and the droplets is mandatory. We show this by irradiating argon droplets with multi-terawatt pulses.


U. Zastrau, V. Hilbert, C. Brown, T. Döppner, S. Dziarzhytski, E. Förster, S. H. Glenzer, S. Göde, G. Gregori, M. Harmand, D. Hochhaus, T. Laarmann, H. J. Lee, K. -H. Meiwes-Brör, P. Neumayer, A. Przystawik, P. Radcliffe, M. Schulz, S. Skruszewicz, F. Tavella, J. Tiggesbaeumker, S. Toleikis, and T. White
In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy
Journal of Instrumentation 6, P10001 (2011)

Abstract: We report on the simultaneous determination of non-linear dispersion functions and resolving power of three flat-field XUV grating spectrometers. A moderate-intense short-pulse infrared laser is focused onto technical aluminum which is commonly present as part of the experimental setup. In the XUV wavelength range of 10-19 nm, the spectrometers are calibrated using Al-Mg plasma emission lines. This cross-calibration is performed in-situ in the very same setup as the actual main experiment. The results are in excellent agreement with ray-tracing simulations. We show that our method allows for precise relative and absolute calibration of three different XUV spectrometers.

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.


P. Neumayer, B. Aurand, M. Basko, B. Ecker, P. Gibbon, D. C. Hochhaus, A. Karmakar, E. Kazakov, T. Kühl, C. Labaune, O. Rosmej, An. Tauschwitz, B. Zielbauer, and D. Zimmer
The role of hot electron refluxing in laser-generated K-alpha sources
Physics of Plasmas 17, 103103 (2010)

Abstract: A study of the contribution of refluxing electrons in the production of K-alpha radiation from high-intensity laser irradiated thin targets has been performed. Thin copper foils both freestanding, and backed by a thick substrate were irradiated with laser pulses of energies around 100 J at intensities ranging from below 10^17 to above 10^19 W/cm2. At high laser intensities we find a strong reduction in the K-alpha yield from targets backed by the substrate. The observed yield reduction is in good agreement with a simple model using hot electron spectra from particle-in-cell simulations or directly inferred from the measured bremsstrahlung emission and can therefore be interpreted as due to the suppression of hot electron refluxing. The study shows that refluxing electrons play a dominant role in high-intensity laser driven K- alpha generation and have to be taken into account in designing targets for laser driven high-flux K-alpha sources.

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.

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.