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Publikationen von
Dr. Bernhard Zielbauer

Alle Publikationen des HI Jena


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.


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.


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.


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.

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.


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.


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.


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.


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.

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.


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.

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.

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.


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.

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.


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.

J. Habib, O. Guilbaud, B. Zielbauer, D. Zimmer, M. Pittman, S. Kazamias, C. Montet, T. Kühl, and D. Ros
Low energy prepulse for 10 Hz operation of a soft-x-ray laser
Optics Express 20, 10128 (2012)

Abstract: The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.


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.

D. Ros, K. Cassou, B. Cros, S. Daboussi, J. Demailly, O. Guilbaud, S. Kazamias, J.-C. Lagron, G. Maynard, O. Neveu, M. Pittman, B. Zielbauer, D. Zimmer, T. Kühl, S. Lacombe, E. Porcel, M.-A. d. Penhoat, P. Zeitoun, and G. Mourou
LASERIX: An open facility for developments of EUV and soft X-ray lasers and applications—Developments of XUV sources using high power laser facilities: ILE, ELI
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 653, 76 (2011)

Abstract: LASERIX is a high-power laser facility leading to High-repetition-rate XUV laser pumped by Titanium:Sapphire laser. The aim of this laser facility is to offer Soft XRLs in the 30–7 nm range and auxiliary IR beam, which could also be used to produce synchronized XUV sources. In this contribution, the main results concerning both the development of XUV sources and their use for applications (irradiation of DNA samples) are presented, as well the present status and some perspectives for LASERIX.

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.

M. N. Quinn, X. H. Yuan, X. X. Lin, D. C. Carroll, O. Tresca, R. J. Gray, M. Coury, C. Li, Y. T. Li, C. M. Brenner, A. P. L. Robinson, D. Neely, B. Zielbauer, B. Aurand, J. Fils, T. Kühl, and P. McKenna
Refluxing of fast electrons in solid targets irradiated by intense, picosecond laser pulses
Plasma Physics and Controlled Fusion 53, 025007 (2011)

Abstract: The propagation of fast electrons produced in the interaction of relativistically intense, picosecond laser pulses with solid targets is experimentally investigated using K α emission as a diagnostic. The role of fast electron refluxing within the target, which occurs when the electrons are reflected by the sheath potentials formed at the front and rear surfaces, is elucidated. The targets consist of a Cu fluorescence layer of fixed thickness at the front surface backed with a propagation layer of CH, the thickness of which is varied to control the number of times the refluxing fast electron population transits the Cu fluorescence layer. Enhancements in the K α yield and source size are measured as the thickness of the CH layer is decreased. Comparison with analytical and numerical modelling confirms that significant refluxing occurs and highlights the importance of considering this phenomenon when deriving information on fast electron transport from laser–solid interaction experiments involving relatively thin targets.


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).

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.

D. C. Hochhaus, J. Seres, B. Aurand, B. Ecker, B. Zielbauer, D. Zimmer, C. Spielmann, and T. Kühl
Tuning the high-order harmonic lines of a Nd:Glass laser for soft X-ray laser seeding
Applied Physics B 100, 711 (2010)

Abstract: We report here more than 50% coverage of the XUV spectral range between 18 nm and 35 nm by tuning the high-order harmonics generated by a fixed frequency Nd:Glass laser system. The tuning range achieved is suitable to seed Ni-like Y, Zr and Mo soft X-ray lasers.

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.

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.