Peer-Review Publications


J. Hein, M. Hornung, R. Bödefeld, S. Podleska, A. Sävert, R. Wachs, A. Kessler, S. Keppler, M. Wolf, J. Polz, O. Jäckel, M. Nicolai, M. Schnepp, J. Körner, M.C. Kaluza, and G.G. Paulus
Multiterawatt peak power generated by the all diode pumped laser—POLARIS
AIP Conf. Proc., 1228 :159 (April 2010)
At the Institute of Optics and Quantum Electronics, University of Jena, a fully diode pumped ultrahigh peak power laser system—POLARIS—has been realized. Presently, this laser system reaches a peak power of some ten terawatt. The last amplifier, which will boost the output energy to the 100 J level, is nearly completed and will be soon commissioned. The applied technologies and the basic design are reviewed here.
F. Tavella, A. Willner, J. Rothhardt, S. Hädrich, E. Seise, S. Duesterer, T. Tschentscher, H. Schlarb, J. Feldhaus, J. Limpert, A. Tünnermann, and J. Rossbach
Fiber-amplifier pumped high average power few-cycle pulse non-collinear OPCPA
Opt. Express, 18 :4689 (March 2010)
We report on the performance of a 60 kHz repetition rate sub-10 fs, optical parametric chirped pulse amplifier system with 2 W average power and 3 GW peak power. This is to our knowledge the highest average power sub-10 fs kHz-amplifier system reported to date. The amplifier is conceived for applications at free electron laser facilities and is designed such to be scalable in energy and repetition rate.
Q. Zhong, T. Aumann, S. Bishop, K. Blaum, K. Boretzky, F. Bosch, H. Bräuning, C. Brandau, T. Davinson, I. Dillmann, O. Ershova, H. Geissel, G. Gyürky, M. Heil, F. Käppeler, A. Kelić, C. Kozhuharov, C. Langer, T. L. Bleis, Y. A. Litvinov, G. Lotay, J. Marganiec, N. Petridis, R. Plag, U. Popp, R. Reifarth, B. Riese, C. Rigollet, C. Scheidenberger, H. Simon, T. Stöhlker, T. Szücs, G. Weber, H. Weick, D. F. A. Winters, N. Winters, and P. J. Woods
96^Ru(p,γ)97^Rh measurement at the GSI storage ring
J. Phys.: Conf. Ser., 202 :012011 (February 2010)
A pioneering experiment was recently performed at the Experimental Storage Ring (ESR) at GSI. Fully stripped ions of 96 Ru were injected into the storage ring and slowed down to a few MeV per nucleon. The 97 Rh ions from the 96 Ru(p,γ) reaction at a newly developed hydrogen jet target were detected with Double Sided Silicon Strip Detectors (DSSSD) mounted inside a pocket. The experiment and the status of the analysis at a beam energy of 11 MeV per nucleon will be presented.
S. Hädrich, T. Gottschall, J. Rothhardt, J. Limpert, and A. Tünnermann
CW seeded optical parametric amplifier providing wavelength and pulse duration tunable nearly transform limited pulses
Opt. Express, 18 :3158 (February 2010)
An optical parametric amplifier that delivers nearly transform limited pulses is presented. The center wavelength of these pulses can be tuned between 993 nm and 1070 nm and, at the same time, the pulse duration is varied between 206 fs and 650 fs. At the shortest pulse duration the pulse energy was increased up to 7.2 microJ at 50 kHz repetition rate. Variation of the wavelength is achieved by applying a tunable cw seed while the pulse duration can be varied via altering the pump pulse duration. This scheme offers superior flexibility and scaling possibilities.
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
Opt. Lett., 35 :450 (February 2010)
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.
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 Interact., 196 :233 (February 2010)
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.
S. Trotsenko, A. Kumar, A. V. Volotka, D. Banaś, H. F. Beyer, H. Bräuning, S. Fritzsche, A. Gumberidze, S. Hagmann, S. Hess, P. Jagodzinski, C. Kozhuharov, R. Reuschl, S. Salem, A. Simon, U. Spillmann, M. Trassinelli, L. C. Tribedi, G. Weber, D. Winters, and T. Stöhlker
Spectral Shape of the Two-Photon Decay of the 2 1S0 State in He-Like Tin
Phys. Rev. Lett., 104 :033001 (January 2010)
The spectral distribution of the 1s2s 1S0→1s2 1S0 two-photon decay of He-like tin was measured using a novel approach at the gas-jet target of the ESR storage ring. Relativistic collisions of Li-like projectiles with low-density gaseous matter have been exploited to selectively populate the desired 1s2s state. Compared to conventional techniques, this approach results in a substantial gain in statistical and systematic accuracy, which allowed us to achieve for the first time a sensitivity to relativistic effects on the two-photon decay spectral shape as well as to discriminate the measured spectrum for Sn from theoretical shapes for different elements along the He-isoelectronic sequence.


G. Dunne, H. Gies, and R. Schützhold
Catalysis of Schwinger vacuum pair production
Phys. Rev. D, 80 :111301 (December 2009)
We propose a new catalysis mechanism for nonperturbative vacuum electron-positron pair production, by superimposing a plane-wave x-ray probe beam with a strongly focused optical laser pulse, such as is planned at the Extreme Light Infrastructure (ELI) facility. We compute the absorption coefficient arising from vacuum polarization effects for photons below threshold in a strong electric field. This setup should facilitate the (first) observation of this nonperturbative QED effect with planned light sources such as ELI yielding an envisioned intensity of order 10^26 W/cm^2.
J. Rothhardt, S. Hädrich, T. Gottschall, T. Clausnitzer, J. Limpert, and A. Tünnermann
Compact fiber amplifier pumped OPCPA system delivering Gigawatt peak power 35 fs pulses
Opt. Express, 17 :24130 (December 2009)
We report on a compact Gigawatt peak power OPCPA system which is pumped by the second harmonic of an Yb-doped fiber amplifier and seeded by a cavity dumped Ti:Sapphire oscillator. Picosecond pump pulses for the OPCPA are generated by spectral filtering and directly amplified to 1 mJ pulse energy in several fiber amplifiers, without the need of chirped pulse amplification. Since no stretcher and compressor is required, the pump laser is very compact and easy to operate. The two stage optical parametric amplifier delivers 35 fs pulses with 53 microJ pulse energy and 1.1 GW peak power at 40 kHz repetition rate. Additionally, the scaling potential of this approach is discussed.
S. Hess, H. Bräuning, U. Spillmann, S. Geyer, S. Hagmann, C. Kozhuharov, T. Krings, A. Kumar, R. Märtin, B. E. O'Rourke, R. Reuschl, S. Trotsenko, G. Weber, D. Winters, and T. Stöhlker
Polarized tunable monoenergetic x-rays produced by radiative electron capture into the K-shell of Xe^(54+)
J. Phys.: Conf. Ser., 194 :012025 (December 2009)
Many physical processes such as bremsstrahlung, synchrotron radiaton and radiative recombination produce polarized X-rays. However, only a few facilities are able to deliver tunable monoenergetic high quality beams of almost completely polarized X-rays to the user. We used radiative electron capture (REC) into the K-shell of bare xenon to produce tunable and highly linearly polarized X-rays in a storage ring environment (Fig. 1) which we confirmed by a dedicated compton polarimeter.
D. Nodop, J. Rothhardt, S. Hädrich, J. Limpert, and A. Tünnermann
Wavelength-independent all-optical synchronization of a Q-switched 100-ps microchip laser to a femtosecond laser reference source
Appl. Phys. B, 94 :399 (December 2009)
We present a Q-switched microchip laser emitting 1064-nm pulses as short as 100 ps synchronized to a cavity dumped femtosecond laser emitting 800-nm pulses as short as 80 fs. The synchronization is achieved by presaturating the saturable absorber of the microchip laser with femtosecond pulses even though both lasers emit at widely separated wavelengths. The mean timing jitter is 40 ps and thus considerably shorter than the pulse duration of the microchip laser.
M. Trassinelli, A. Kumar, H. F. Beyer, P. Indelicato, R. Märtin, R. Reuschl, Y. S. Kozhedub, C. Brandau, H. Bräuning, S. Geyer, A. Gumberidze, S. Hess, P. Jagodzinski, C. Kozhuharov, D. Liesen, U. Spillmann, S. Trotsenko, G. Weber, D. F. A. Winters, and T. Stöhlker
Observation of the 2p_(3/2) → 2s_(1/2) intra-shell transition in He-like uranium
Europhys. Lett., 87 :63001 (September 2009)
We present the first observation of the 1s 2p^3P_2 → 1s 2s^3S_1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid-state detector. Using the 1s^(2) 2p^2P_(3/2) → 1s^(2) 2s^2S_(1/2) transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage ring, we obtained the first evaluation of the energy of an intra-shell transition for a He-like heavy ion.
G. Weber, C. Omet, R. D. DuBois, O. de Lucio, T. Stöhlker, C. Brandau, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, R. Reuschl, P. Spiller, U. Spillmann, M. Steck, M. Thomason, and S. Trotsenko
Beam lifetimes and ionization cross sections of U^(28+)
Phys. Rev. ST AB, 12 :084201 (August 2009)
Beam lifetimes of stored U^(28+) ions with energies between 10 and 180  MeV/u were measured in the heavy ion synchrotron SIS18 and in the experimental storage ring (ESR) of the GSI accelerator facility. By using the internal gas jet target of the ESR, it was possible to obtain projectile ionization cross sections for collisions with H_2 and N_2 from the lifetime data. The experimental cross sections are compared to theoretical data predicted by the n-body classical-trajectory Monte Carlo (CTMC) method of Olson et al. and to calculations of Shevelko et al. using the LOSS-R code. In addition, both theoretical approaches are probed by using the resulting cross sections as input parameters for the STRAHLSIM code, which models the beam losses and, consequently, the lifetimes in the heavy ion synchrotron SIS18. Both the cross section measurement and the SIS18 lifetime study indicate that the LOSS-R code cross sections are in better agreement with the experimental results than the n-body CTMC calculations.
J. Rothhardt, S. Hädrich, T. Gottschall, J. Limpert, A. Tünnermann, M. Rothhardt, M. Becker, S. Brückner, and H. Bartelt
Generation of flattop pump pulses for OPCPA by coherent pulse stacking with fiber Bragg gratings
Opt. Express, 17 :16332 (August 2009)
We present a simple and robust pulse shaping device based on coherent pulse stacking. The device is embedded in a polarisation maintaining step index fiber. An input pulse is sent through a fiber optical circulator. Up to four pulse replicas are reflected by fiber Bragg gratings and interfere at the output. Temperature control allows tuning of the relative pulse phases of the sub-pulses. Additionally fine tuning of the sub-pulse amplitudes is demonstrated. We experimentally generated 235 ps and 416 ps long flattop pulses with rising and falling edges shorter than 100 ps. In contrast to other pulse shaping techniques the presented setup is robust, alignment free, provides excellent beam quality and is also suitable for pulse durations up to several nanoseconds.
A. Steppke, R. Geithner, S. Hechler, R. Nawrodt, R. Neubert, W. Vodel, M. Schwickert, H. Reeg, and P. Seidel
Application of LTS-SQUIDs in Nuclear Measurement Techniques
IEEE Trans. Appl. Supercond., 19 :768 (June 2009)
Low temperature superconducting quantum interference devices (LTS SQUIDs) are used to make precision measurements of electromagnetic fields in applications ranging from biomedicine to high energy physics. We have previously described an LTS SQUID-based device for nuclear physics which employs the Cryogenic Current Comparator principle (CCC). The CCC consists of a high-performance LTS DC SQUID system, a toroidal pick-up coil, and a meander-shaped superconducting niobium shield. Theoretical investigations show that as external noise decreases, improvements in performance depend on the properties of the ferromagnetic core material embedded in the pick-up coil. Here we present the temperature- and frequency-dependence of several candidate ferromagnetic and nanocrystalline materials. We discuss these results in light of the optimization of the CCC sensor performance.
S. Hess, H. Bräuning, U. Spillmann, C. Brandau, S. Geyer, S. Hagmann, M. Hegewald, C. Kozhuharov, T. Krings, A. Kumar, R. Märtin, D. Protić, B. O'Rourke, R. Reuschl, M. Trassinelli, S. Trotsenko, G. Weber, D. F. A. Winters, and T. Stöhlker
Polarization studies of radiative electron capture into highly-charged uranium ions
J. Phys.: Conf. Ser., 163 :012072 (June 2009)
Recent advances in the development of 2D microstrip detectors open up new possibilities for hard x-ray spectroscopy, in particular for polarization studies. These detectors make ideal Compton polarimeters, which enable us to study precisely the polarization of hard x-rays. Here, we present recent results from measurements of Radiative Electron Capture into the K-shell of highly-charged uranium ions. The experiments were performed with a novel 2D Si(Li) Compton polarimeter at the Experimental Storage Ring at GSI. Stored and cooled beams of U^(91+) and U^(92+) ions, with kinetic energies of 43 MeV/u and 96 MeV/u respectively, were crossed with a hydrogen gasjet. The preliminary data analysis shows x-rays from the K-REC process, emitted perpendicularly to the ion beam, to be strongly linearly polarized.
T. Stöhlker, D. Banaś, H. Bräuning, S. Fritzsche, S. Geyer, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, A. Kumar, R. Märtin, B. E. O’Rourke, R. Reuschl, U. Spillmann, A. Surzhykov, S. Tashenov, S. Trotsenko, G. Weber, and D. F. A. Winters
Polarization and angular correlation studies of X-rays emitted in relativistic ion-atom collisions
Eur. Phys. J. ST, 169 :5 (March 2009)
Particle and photon polarization phenomena occurring in collisions of relativistic ions with matter have recently attracted particular interest. Investigations of the emitted characteristic x-ray and radiative electron capture radiation has been found to be a versatile tool for probing our present understanding of the dynamics of particles in extreme electromagnetic fields. Owing to the progress in x-ray detector technology, in addition, accurate measurements of the linear polarization for hard x-ray photons as well as the determination of the polarization plane became possible. This new diagnostic tool enables one today to derive information about the polarization of the ion beams from the photon polarization features of the radiative electron capture process.
H. Bräuning, S. Hess, S. Geyer, U. Spillmann, Ch. Kozhuharov, Th. Krings, A. Kumar, R. Märtin, D. Protić, R. Reuschl, M. Trassinelli, S. Trotsenko, G. Weber, D. Winters, and T. Stöhlker
Polarization Measurements of Radiative Electron Capture Transitions in Highly Charged Ions
AIP Conf. Proc., 1099 :117 (March 2009)
A dedicated Si(Li) Compton polarimeter combining energy and time resolution with a large detection area of 64 × 64 mm^2 and a two dimensional position resolution of 2 mm has been used for the first time to study the polarization of x‐rays emitted via radiative electron capture (REC) into the K and L‐shell of heavy highly charged ions. First data for the collision system 96.6 MeV/u U^(92+) → H_2 are presented. The angular distribution of the Compton scattered photons inside the detector indicates that both K‐ and L‐REC processes lead to the emission of strongly linearly polarized light.
A. Kumar, S. Trotsenko, A. V. Volotka, D. Banaś, H. F. Beyer, H. Bräuning, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, R. Reuschl, U. Spillmann, M. Trassinelli, G. Weber, and T. Stöhlker
Spectral shape of the 2E1 decay from 2s state in He-like tin
Eur. Phys. J. ST, 169 :19 (March 2009)
The two-photon 2E1 transition from the singlet 2s state of heliumlike tin was measured. An alternative experimental approach was adopted in the present investigation where the two-photon emission results from the decay of the 2s state by selective K-shell ionization of Li-like tin ions in relativistic collisions with a low-Z gaseous target, which allowed for a measurement of the undistorted two-photon spectral shape. The measured 2E1 energy distribution was compared with fully relativistic calculations, which predict a Z dependence of the distribution. The preliminary results indicate the best agreement with the relativistic many body calculations for tin, and thus confirm the sensitivity on Z. Detailed data analysis is still in progress.
C. Aguergaray, O. Schmidt, J. Rothhardt, D. Schimpf, D. Descamps, S. Petit, J. Limpert, and E. Cormier
Ultra-wide parametric amplification at 800 nm toward octave spanning.
Opt. Express, 17 :5153 (March 2009)
We report on a significant improvement of the total bandwidth amplified in an optical parametric process. By pumping a parametric amplifier with a broadband pump, we demonstrate amplification of a supercontinuum whose spectrum expands over nearly an octave ranging from less than 600 nm up to 1200 nm. Our amplifier stage is set to provide amplification at degeneracy in the quasi-collinear configuration with a temporally as well as angularly dispersed pump.
J. Rothhardt, S. Hädrich, J. Limpert, and A. Tünnermann
80 kHz repetition rate high power fiber amplifier flat-top pulse pumped OPCPA based on BIB₃O₆
Opt. Express, 17 :2508 (February 2009)
We present a high peak power optical parametric chirped pulse amplifier (OPCPA) seeded by a cavity dumped Ti:Sapphire oscillator. A frequency doubled high power Ytterbium-doped fiber amplifier is pumping the device. Temporal synchronization of the pump pulses is done via soliton generation in a highly nonlinear photonic crystal fiber. This soliton is fiber amplified and spectrally filtered in several fiber amplifiers. A simple birefringent pulse shaper generates a flat-top temporal pump pulse profile. Direct amplification of these pulses in large mode area fibers without using a stretcher and compressor provides significantly reduced complexity. For the first time to our knowledge broadband amplification around 800 nm central wavelength is demonstrated in BIB(3)O(6) (BIBO) crystals. The stretched Ti:Sapphire oscillator pulses are amplified up to a pulse energy of 25 microJ. Recompression with a grating compressor yields 50.7 fs pulses with 16.2 microJ pulse energy.
S. Hädrich, J. Rothhardt, T. Eidam, J. Limpert, and A. Tünnermann
High energy ultrashort pulses via hollow fiber compression of a fiber chirped pulse amplification system
Opt. Express, 17 :3913 (February 2009)
A simple, robust and compact pulse compressor for a high-repetition rate high-peak power fiber chirped pulse amplification system is presented. We use noble-gas-filled hollow fibers for spectral broadening of the optical pulses via self-phase modulation. Subsequent compression with chirped mirrors shortens the pulses by more than a factor of 10. Pulses shorter than 70 fs with pulse energies of the order of 100 µ J have been obtained resulting in a peak power up to 1GW at 30.3kHz. Additionally, nonlinear polarization rotation has been used for temporal pulse cleaning during the nonlinear compression at 30.3kHz and 100kHz, respectively.
T. Eidam, S. Hädrich, F. Röser, E. Seise, T. Gottschall, J. Rothhardt, T. Schreiber, J. Limpert, and A. Tünnermann
A 325-W-Average-Power Fiber CPA System Delivering Sub-400 fs Pulses
IEEE J. Sel. Top. Quantum Electron., 15 :187 (January 2009)
A high-average-power Yb-doped fiber chirped-pulse amplification system is presented. Compressed average power of 325 W at 40 MHz repetition rate corresponding to 8.2 muJ pulse energy is extracted. Compression in a highly efficient dielectric-grating-based compressor yields pulses as short as 375 fs, resulting in 22 MW of peak power.
J. Limpert, R. Fabian, D. Schimpf, E. Seise, T. Eidam, S. Hädrich, J. Rothhardt, C. Jauregui, and A. Tünnermann
High Repetition Rate Gigawatt Peak Power Fiber Laser Systems: Challenges, Design, and Experiment
IEEE J. Sel. Top. Quantum Electron., 15 :159 (January 2009)
We review the main challenges and give design guidelines for high-peak-power high-average-power fiber-based chirped-pulse amplification (CPA) systems. It is clearly pointed out that the lowest order fiber nonlinearity (NL), namely the self-phase modulation, limits the scalability of high-energy ultrashort pulse fiber amplifiers. Therefore, a distinguished difference arises between the consequences of accumulated nonlinear phase originating from the pulse envelope and initial weak modulations, resulting in a strong recommendation to operate an amplification system as linearly as possible in order to generate high-contrast pulses. Low-NL rare-earth-doped fibers, such as the recently available designs of photonic crystal fibers, are the key element for successful peak power scaling in fiber laser systems. In this paper, we present a detailed analysis and optimization of the extraction characteristics in connection with the accumulated nonlinear phase in such extreme fiber dimensions. Consequently, millijoule pulse energy femtosecond pulses at repetition rates in the 100 kHz range have already been demonstrated experimentally in a Yb-fiber-based CPA system that has even further scaling potential.


S. Hädrich, J. Rothhardt, F. Röser, T. Gottschall, J. Limpert, and A. Tünnermann
Degenerate optical parametric amplifier delivering sub 30 fs pulses with 2GW peak power
Opt. Express, 16 :19812 (November 2008)
Degenerated optical parametric amplification (OPA) is a well known technique to achieve broadband amplification necessary to generate ultrashort pulses. Here we present a parametric amplifier pumped by the frequency doubled output of a state-of-the-art fiber chirped pulse amplification system (FCPA) delivering mJ pulse energy at 30 kHz repetition rate and 650 fs pulse duration. The parametric amplifier and the FCPA system are both seeded by the same Yb:KGW oscillator. Additional spectral broadening of the OPA seed provides enough bandwidth for the generation of ultrashort pulses. After amplification in two 1mm BBO crystals a pulse energy of 90 microJ is yielded at 30 kHz. Subsequent compression with a sequence of chirped mirrors shortens the pulses to 29 fs while the pulse energy is as high as 81 µJ resulting in 2 GW of peak power.