88 W 0.5 mJ femtosecond laser pulses from two coherently combined fiber amplifiers - Seise, E.; Klenke, A.; Breitkopf, S.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2011)
The generation of 0.5 mJ femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of 175 kHz producing 88 W of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach–Zehnder interferometer, which has been stabilized with a H{\"{a}nsch–Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as λ/70 rad at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.
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Coherent Control of High Harmonic Generation via Dual-Gas Multijet Arrays - Willner, A.; Tavella, F.; Yeung, M.; Dzelzainis, T.; Kamperidis, C.; Bakarezos, M.; Adams, D.; Schulz, M.; Riedel, R.; Hoffmann, M. C.; Hu, W.; Rossbach, J.; et al. (Physical Review Letters, 2011)
High harmonic generation (HHG) is a central driver of the rapidly growing field of ultrafast science. We present a novel quasiphase-matching (QPM) concept with a dual-gas multijet target leading, for the first time, to remarkable phase control between multiple HHG sources (>2) within the Rayleigh range. The alternating jet structure with driving and matching zones shows perfect coherent buildup for up to six QPM periods. Although not in the focus of the proof-of-principle studies presented here, we achieved competitive conversion efficiencies already in this early stage of development.
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Ellipticity dependence of 400 nm-driven high harmonic generation - Khan, S.; Cheng, Y.; M{\"{o}}ller, M.; Zhao, K.; Zhao, B.; Chini, M.; Paulus, G.; Chang, Z. (Applied Physics Letters, 2011)
We studied the dependence of high harmonic generation efficiency on the ellipticity of 400 nm driving laser pulses at 7.7 × 10^14 W/cm2 and compared it with the 800 nm driving laser under the same conditions. The measured decrease of high harmonic yield with the ellipticity of the 400 nm laser is ∼1.5 times slower that of the 800 nm, which agrees well with theoretical predictions based on a semi-classical model. The results indicate that it is feasible to use the generalized double optical gating with 400 nm lasers for extracting single attosecond pulses with high efficiency.
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Generation of high quality, 1.3 cycle pulses by active phase control of an octave spanning supercontinuum - Demmler, S.; Rothhardt, J.; Heidt, A. M.; Hartung, A.; Rohwer, E. G.; Bartelt, H.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2011)
Nonlinear pulse compression based on the generation of ultra-broadband supercontinuum (SC) in an all-normal dispersion photonic crystal fiber (ANDi PCF) is demonstrated. The highly coherent and smooth octave-spanning SC spectra are generated using 6 fs, 3 nJ pulses from a Ti:Sapphire oscillator for pumping a 13 mm piece of ANDi PCF. Applying active phase control has enabled the generation of 4.5 fs pulses. Additional spectral amplitude shaping has increased the bandwidth of the SC spectra further leading to nearly transform-limited pulses with a duration of 3.64 fs, which corresponds to only 1.3 optical cycles at a central wavelength of 810 nm. This is the shortest pulse duration achieved via compression of SC spectra generated in PCF to date. Due to the high stability and the smooth spectral intensity and phase distribution of the generated SC, an excellent temporal pulse quality exhibiting a pulse contrast of 14 dB with respect to the pre- and post-pulses is achieved.
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In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy - Zastrau, U.; Hilbert, V.; Brown, C.; D{\"{o}}ppner, T.; Dziarzhytski, S.; F{\"{o}}rster, E.; Glenzer, S. H.; G{\"{o}}de, S.; Gregori, G.; Harmand, M.; Hochhaus, D.; Laarmann, T.; et al. (Journal of Instrumentation, 2011)
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.
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Laser driven X-ray parametric amplification in neutral gases-a new brilliant light source in the XUV - Aurand, B.; Seres, J.; Bagnoud, V.; Ecker, B.; Hochhaus, D. C.; Neumayer, P.; Seres, E.; Spielmann, C.; Zielbauer, B.; Zimmer, D.; K{\"{u}}hl, T. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011)
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.
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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 - Ros, D.; Cassou, K.; Cros, B.; Daboussi, S.; Demailly, J.; Guilbaud, O.; Kazamias, S.; Lagron, J.-C.; Maynard, G.; Neveu, O.; Pittman, M.; Zielbauer, B.; et al. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011)
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.
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Magnetic-sublevel population and alignment for the excitation of H- and He-like uranium in relativistic collisions - Gumberidze, A.; Fritzsche, S.; Hagmann, S.; Kozhuharov, C.; Ma, X.; Steck, M.; Surzhykov, A.; Warczak, A.; St{\"{o}}hlker, T. (Physical Review A, 2011)
We have measured the alignment of the L-shell magnetic substates following the K-shell excitation of hydrogen- and helium-like uranium in relativistic collisions with a low-Z gaseous target. Within this experiment, the population distribution for the L-shell magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent deexcitation process. The results show a very distinctive behavior for the H- and He-like heavy systems. In particular, for K → L excitation of He-like uranium, a considerable alignment of the L-shell levels was observed. A comparison of our experimental findings with recent rigorous relativistic predictions provides a good qualitative and a reasonable quantitative agreement, emphasizing the importance of the magnetic-interaction and many-body effects in the strong-field domain of high-Z ions.
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Particle Self-Bunching in the Schwinger Effect in Spacetime-Dependent Electric Fields - Hebenstreit, F.; Alkofer, R.; Gies, H. (Physical Review Letters, 2011)
Nonperturbative electron-positron pair creation (the Schwinger effect) is studied based on the Dirac-Heisenberg-Wigner formalism in 1+1 dimensions. An ab initio calculation of the Schwinger effect in the presence of a simple space- and time-dependent electric field pulse is performed for the first time, allowing for the calculation of the time evolution of observable quantities such as the charge density, the particle number density or the total number of created particles. We predict a new self-bunching effect of charges in phase space due to the spatial and temporal structure of the pulse.
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Short-Time Electron Dynamics in Aluminum Excited by Femtosecond Extreme Ultraviolet Radiation - Medvedev, N.; Zastrau, U.; F{\"{o}}rster, E.; Gericke, D. O.; Rethfeld, B. (Physical Review Letters, 2011)
The femtosecond dynamics of the electrons in aluminum after an intense extreme ultraviolet pulse is investigated by Monte Carlo simulations. Transient distributions of the conduction band electrons show an almost thermalized, low-energy part and a high-energy tail. Constructing emission spectra from these data, we find excellent agreement with measurements. The radiative decay mainly reflects the colder part of the distribution, whereas the highly excited electrons dominate the bremsstrahlung spectrum. For the latter, we also find good agreement between predicted and measured energy scales.
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Surface transport of energetic electrons in intense picosecond laser-foil interactions - Gray, R. J.; Yuan, X. H.; Carroll, D. C.; Brenner, C. M.; Coury, M.; Quinn, M. N.; Tresca, O.; Zielbauer, B.; Aurand, B.; Bagnoud, V.; Fils, J.; K{\"{u}}hl, T.; et al. (Applied Physics Letters, 2011)
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.
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Controlling the properties of ultraintense laser–proton sources using transverse refluxing of hot electrons in shaped mass-limited targets - Tresca, O.; Carroll, D. C.; Yuan, X. H.; Aurand, B.; Bagnoud, V.; Brenner, C. M.; Coury, M.; Fils, J.; Gray, R. J.; K{\"{u}}hl, T.; Li, C.; Li, Y. T.; et al. (Plasma Physics and Controlled Fusion, 2011)
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.
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Fiber based polarization filter for radially and azimuthally polarized light - Jocher, C.; Jauregui, C.; Voigtl{\"{a}nder, C. and Stutzki, F. and Nolte, S. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2011)
We demonstrate a new fiber based concept to filter azimuthally or radially polarized light. This concept is based on the lifting of the modal degeneracy that takes place in high numerical aperture fibers. In such fibers, the radially and azimuthally polarized modes can be spectrally separated using a fiber Bragg grating. As a proof of principle, we filter azimuthally polarized light in a commercially available fiber in which a fiber Bragg grating has been written by a femtosecond pulsed laser.
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Generation of µW level plateau harmonics at high repetition rate - H{\"{a}drich, S. and Krebs, M. and Rothhardt, J. and Carstens, H. and Demmler, S. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2011)
The process of high harmonic generation allows for coherent transfer of infrared laser light to the extreme ultraviolet spectral range opening a variety of applications. The low conversion efficiency of this process calls for optimization or higher repetition rate intense ultrashort pulse lasers. Here we present state-of-the-art fiber laser systems for the generation of high harmonics up to 1 MHz repetition rate. We perform measurements of the average power with a calibrated spectrometer and achieved µW harmonics between 45 nm and 61 nm (H23-H17) at a repetition rate of 50 kHz. Additionally, we show the potential for few-cycle pulses at high average power and repetition rate that may enable water-window harmonics at unprecedented repetition rate.
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Improved carrier-envelope phase locking of intense few-cycle laser pulses using above-threshold ionization - Adolph, D.; Sayler, A. M.; Rathje, T.; R{\"{u}}hle, K.; Paulus, G.G. (Optics Letters, 2011)
A robust nonoptical carrier-envelope phase (CEP) locking feedback loop, which utilizes a measurement of the left–right asymmetry in the above-threshold ionization (ATI) of Xe, is implemented, resulting in a significant improvement over the standard slow-loop f-to-2f technique. This technique utilizes the floating average of a real-time, every-single-shot CEP measurement to stabilize the CEP of few-cycle laser pulses generated by a standard Ti:sapphire chirped-pulse amplified laser system using a hollow-core fiber and chirped mirror compression scheme. With this typical commercially available laser system and the stereographic ATI method, we are able to improve short-term (minutes) CEP stability after a hollow-core fiber from 450 to 290 mrad rms and long-term (hours) stability from 480 to 370 mrad rms.
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Precise, real-time, single-shot carrier-envelope phase measurement in the multi-cycle regime - M{\"{o}}ller, M.; Sayler, A. M.; Rathje, T.; Chini, M.; Chang, Z.; Paulus, G.G. (Applied Physics Letters, 2011)
Polarization gating is used to extend a real-time, single-shot, carrier-envelope phase (CEP) measurement, based on high-energy above-threshold ionization in xenon, to the multi-cycle regime. The single-shot CEP precisions achieved are better than 175 and 350 mrad for pulse durations up to 10 fs and 12.5 fs, respectively, while only 130 μJ of pulse energy are required. This opens the door to study and control of CEP-dependent phenomena in ultra-intense laser-matter interaction using optical parametric chirped pulse amplifier based tera- and petawatt class lasers.
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Single-shot velocity-map imaging of attosecond light-field control at kilohertz rate - S{\"{u}}ssmann, F.; Zherebtsov, S.; Plenge, J.; Johnson, N.; K{\"{u}}bel, M.; Sayler, A. M.; Mondes, V.; Graf, C.; R{\"{u}}hl, E.; Paulus, G.G.; Schmischke, D.; Swrschek, P.; et al. (Review of Scientific Instruments, 2011)
High-speed, single-shot velocity-map imaging (VMI) is combined with carrier-envelope phase (CEP) tagging by a single-shot stereographic above-threshold ionization (ATI) phase-meter. The experimental setup provides a versatile tool for angle-resolved studies of the attosecond control of electrons in atoms, molecules, and nanostructures. Single-shot VMI at kHz repetition rate is realized with a highly sensitive megapixel complementary metal-oxide semiconductor camera omitting the need for additional image intensifiers. The developed camera software allows for efficient background suppression and the storage of up to 10^24 events for each image in real time. The approach is demonstrated by measuring the CEP-dependence of the electron emission from ATI of Xe in strong (≈ 10^13 W/cm2) near single-cycle (4 fs) laser fields. Efficient background signal suppression with the system is illustrated for the electron emission from SiO_2 nanospheres.
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Ultrashort pulse formation and evolution in mode-locked fiber lasers - Baumgartl, M.; Ortac, B.; Schreiber, T.; Limpert, J.; T{\"{u}}nnermann, A. (Applied Physics B, 2011)
Passive mode-locking in fiber lasers is investigated by numerical and experimental means. A non-distributed scalar model solving the nonlinear Schr{\"{o}}dinger equation is implemented to study the starting behavior and intra-cavity dynamics numerically. Several operation regimes at positive net-cavity dispersion are experimentally accessed and studied in different environmentally stable, linear laser configurations. In particular, pulse formation and evolution in the chirped-pulse regime at highly positive cavity dispersion is discussed. Based on the experimental results a route to highly energetic pulse solutions is shown in numerical simulations.
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Vacuum polarization tensor in inhomogeneous magnetic fields - Gies, H.; R{\"{o}}ssler, L. (Physical Review A, 2011)
We develop worldline numerical methods, which combine string-inspired with Monte Carlo techniques, for the computation of the vacuum polarization tensor in inhomogeneous background fields for scalar QED. The algorithm satisfies the Ward identity exactly and operates on the level of renormalized quantities. We use the algorithm to study for the first time light propagation in a spatially varying magnetic field. Whereas a local derivative expansion applies to the limit of small variations compared to the Compton wavelength, the case of a strongly varying field can be approximated by a derivative expansion for the averaged field. For rapidly varying fields, the vacuum-magnetic refractive indices can exhibit a nonmonotonic dependence on the local field strength. This behavior can provide a natural limit on the self-focussing property of the quantum vacuum.
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Vortices in ultrashort laser pulses - Hansinger, P.; Dreischuh, A.; Paulus, G.G. (Applied Physics B, 2011)
The propagation of optical vortices nested in broadband femtosecond laser beams was studied both numerically and experimentally. Based on the nonlinear Schr{\"{o}}dinger equation, the dynamics of different multiple-vortex configurations with varying topological charge were modelled in self-focussing and self-defocussing Kerr media. We find a similar behavior in both cases regarding the vortex–vortex interaction. However, the collapsing background beam alters the propagation for a positive nonlinearity. Regimes of regular and possibly stable multiple filamentation were identified this way. Experiments include measurements on pairs of filaments generated in a vortex beam on an astigmatic Gaussian background with argon gas as the nonlinear medium. Spectral broadening of these filaments leads to a supercontinuum which spans from the visible range into the infrared. Recompression yields < 19 fs pulses. Further optimization may lead to much better recompression.
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Analysis and suppression of parasitic processes in noncollinear optical parametric amplifiers - Bromage, J.; Rothhardt, J.; H{\"{a}drich, S. and Dorrer, C. and Jocher, C. and Demmler, S. and Limpert, J. and T{\"{u}}nnermann, A. and Z{\"{u}}gel, J. D. (Optics Express, 2011)
The influence of parasitic processes on the performance of ultra-broadband noncollinear optical parametric amplifiers (NOPA’s) is investigated for walk-off and non-walk-off compensating configurations. Experimental results with a white-light–seeded NOPA agree well with numerical simulations. The same model shows that 10% of the output energy of an amplified signal can be transferred into a parasitic second harmonic of the signal. These findings are supported by quantitative measurements on a few-cycle NOPA, where a few percent of the signal energy is converted to its second harmonic in the walk-off compensating case. This effect is reduced by an order of magnitude in the non-walk-off compensating configuration. A detailed study of the phase-matching conditions of the most common nonlinear crystals provides guidelines for designing NOPA systems.
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Creating circularly polarized light with a phase-shifting mirror - Aurand, B.; Kuschel, S.; R{\"{o}}del, C.; Heyer, M.; Wunderlich, F.; J{\"{a}ckel, O. and Kaluza, M.C. and Paulus, G.G. and K{\"{u}}hl, T. (Optics Express, 2011)
We report on the performance of a system employing a multi-layer coated mirror creating circularly polarized light in a fully reflective setup. With one specially designed mirror we are able to create laser pulses with an ellipticity of more than ε = 98% over the entire spectral bandwidth from initially linearly polarized Titanium:Sapphire femtosecond laser pulses. We tested the homogeneity of the polarization with beam sizes of the order of approximately 10 cm. The damage threshold was determined to be nearly 400 times higher than for a transmissive quartz-wave plate which suggests applications in high intensity laser experiments. Another advantage of the reflective scheme is the absence of nonlinear effects changing the spectrum or the pulse-form and the scalability of coating fabrication to large aperture mirrors.
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High resolution 3D gas-jet characterization - Landgraf, B.; Schnell, M.; S{\"{a}vert, A. and Kaluza, M.C. and Spielmann, C. (Review of Scientific Instruments, 2011)
We present a tomographic characterization of gas jets employed for high-intensity laser-plasma interaction experiments where the shape can be non-symmetrically. With a Mach-Zehnder interferometer we measured the phase shift for different directions through the neutral density distribution of the gas jet. From the recorded interferograms it is possible to retrieve 3-dimensional neutral density distributions by tomographic reconstruction based on the filtered back projections. We report on criteria for the smallest number of recorded interferograms as well as a comparison with the widely used phase retrieval based on an Abel inversion. As an example for the performance of our approach, we present the characterization of nozzles with rectangular openings or gas jets with shock waves. With our setup we obtained a spatial resolution of less than 60 μm for an Argon density as low as 2 × 10^17 cm^−3.
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Ion Temperature and Hydrodynamic-Energy Measurements in a Z-Pinch Plasma at Stagnation - Kroupp, E.; Osin, D.; Starobinets, A.; Fisher, V.; Bernshtam, V.; Weingarten, L.; Maron, Y.; Uschmann, I.; F{\"{o}}rster, E.; Fisher, A.; Cuneo, M. E.; Deeney, C.; et al. (Physical Review Letters, 2011)
The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission.
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Momentum distributions of sequential ionization generated by an intense laser pulse - Shvetsov-Shilovski, N. I.; Sayler, A. M.; Rathje, T.; Paulus, G.G. (Physical Review A, 2011)
The relative yield and momentum distributions of all multiply charged atomic ions generated by a short (30 fs) intense (10^14 - 5 × 10^18 W/cm2) laser pulse are investigated using a Monte Carlo simulation. We predict a substantial shift in the maximum (centroid) of the ion-momentum distribution along the laser polarization as a function of the absolute phase. This effect should be experimentally detectable with currently available laser systems even for relatively long pulses, such as 25 - 30 fs. In addition to the numerical results, we present semianalytical scaling for the position of the maximum.
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Avoided crossings in photonic crystal fibers - Jansen, F.; Stutzki, F.; Jauregui, C.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2011)
The impact of avoided crossings (also known as anti-crossings) in single and double-clad large mode area Photonic Crystal Fibers (PCFs) suitable for high-power laser systems is evaluated numerically. It is pointed out that an inappropriate choice of pump core diameter, bending radius and/or index depression may lead to avoided crossings that manifest themselves in unwanted deformations of the output beam.
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Comparison of femtosecond laser-induced damage on unstructured vs. nano-structured Au-targets - Kern, C.; Z{\"{u}}rch, M.; Petschulat, J.; Pertsch, T.; Kley, B.; K{\"{a}sebier, T. and H{\"{u}}bner, U. and Spielmann, C. (Applied Physics A, 2011)
The combination of high-field physics with nano-plasmonics has proven to be feasible in producing high harmonics of intense laser radiation from noble gases, assisted by the field-enhancement effect in the proximity of metallic nano-antennas. However, the intensity region where harmonics can be generated without irreversible damage to these delicate structures is rather narrow. We explore the damage threshold of gold targets that exhibit regular structures on a nanoscopic scale, either explicitly resonant to the used laser frequency, or off-resonance. These are compared to values for bulk material in order to gain insight into the role of plasmonic resonances in the response of solid targets on intense laser radiation. We find that the presence of such a resonance lowers the threshold fluence (J/cm^2) where global structural damage sets in by about an order of magnitude. Statistical deviations either in local pulse energy of the damage inducing laser radiation or in the exact resonance behaviour of singular structures prove to be limited. These results should serve as a guideline for future experiments working near the damage threshold of more sophisticated antenna designs.
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Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers - Eidam, T.; Wirth, C.; Jauregui, C.; Stutzki, F.; Jansen, F.; Otto, H.; Schmidt, O.; Schreiber, T.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2011)
We report on the observation and experimental characterization of a threshold-like onset of mode instabilities, i.e. an apparently random relative power content change of different transverse modes, occurring in originally single-mode high-power fiber amplifiers. Although the physical origin of this effect is not yet fully understood, we discuss possible explanations. Accordingly, several solutions are proposed in this paper to raise the threshold of this effect.
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High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber - Heidt, A.; Rothhardt, J.; Hartung, A.; Bartelt, H.; Rohwer, E.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2011)
We demonstrate nonlinear pulse compression based on recently introduced highly coherent broadband supercontinuum (SC) generation in all-normal dispersion photonic crystal fiber (ANDi PCF). The special temporal properties of the octave-spanning SC spectra generated with 15 fs, 1.7 nJ pulses from a Ti:Sapphire oscillator in a 1.7 mm fiber piece allow the compression to 5.0 fs high quality pulses by linear chirp compensation with a compact chirped mirror compressor. This is the shortest pulse duration achieved to date from the external recompression of SC pulses generated in PCF. Numerical simulations in excellent agreement with the experimental results are used to discuss the scalability of the concept to the single-cycle regime employing active phase shaping. We show that previously reported limits to few-cycle pulse generation from compression of SC spectra generated in conventional PCF possessing one or more zero dispersion wavelengths do not apply for ANDi PCF.
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Precision studies of fundamental atomic structure with heaviest few-electron ions - Gumberidze, A.; St{\"{o}}hlker, T.; Bana{ś}, D.; Beyer, H. F.; Brandau, C.; Br{\"{a}uning, H. and Geyer, S. and Hagmann, S. and Hess, S. and Indelicato, P. and Jagodzinski, P. and Kozhuharov, C. and Kumar, A. and Liesen, D. and M{\"{a}rtin, R. and Reuschl, R. and Salem, S. and Simon, A. and Spillmann, U. and Trassinelli, M. and Trotsenko, S. and Weber, G. and Winters, D. F. A. (Hyperfine Interactions, 2011)
One- and few-electron ions traditionally serve as an important testing ground for fundamental atomic structure theories and for the effects of QED, relativity and electron correlation. In the domain of high nuclear charges, new opportunities open up for precise testing and consolidating of the present understanding of the atomic structure in the regime of extreme electromagnetic fields. In this review, the current progress in experimental investigations of the heaviest H- and He-like systems at GSI Darmstadt is presented together with the planned future developments.
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Prepulse suppression in a multi-10-TW diode-pumped Yb:glass laser - Keppler, S.; B{\"{o}}defeld, R.; Hornung, M.; S{\"{a}vert, A. and Hein, J. and Kaluza, M.C. (Applied Physics B, 2011)
We describe a novel method to improve the temporal intensity contrast (TIC) between the main pulse and prepulses in a high-power chirped-pulse amplification (CPA) laser system. Pre- and post-pulses originating from the limited extinction ratio of the polarization gating equipment are suppressed by carefully adjusting the round-trip times of the regenerative amplifiers (RAs) with respect to the oscillator. As a result, leaking pulses from earlier or later round-trips in the RAs are hidden below the temporal shape of the main pulse. The synchronization can easily be controlled by a contrast measurement on a picosecond time scale using a third-order cross-correlator that enables a sub-mm precise adjustment of the cavity lengths. Finally, a method based on spectral interference is introduced that can be used for a fine-adjustment of the cavity lengths for the daily operation, making this new method easy to implement into existing laser systems.
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Real-time observation of laser-driven electron acceleration - Buck, A.; Nicolai, M.; Schmid, K.; Sears, C.; S{\"{a}vert, A. and Mikhailova, J. and Krausz, F. and Kaluza, M.C. and Veisz, L. (Nature Physics, 2011)
Electron acceleration by laser-driven plasma waves is capableof producing ultra-relativistic, quasi-monoenergetic electron bunches with orders of magnitude higher accelerating gradients and much shorter electron pulses than state-of-the-art radio-frequency accelerators. Recent developments have shown peak energies reaching into the GeV range and improved stability and control over the energy spectrum and charge. Future applications, such as the development of laboratory X-ray sources with unprecedented peak brilliance or ultrafast time-resolved measurements critically rely on a temporal characterization of the acceleration process and the electron bunch. Here, we report the first real-time observation of the accelerated electron pulse and the accelerating plasma wave. Our time-resolved study allows a single-shot measurement of the (5.8_(−2.1))^(+1.9) fs electron bunch full-width at half-maximum ((2.5_(−0.9))^(+0.8) fs root mean square) as well as the plasma wave with a density-dependent period of 12–22 fs and reveals the evolution of the bunch, its position in the surrounding plasma wave and the wake dynamics. The results afford promise for brilliant, sub-{{a}}ngstr{\"{o}}m-wavelength ultrafast electron and photon sources for diffraction imaging with atomic resolution in space and time.
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Yb:YAG Innoslab amplifier: efficient high repetition rate subpicosecond pumping system for optical parametric chirped pulse amplification - Schulz, M.; Riedel, R.; Willner, A.; Mans, T.; Schnitzler, C.; Russbueldt, P.; Dolkemeyer, J.; Seise, E.; Gottschall, T.; H{\"{a}drich, S. and Duesterer, S. and Schlarb, H. and Feldhaus, J. and Limpert, J. and Faatz, B. and T{\"{u}}nnermann, A. and Rossbach, J. and Drescher, M. and Tavella, F. (Optics Letters, 2011)
We report on a Yb:YAG Innoslab laser amplifier system for generation of subpicsecond high energy pump pulses for optical parametric chirped pulse amplification (OPCPA) at high repetition rates. Pulse energies of up to 20 mJ (at 12.5 kHz) and repetition rates of up to 100 kHz were attained with pulse durations of 830 fs and average power in excess of 200 W. We further investigate the possibility to use subpicosecond pulses to derive a stable continuum in a YAG crystal for OPCPA seeding.
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A Non-Destructive Beam Monitoring System Based on an LTS-SQUID - Geithner, R.; Neubert, R.; Vodel, W.; Schwickert, M.; Reeg, H.; von Hahn, R.; Seidel, P. (IEEE Transactions on Applied Superconductivity, 2011)
Monitoring of beam currents in particle accelerators without affecting the beam guiding elements, interrupting the beam or influencing its profile is a major challenge in accelerator technology. A solution to this problem is the detection of the magnetic field generated by the moving charged particles. We present a non-destructive beam monitoring system for particle beams in accelerators based on the Cryogenic Current Comparator (CCC) principle. The CCC consists of a high-performance low-temperature DC superconducting quantum interference device (LTS DC-SQUID) system, a toroidal pick-up coil, and a meander-shaped superconducting niobium shield. This device allows the measurement of continuous as well as pulsed beam currents in the nA-range. The resolution and the frequency response of the detector strongly depend on the toroidal pick-up coil and its embedded ferromagnetic core. Investigations of both the temperature and frequency dependence of the relative permeability and the noise contribution of several nanocrystalline ferromagnetic core materials are crucial to optimize the CCC with respect to an improved signal-to-noise ratio and extended transfer bandwidth.
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Absorption of circularly polarized laser pulses in near-critical plasmas - Robinson, A. P. L.; Trines, R. M. G. M.; Polz, J.; Kaluza, M.C. (Plasma Physics and Controlled Fusion, 2011)
The absorption of an ultra-intense circularly-polarized laser pulse by a near-critical (0.1 n_c < n_e < a_0 n_c) plasma is studied. Previously two regimes of absorption have been suggested: a 'leading edge depletion' (LED) regime and a 'transverse ponderomotive acceleration' regime. Here we seek to describe these concepts more thoroughly, and determine if two distinct regimes actually exist. New analytic models to describe each regime are derived. These are compared with 1D and 2D particle-in-cell simulations, and good quantitative agreement is found, showing the existence of two separate regimes. The LED regime exhibits very efficient absorption of laser light, which is promising for applications.
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Charge-changing processes in collisions of heavy many-electron ions with neutral atoms - Shevelko, V. P.; Beigman, I. L.; Litsarev, M. S.; Tawara, H.; Tolstikhina, I. Yu.; Weber, G. (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2011)
Some features of charge-changing processes, namely, electron capture (EC) and electron loss (EL), are considered for heavy many-electron ions colliding with neutral atoms in a wide range of ion energy E = 10 keV/u – 100 GeV/u. The discussion is based on cross-section calculations performed by available computer codes, namely, CAPTURE, DEPOSIT and RICODE. The RICODE (Relativistic Ionization CODE), which provides calculation of single-electron loss cross sections in the relativistic energy regime, was recently created on the basis of the relativistic Born approximation and is described in the Appendix A. In addition, a semi-empirical formula for single-electron loss cross sections is suggested based on properties of the Born approximation and numerical calculations by the RICODE program. To cover also the low and intermediate collision energies, EL cross sections are obtained by the recently created DEPOSIT code which provides calculation of single- and multiple-electron as well as the total cross sections. Based on the results obtained by these codes, recommended capture and loss cross sections for heavy ions like xenon, uranium and lead ions colliding with neutral atoms are presented over a wide energy range.
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Differential energy measurement between He- and Li-like uranium intra-shell transitions - Trassinelli, M.; Kumar, A.; Beyer, H. F.; Indelicato, P.; M{\"{a}rtin, R. and Reuschl, R. and Kozhedub, Y. S. and Brandau, C. and Br{\"{a}uning, H. and Geyer, S. and Gumberidze, A. and Hess, S. and Jagodzinski, P. and Kozhuharov, C. and Liesen, D. and Spillmann, U. and Trotsenko, S. and Weber, G. and Winters, D. F. A. and St{\"{o}}hlker, T. (Physica Scripta, 2011)
We present the first clear identification and highly accurate measurement of the intra-shell transition 1s2p^3P_2 → 1s2s^3S_1 of He-like uranium performed via x-ray spectroscopy. The present experiment was conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany), where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the 1s2p^3P_2→1s2s^3S_1 He-like U transition energy, at 4510 eV, and the 1s^2 2p^2P_(3/2) → 1s^2 2s^2S_(1/2) Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the x-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with theory without the uncertainties arising from one-photon quantum electrodynamics predictions and nuclear size corrections.
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Laser spectroscopy of the (1s2 2s2p) 3P0–3P1 level splitting in Be-like krypton - Winters, D. F. A.; K{\"{u}}hl, T.; Schneider, D. H.; Indelicato, P.; Reuschl, R.; Schuch, R.; Lindroth, E.; St{\"{o}}hlker, T. (Physica Scripta, 2011)
Heavy few-electron ions, such as He-, Li- and Be-like ions, are ideal atomic systems to study the effects of correlation, relativity and quantum electrodynamics. Very recently, theoretical and experimental studies of these species achieved a considerable improvement in accuracy. Be-like ions are interesting because their first excited state, i.e. (1s2 2s2p)3P0, has an almost infinite lifetime (τ0) in the absence of nuclear spin (I), as it can only decay by a two-photon E1M1 transition to the (1s2 2s2)1S0 ground state. In addition, the energy difference between the 3P0 and the next higher-lying 3P1 state is expected to remain almost completely unaffected by QED effects, and should thus be dominated by the effects of correlation and relativity. Therefore, we want to determine the (1s2 2s2p) 3P0–3P1 level splitting in Be-like krypton (84Kr32+), which has I=0, by means of laser spectroscopy at the experimental storage ring at GSI. In such an experiment, the energy splitting can be obtained with very good accuracy and can be compared with recent calculations.
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Monte Carlo simulations for the characterization of position-sensitive x-ray detectors dedicated to Compton polarimetry - Weber, G.; Br{\"{a}uning, H. and M{\"{a}rtin, R. and Spillmann, U. and St{\"{o}}hlker, T. (Physica Scripta, 2011)
We present here a Monte Carlo program based on the EGS5 package for modeling the detector response of position-sensitive x-ray detectors. The program is used to estimate the polarimeter quality of two novel detector systems applied in Compton polarimetry. The validity of the underlying physical models is verified by comparing the simulation output to experimental data obtained at the experimental storage ring, ESR.
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Non-hexagonal Large-Pitch Fibers for enhanced mode discrimination - Stutzki, F.; Jansen, F.; Jauregui, C.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2011)
Photonic-Crystal Fibers (PCF) are among the most promising concepts to achieve large mode field areas suitable for the reduction of nonlinearities in fibers. Differential mode propagation loss is the cornerstone of effective single-mode behavior in passive and core-pumped active PCFs. In this work, we explore non-hexagonal PCF designs with increased mode discrimination in comparison to the classical hexagonal PCF designs. It is shown that a pentagonal design can increase the mode discrimination and, simultaneously, also improve the beam quality of Large-Pitch Fibers with mode field diameters well beyond 100 µm.
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Observation of intrashell radiative decay of Li-like uranium (2p_(3/2) - 2s_(1/2)) using silicon drift detectors - Nakano, Y.; Takano, Y.; Shindo, T.; Ikeda, T.; Kanai, Y.; Suda, S.; Azuma, T.; Br{\"{a}uning, H. and Br{\"{a}uning-Demian, A. and St{\"{o}}hlker, T. and Dauvergne, D. and Yamazaki, Y. (Physica Scripta, 2011)
We observed the x-ray emission of 191.7 MeV u^(−1) Li-like uranium associated with resonant coherent excitation from 1s^(2) 2s to 1s^(2) 2p_(3/2) (4459 eV) in a thin silicon crystal target. De-excitation x-rays were observed by using large-area silicon drift detectors installed inside the target vacuum chamber together with their preamplifiers. We found that the x-ray yield under the resonance condition was clearly enhanced by a factor of three compared to that under the random incidence condition.
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Polarization Of The High-Energy End Of The Electron-Nucleus Bremsstrahlung In Electron-Atom Collisions - M{\"{a}rtin, R. and Barday, R. and Jakubassa-Amundsen, D. and Enders, J. and Poltoratska, Y. and Spillmann, U. and Surzhykov, A. and Weber, G. and Yerokhin, V. A. and St{\"{o}}hlker, T. (AIP Conference Proceedings, 2011)
The linear polarization of bremsstrahlung radiation emitted in collisions of spin‐polarized and unpolarized electrons with carbon and gold targets has been measured for an incident kinetic energy of 100 keV. We present preliminary results for the degree of linear polarization for incident unpolarized electrons as a function of bremsstrahlung photon energy.
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SPARC: The Stored Particle Atomic Research Collaboration At FAIR - St{\"{o}}hlker, T.; Beyer, H. F.; Br{\"{a}uning-Demian, A. and Brandau, C. and Gumberidze, A. and Grisenti, R. E. and Hagmann, S. and Herfurth, F. and Kozhuharov, Ch. and K{\"{u}}hl, T. and Liesen, D. and Litvinov, Yu. and M{\"{a}rtin, R. and N{\"{o}}rtersh{\"{a}user, W. and Kester, O. and Petridis, N. and Quint, W. and Schramm, U. and Schuch, R. and Spillmann, U. and Trotsenko, S. and Weber, G. (AIP Conference Proceedings, 2011)
The future international accelerator Facility for Antiproton and Ion Research (FAIR) encompasses 4 scientific pillars containing at this time 14 approved technical proposals worked out by more than 2000 scientists from all over the world. They offer a wide range of new and challenging opportunities for atomic physics research in the realm of highly‐charged heavy ions and exotic nuclei. As one of the backbones of the Atomic, Plasma Physics and Applications (APPA) pillar, the Stored Particle Atomic Physics Research Collaboration (SPARC) has organized tasks and activities in various working groups for which we will present a concise survey on their current status.
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Controlling the Spacing of Attosecond Pulse Trains from Relativistic Surface Plasmas - Behmke, M.; an der Bruegge, D.; R{\"{o}}del, C.; Cerchez, M.; Hemmers, D.; Heyer, M.; J{\"{a}ckel, O. and K{\"{u}}bel, M. and Paulus, G.G. and Pretzler, G. and Pukhov, A. and Toncian, M. and Toncian, T. and Willi, O. (Physical Review Letters, 2011)
When a laser pulse hits a solid surface with relativistic intensities, XUV attosecond pulses are generated in the reflected light. We present an experimental and theoretical study of the temporal properties of attosecond pulse trains in this regime. The recorded harmonic spectra show distinct fine structures which can be explained by a varying temporal pulse spacing that can be controlled by the laser contrast. The pulse spacing is directly related to the cycle-averaged motion of the reflecting surface. Thus the harmonic spectrum contains information on the relativistic plasma dynamics.
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High repetition rate plasma mirror for temporal contrast enhancement of terawatt femtosecond laser pulses by three orders of magnitude - R{\"{o}}del, C.; Heyer, M.; Behmke, M.; K{\"{u}}bel, M.; J{\"{a}ckel, O. and Ziegler, W. and Ehrt, D. and Kaluza, M.C. and Paulus, G.G. (Applied Physics B, 2011)
We present a plasma mirror configuration that improves the temporal pulse contrast of femtosecond terawatt laser pulses by a factor of thousand using a single antireflection coated glass target. The device provides ultra-high contrast for experiments with a maximum repetition rate of 10 Hz. A third-order cross-correlator has been used to measure the temporal pulse contrast for several different plasma mirror targets. It is shown that the ASE can be suppressed to a level of 10^(−11.) A comparison between a triggered and an untriggered plasma mirror reveals differences in the intensity distribution of the focused beam. The triggered plasma mirror produces a slightly larger focus due to the expansion of the triggered plasma mirror at -3 ps before the main pulse. We propose a cost-effective AR-coated and a blank glass target to reduce the costs of the consumable target material. High-harmonic radiation on solid surfaces has been generated with different plasma mirror targets to demonstrate the high laser contrast.
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Hyperfine transitions in He-like ions as a tool for nuclear-spin-dependent parity-nonconservation studies - Ferro, F.; Surzhykov, A.; St{\"{o}}hlker, T. (Physical Review A, 2011)
In this paper a scheme is proposed for measuring nuclear-spin-dependent parity-nonconservation effects in highly charged ions. The idea is to employ circularly polarized laser light for inducing the transition between the level (1s2s)^1S_0 and the hyperfine sublevels of (1s2s)^3S_1 in He-like ions with nonzero nuclear spin. We argue that an interference between the allowed magnetic dipole M1 and the parity-violating electric dipole E1 decay channel leads to an observable asymmetry of order 10^(-7) in the transition cross section, in the atomic range 28 ⩽ Z ⩽ 35. Experimental requirements for asymmetry measurements are discussed in the case of He-like (34)_Se^(77).
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Photon-photon polarization correlations as a tool for studying parity nonconservation in heliumlike uranium - Fratini, F.; Trotsenko, S.; Tashenov, S.; St{\"{o}}hlker, T.; Surzhykov, A. (Physical Review A, 2011)
Due to electron-nucleus weak interaction, atomic bound states with different parities turn out to be mixed. We discuss a prospective method for measuring the mixing parameter between the nearly degenerate metastable states 1s_(1/2) 2s_(1/2):J=0 and 1s_(1/2) 2p_(1/2):J=0 in heliumlike uranium. Our analysis is based on the polarization properties of the photons emitted in the two-photon decays of such states.
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Polarization and anisotropic emission of K-shell radiation from heavy few electron ions - Thorn, D. B.; Gumberidze, A.; Trotsenko, S.; Bana{ś}, D.; Beyer, H.; Bostock, C. J.; Bray, I.; Chen, W.; DuBois, R.; Fontes, C. J.; Fritzsche, S.; Fursa, D. V.; et al. (Canadian Journal of Physics, 2011)
The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion–atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-α radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.
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Laser-excited acoustical phonons probed by ultrashort pulses from a laser-driven x-ray diode - Schulze, K. S.; K{\"{a}mpfer, T. and Uschmann, I. and H{\"{o}}fer, S. and L{\"{o}}tzsch, R. and F{\"{o}}rster, E. (Applied Physics Letters, 2011)
We demonstrate that an ultrashort-pulse laser-driven x-ray diode can be used for time-resolved experiments on a picosecond timescale. Hence, acoustical phonons in germanium are observed after ultrashort laser-excitation and the results are compared with calculations according to a microphysical model. We also show the advantages of this kind of picosecond x-ray source compared to other sources on the basis of its properties.
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Multi-gigawatt ultrashort pulses at high repetition rate and average power from two-stage nonlinear compression - H{\"{a}drich, S. and Carstens, H. and Rothhardt, J. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2011)
We present simple and compact (1.5 m x 0.5 m footprint) post-compression of a state-of-the-art fiber chirped pulse amplification system. By using two stage nonlinear compression in noble gas filled hollow core fibers we shorten 1 mJ, 480 fs, 50 kHz pulses. The first stage is a 53 cm long, 200 µm inner diameter fiber filled with xenon with subsequent compression in a chirped mirror compressor. A 20 cm, 200 µm inner diameter fiber filled with argon further broadens the spectrum in a second stage and compression is achieved with another set of chirped mirrors. The average power is 24.5 W / 19 W after the first / second stage, respectively. Compression to 35 fs is achieved. Numerical simulations, agreeing well with experimental data, yield a peak power of 5.7 GW at a pulse energy of 380 µJ making this an interesting source for high harmonic generation at high repetition rate and average power.
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Preferential gain photonic-crystal fiber for mode stabilization at high average powers - Eidam, T.; H{\"{a}drich, S. and Jansen, F. and Stutzki, F. and Rothhardt, J. and Carstens, H. and Jauregui, C. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2011)
We report on the design and experimental investigation of a preferential gain photonic-crystal fiber with a mode-field diameter of 47 µm. This few-mode fiber design confines the doping of Ytterbium-ions just to the center of the core and, therefore, promotes fundamental mode operation. In a chirped-pulse amplification system we extracted up to 303 W of average power from this fiber with a measured M^2 value of 1.4.
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The FLASH pump-probe laser system: Setup, characterization and optical beamlines - Redlin, H.; Al-Shemmary, A.; Azima, A.; Stojanovic, N.; Tavella, F.; Will, I.; Duesterer, S. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011)
We describe the optical pump–probe laser system at the XUV free-electron laser FLASH at DESY. A growing interest in optical laser pulses combined with the free-electron laser (FEL) beam for time-resolved experiments raise high demands on the stability of operation and knowledge on the status of synchronization between the XUV and optical pulses. In this publication we describe this system, the characterization of the optical pulses, synchronization and timing schemes as well as beamlines that transport beam to experimental stations.
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Collection and focusing of laser accelerated ion beams for therapy applications - Hofmann, I.; Meyer-ter-Vehn, J.; Yan, X.; Orzhekhovskaya, A.; Yaramyshev, S. (Physical Review Special Topics - Accelerators and Beams, 2011)
Experimental results in laser acceleration of protons and ions and theoretical predictions that the currently achieved energies might be raised by factors 5 - 10 in the next few years have stimulated research exploring this new technology for oncology as a compact alternative to conventional synchrotron based accelerator technology. The emphasis of this paper is on collection and focusing of the laser produced particles by using simulation data from a specific laser acceleration model. We present a scaling law for the “chromatic emittance” of the collector - here assumed as a solenoid lens - and apply it to the particle energy and angular spectra of the simulation output. For a 10 Hz laser system we find that particle collection by a solenoid magnet well satisfies requirements of intensity and beam quality as needed for depth scanning irradiation. This includes a sufficiently large safety margin for intensity, whereas a scheme without collection - by using mere aperture collimation - hardly reaches the needed intensities.
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Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia - Saathoff, G.; Reinhardt, S.; Holzwarth, R.; H{\"{a}nsch, T. and Udem, Th. and Bing, D. and Schwalm, D. and Wolf, A. and Karpuk, S. and Huber, G. and Novotny, C. and Botermann, B. and Geppert, C. and N{\"{o}}rtersh{\"{a}user, W. and K{\"{u}}hl, T. and St{\"{o}}hlker, T. and Gwinner, G. (The European Physical Journal C, 2011)
In an article “Lorentz violation in high-energy ions” by S. Devasia published in this Journal [EPJ C 69, 343 (2010)], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an “indication of Lorentz violation”. We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity.
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Few-femtosecond timing at fourth-generation X-ray light sources - Tavella, F.; Stojanovic, N.; Geloni, G.; Gensch, M. (Nature Photonics, 2011)
Fourth-generation X-ray light sources are being developed to deliver laser-like X-ray pulses at intensities and/or repetition rates that are beyond the reach of table-top devices. An important class of experiments at these new facilities comprises pump–probe experiments, which are designed to investigate chemical reactions and processes occurring on the molecular or even atomic level, and on the timescale of a few femtoseconds. Good progress has been made towards the generation of ultrashort X-ray pulses (for example, at FLASH or LCLS), but experiments suffer from the intrinsic timing jitter between the X-ray pulses and external laser sources3. In this Letter, we present a new approach that provides few-femtosecond temporal resolution. Our method uses coherent terahertz radiation generated at the end of the X-ray undulator by the same electron bunch that emits the X-ray pulse. It can therefore be applied at any advanced light source working with ultrashort electron bunches and undulators.
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High average power large-pitch fiber amplifier with robust single-mode operation - Stutzki, F.; Jansen, F.; Eidam, T.; Steinmetz, A.; Jauregui, C.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2011)
Ytterbium-doped large-pitch fibers with very large mode areas are investigated in a high-power fiber amplifier configuration. An average output power of 294 W is demonstrated, while maintaining robust single-mode operation with a mode field diameter of 62 µm. Compared to previous active large-mode area designs, the threshold of mode instabilities is increased by a factor of about 3.
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Ultrafast fiber lasers for strong-field physics experiments - Limpert, J.; H{\"{a}drich, S. and Rothhardt, J. and Krebs, M. and Eidam, T. and Schreiber, T. and T{\"{u}}nnermann, A. (Laser { &} Photonics Reviews, 2011)
The recent demonstration of rare-earth-doped fiber lasers with a continuous-wave output power approaching the 10-kW level with diffraction-limited beam quality proves that fiber lasers constitute a scalable solid-state laser concept in terms of average power. In order to generate high peak power pulses from a fiber several fundamental limitations have to be overcome. This can be achieved by novel experimental strategies and fiber designs that offer an enormous potential towards ultrafast laser systems combining high average powers (> kW) and high peak power (> GW). In this paper the challenges, achievements and perspectives of ultrashort pulse generation and amplification in fibers are reviewed. This kind of laser system will have a tremendous impact on strong-field physics experiments, such as the generation of coherent light by high-harmonic generation. So far, applications in the interesting EUV spectral range suffer from the very low photon count leading to nonrelevant integration times with highly sophisticated detection schemes. High repetition rate high average power fiber lasers can potentially solve this issue. First demonstrations of high repetition-rate strong-field physics experiments using novel fiber laser systems will be discussed.
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135 W average-power femtosecond pulses at 520 nm from a frequency-doubled fiber laser system - Rothhardt, J.; Eidam, T.; H{\"{a}drich, S. and Jansen, F. and Stutzki, F. and Gottschall, T. and Andersen, T. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Letters, 2011)
We present a high-average-power femtosecond laser system at 520 nm central wavelength. The laser system delivers sub- 500 fs pulses with 135 W average power at a pulse repetition rate of 5.25 MHz. Excellent beam quality is provided by high power fiber amplifiers and maintained during frequency doubling, resulting in a beam quality factor of M^2 < 1.2. To our knowledge, the system presented here is the highest average power green laser source generating femtosecond pulses with diffraction-limited beam quality.
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Coherently combined fiber laser system delivering 120 mu J femtosecond pulses - Seise, E.; Klenke, A.; Breitkopf, S.; Pl{\"{o}}tner, M.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2011)
We report on the coherent combination of two chirped pulsed fiber lasers. The beams coming from two 100 μm core diameter ytterbium-doped rod-type fibers were coupled in a Mach-Zehnder-type interferometer by means of a polarization beam splitter. Active stabilization of the interferometer was achieved by using a piezo-mounted mirror driven by a H{\"{a}nsch-Couillaud polarization detection system. Pulses with 120 μJ energy and a compressed duration of 800 fs were obtained. This, compared with the 66 μJ coming from each single amplifier, results in a combining efficiency as high as 91%.
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Determination of high-purity polarization state of X-rays - Marx, B.; Uschmann, I.; H{\"{o}}fer, S.; L{\"{o}}tzsch, R.; Wehrhan, O.; F{\"{o}}rster, E.; Kaluza, M.C.; St{\"{o}}hlker, T.; Gies, H.; Detlefs, C.; Roth, T.; H{\"{a}rtwig, J. and Paulus, G.G. (Optics Communications, 2011)
We report on the measurement of the highest purity of polarization of X-rays to date. The measurements are performed by combining a brilliant undulator source with an X-ray polarimeter. The polarimeter is composed of a polarizer and an analyzer, each based on four reflections at channel-cut crystals with a Bragg angle very close to 45°. Experiments were performed at three different X-ray energies, using different Bragg reflections: Si(400) at 6457.0 eV, Si(444) at 11,183.8 eV, and Si(800) at 12,914.0 eV. At 6 keV a polarization purity of 1.5 × 10^-9 is achieved. This is an improvement by more than two orders of magnitude as compared to previously reported values. The polarization purity decreases slightly for shorter X-ray wavelengths. The sensitivity of the polarimeter is discussed with respect to a proposed experiment that aims at the detection of the birefringence of vacuum induced by super-strong laser fields.
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High power narrow-band fiber-based ASE source - Schmidt, O.; Rekas, M.; Wirth, C.; Rothhardt, J.; Rhein, S.; Kliner, A.; Strecker, M.; Schreiber, T.; Limpert, J.; Eberhardt, R.; T{\"{u}}nnermann, A. (Optics Express, 2011)
In this paper we describe a high power narrow-band amplified spontaneous emission (ASE) light source at 1030 nm center wavelength generated in an Yb-doped fiber-based experimental setup. By cutting a small region out of a broadband ASE spectrum using two fiber Bragg gratings a strongly constrained bandwidth of 12±2 pm (3.5±0.6 GHz) is formed. A two-stage high power fiber amplifier system is used to boost the output power up to 697 W with a measured beam quality of M2≤1.34. In an additional experiment we demonstrate a stimulated Brillouin scattering (SBS) suppression of at least 17 dB (theoretically predicted 20 dB), which is only limited by the dynamic range of the measurement and not by the onset of SBS when using the described light source. The presented narrow-band ASE source could be of great interest for brightness scaling applications by beam combination, where SBS is known as a limiting factor.
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High-repetition-rate sub-5-fs pulses with 12 GW peak power from fiber-amplifier-pumped optical parametric chirped-pulse amplification - H{\"{a}drich, S. and Demmler, S. and Rothhardt, J. and Jocher, C. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Letters, 2011)
An optical parametric chirped-pulse amplification system delivering pulses with more than 12 GW peak power is presented. Compression to sub- 5 fs, 87 μJ and 5.4 fs, 100 μJ is realized at the 30 kHz repetition rate. A high-energy fiber chirped-pulse amplification system operating at 1 mJ pulse energy and nearly transform-limited pulses is used to achieve ultrabroadband amplification in two 2mm beta-barium borate crystals. Precise pulse shaping is used to compress the pulses to a few percentages of their transform limit. Assuming diffraction limited focusing (d < 2 μm), peak intensities as high as 10^(18) W/cm2 can be reached.
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Real-time pulse length measurement of few-cycle laser pulses using above-threshold ionization - Sayler, A. M.; Rathje, T.; M{\"{u}}ller, W.; K{\"{u}}rbis, C.; R{\"{u}}hle, K.; Stibenz, G.; Paulus, G.G. (Optics Express, 2011)
The pulse lengths of intense few-cycle (4 - 10 fs) laser pulses at 790 nm are determined in real-time using a stereographic above-threshold ionization (ATI) measurement of Xe, i.e. the same apparatus recently shown to provide a precise, real-time, every-single-shot, carrier-envelope phase measurement of ultrashort laser pulses. The pulse length is calibrated using spectral-phase interferometry for direct electric-field reconstruction (SPIDER) and roughly agrees with calculations done using quantitative rescattering theory (QRS). This stereo-ATI technique provides the information necessary to characterize the waveform of every pulse in a kHz pulse train, within the Gaussian pulse approximation, and relies upon no theoretical assumptions. Moreover, the real-time display is a highly effective tool for tuning and monitoring ultrashort pulse characteristics.
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Spectral distribution of the 2S → 1S two-photon transition in atoms and few-electron ions - Kumar, A.; Trotsenko, S.; Volotka, A. V.; Bana{ś}, D.; Beyer, H. F.; Br{\"{a}uning, H. and Fritzsche, S. and Gumberidze, A. and Hagmann, S. and Hess, S. and Kozhuharov, C. and Reuschl, R. and Spillmann, U. and Trassinelli, M. and Weber, G. and St{\"{o}}hlker, T. (Pramana - Journal of Physics, 2011)
The two-photon decay of the 2S state to the ground state in dressed atoms and one- or two-electron ions has been studied for several decades. Relativistic calculations have shown an Z-dependence of the spectral shape of this two-photon transition in one- or two-electron ions. We have measured the spectral distribution of the 1s2s 1^S_0 → 1s2 1^S_0 two-photon transition in He-like tin at the ESR storage ring using a new approach for such experiments. In this method, relativistic collisions of initially Li-like projectiles with a gaseous target were used to populate exclusively the first excited state, 1s2s, of He-like tin, which provided a clean two-photon spectrum. The measured two-photon spectral distribution was compared with fully relativistic calculations. The obtained results show very good agreement with the calculations for He-like tin.
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Dark current measurements on a superconducting cavity using a cryogenic current comparator - Geithner, R.; Neubert, R.; Vodel, W.; Seidel, P.; Knaack, K.; Vilcins, S.; Wittenburg, K.; Kugeler, O.; Knobloch, J. (Review of Scientific Instruments, 2011)
his paper presents nondestructive dark current measurements of tera electron volt energy superconducting linear accelerator cavities. The measurements were carried out in an extremely noisy accelerator environment using a low temperature dc superconducting quantum interference device based cryogenic current comparator. The overall current sensitivity under these rough conditions was measured to be 0.2 nA/Hz^1/2, which enables the detection of dark currents of 5 nA.
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Fiber chirped-pulse amplification system emitting 3.8 GW peak power - Eidam, T.; Rothhardt, J.; Stutzki, F.; Jansen, F.; H{\"{a}drich, S. and Carstens, H. and Jauregui, C. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2011)
We report on the experimental demonstration of a fiber chirped- pulse amplification system capable of generating nearly transform-limited sub 500 fs pulses with 2.2 mJ pulse energy at 11 W average power. The resulting record peak power of 3.8 GW could be achieved by combining active phase shaping with an efficient reduction of the acquired nonlinear phase. Therefore, we used an Ytterbium-doped large-pitch fiber with a mode field diameter of 105 µm as the main amplifier.
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High average and peak power femtosecond large-pitch photonic-crystal-fiber laser - Baumgartl, M.; Jansen, F.; Stutzki, F.; Jauregui, C.; Ortac, B.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2011)
We report on the generation of high-average-power and high-peak-power ultrashort pulses from a mode-locked fiber laser operating in the all-normal-dispersion regime. As gain medium, a large-mode-area ytterbium-doped large-pitch photonic-crystal fiber is used. The self-starting fiber laser delivers 27 W of average power at 50.57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub - 100 fs , leading to pulse peak powers as high as 3.2 MW.
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Hyperfine interaction effects on the (1s2p)P-3(1)-(1s2s)S-1(0) energy splitting in He-like ions for parity nonconservation studies - Ferro, F.; Artemyev, A.; Surzhykov, A.; St{\"{o}}hlker, T. (Canadian Journal of Physics, 2011)
Accurate theoretical knowledge of the (1s2p)^3P_1–(1s2s)^1S_0 splitting in He-like ions is demanded for future experimental studies of the nuclear spin-dependent part of the weak interaction. In this paper we perform a calculation of the hyperfine structure of (1s2p)^3P_1–(1s2s)^1S_0 within 3 ≤ Z ≤ 35, Z being the atomic number. In this Z range parity nonconservation (PNC) effects are amplified by the close energy proximity of the opposite parity levels (1s2p)^3P_1 and (1s2s)^1S_0. We find that the hyperfine structure is relevant for Z > 12, and produces splitting among the hyperfine sublevels as large as 150 meV for medium Z He-like ions (Z 35).
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Isotope-shift measurements of stable and short-lived lithium isotopes for nuclear-charge-radii determination - N{\"{o}}rtersh{\"{a}user, W. and Sanchez, R. and Ewald, G. and Dax, A. and Behr, J. and Bricault, P. and Bushaw, B. A. and Dilling, J. and Dombsky, M. and Drake, G. W. F. and G{\"{o}}tte, S. and Kluge, H.-J. and K{\"{u}}hl, T. and Lassen, J. and Levy, C. D. P. and Pachucki, K. and Pearson, M. and Puchalski, M. and Wojtaszek, A. and Yan, Z.-C. and Zimmermann, C. (Physical Review A, 2011)
Changes in the mean square nuclear charge radii along the lithium isotopic chain were determined using a combination of precise isotope shift measurements and theoretical atomic structure calculations. Nuclear charge radii of light elements are of high interest due to the appearance of the nuclear halo phenomenon in this region of the nuclear chart. During the past years we have developed a laser spectroscopic approach to determine the charge radii of lithium isotopes which combines high sensitivity, speed, and accuracy to measure the extremely small field shift of an 8-ms-lifetime isotope with production rates on the order of only 10 000 atoms/s. The method was applied to all bound isotopes of lithium including the two-neutron halo isotope 11^Li at the on-line isotope separators at GSI, Darmstadt, Germany, and at TRIUMF, Vancouver, Canada. We describe the laser spectroscopic method in detail, present updated and improved values from theory and experiment, and discuss the results.
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Precise, real-time, every-single-shot, carrier-envelope phase measurement of ultrashort laser pulses - Sayler, A. M.; Rathje, T.; M{\"{u}}ller, W.; R{\"{u}}hle, K.; Kienberger, R.; Paulus, G.G. (Optics Letters, 2011)
In this Letter we demonstrate a method for real-time determination of the carrier-envelope phase of each and every single ultrashort laser pulse at kilohertz repetition rates. The technique expands upon the recent work of Wittmann and incorporates a stereographic above-threshold laser-induced ionization measurement and electronics optimized to produce a signal corresponding to the carrier-envelope phase within microseconds of the laser interaction, thereby facilitating data-tagging and feedback applications. We achieve a precision of 113 mrad (6.5°) over the entire 2π range.
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Preparatory measurements for a test of time dilation in the ESR - Botermann, B.; Novotny, C.; Bing, D.; Geppert, C.; Gwinner, G.; H{\"{a}nsch, T. W. and Huber, G. and Karpuk, S. and K{\"{u}}hl, T. and N{\"{o}}rtersh{\"{a}user, W. and Reinhardt, S. and Saathoff, G. and Schwalm, D. and St{\"{o}}hlker, T. and Wolf, A. (Canadian Journal of Physics, 2011)
We present preparatory measurements for an improved test of time dilation at the experimental storage ring (ESR) at GSI in Darmstadt. A unique combination of particle accelerator experiments and laser spectroscopy is used to perform this test with the highest precision. 7^Li+ ions are accelerated to 34% of the speed of light at the GSI Helmholtzzentrum f{\"{u}}r Schwerionenforschung and stored in the experimental storage ring. The forward and backward Doppler shifts of an electric dipole transition of these ions are measured with laser spectroscopy techniques. From these Doppler shifts, both the ion velocity β = ν/c and the time dilation factor can be derived for testing Special Relativity. Two laser systems have been developed to drive the 3^S_1 → 3^P_2 transition in 7^Li+. Moreover, a detector system composed of photomultipliers, both to monitor the exact laser ion beam overlap as well as to optimize fluorescence detection, has been set up and tested. We investigate optical-optical double-resonance spectroscopy on a closed Λ-type three-level system to overcome Doppler broadening. A residual, broadened fluorescence background caused by velocity-changing processes in the ion beam is identified, and a background subtraction scheme implemented. At the present stage the experimental sensitivity, although already comparable with previous measurements on slower ion beams at the TSR storage ring that led to < 8.4 × 10^–8, suffer from a poor signal-to-noise ratio. Modifications of the ion source as well as the detection system are discussed that promise to improve the sensitivity by one order of magnitude.
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Refluxing of fast electrons in solid targets irradiated by intense, picosecond laser pulses - Quinn, M. N.; Yuan, X. H.; Lin, X. X.; Carroll, D. C.; Tresca, O.; Gray, R. J.; Coury, M.; Li, C.; Li, Y. T.; Brenner, C. M.; Robinson, A. P. L.; Neely, D.; et al. (Plasma Physics and Controlled Fusion, 2011)
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.
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Role of resistivity gradient in laser-driven ion acceleration - Gizzi, L. A.; Betti, S.; F{\"{o}}rster, E.; Giulietti, D.; H{\"{o}}fer, S.; K{\"{o}}ster, P.; Labate, L.; L{\"{o}}tzsch, R.; Robinson, A. P. L.; Uschmann, I. (Physical Review Special Topics - Accelerators and Beams, 2011)
It was predicted that, when a fast electron beam with some angular spread is normally incident on a resistivity gradient, magnetic field generation can occur that can inhibit beam propagation [A. R. Bell et al. Phys. Rev. E 58 2471 (1998)]. This effect can have consequences on the laser-driven ion acceleration. In the experiment reported here, we compare ion emission from laser irradiated coated and uncoated metal foils and we show that the ion beam from the coated target has a much smaller angular spread. Detailed hybrid numerical simulations confirm that the inhibition of fast electron transport through the resistivity gradient may explain the observed effect.
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Single-shot carrier-envelope-phase-tagged ion-momentum imaging of nonsequential double ionization of argon in intense 4-fs laser fields - Johnson, N.; Herrwerth, O.; Wirth, A.; De, S.; Ben-Itzhak, I.; Lezius, M.; Bergues, B.; Kling, M. F.; Senftleben, A.; Schr{\"{o}}ter, C. D.; Moshammer, R.; Ullrich, J.; et al. (Physical Review A, 2011)
Single-shot carrier-envelope-phase (CEP) tagging is combined with a reaction mircoscope (REMI) to investigate CEP-dependent processes in atoms. Excellent experimental stability and data acquisition longevity are achieved. Using this approach, we study the CEP effects for nonsequential double ionization of argon in 4-fs laser fields at 750 nm and an intensity of 1.6 × 10^14 W/cm2. The Ar^(2+) ionization yield shows a pronounced CEP dependence which compares well with recent theoretical predictions employing quantitative rescattering theory [S. Micheau et al. Phys. Rev. A 79 013417 (2009)]. Furthermore, we find strong CEP influences on the Ar^(2+) momentum spectra along the laser polarization axis.
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Coherent addition of fiber-amplified ultrashort laser pulses - Seise, E.; Klenke, A.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Express, 2010)
We report on a novel approach of performance scaling of ultrafast lasers by means of coherent combination. Pulses from a single mode-locked laser are distributed to a number of spatially separated fiber amplifiers and coherently combined after amplification. Splitting and combination is achieved by polarization cubes, i.e. the approach bases on polarization combining. A H{\"{a}nsch-Couillaud detector measures the polarization state at the output. The error signal (deviation from linear polarization) is used to stabilize the synchronization of different channels. In a proof-of-principle experiment the combination of two femtosecond fiber-based CPA systems is presented. A combining efficiency as high as 97% has been achieved. The technique offers a unique scaling potential and can be applied to all ultrafast amplification schemes independent of the architecture of the gain medium.
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Direct Determination of the Magnetic Quadrupole Contribution to the Lyman-alpha(1) Transition in a Hydrogenlike Ion - Weber, G.; Br{\"{a}uning, H. and Surzhykov, A. and Brandau, C. and Fritzsche, S. and Geyer, S. and Hagmann, S. and Hess, S. and Kozhuharov, C. and M{\"{a}rtin, R. and Petridis, N. and Reuschl, R. and Spillmann, U. and Trotsenko, S. and Winters, D. F. A. and St{\"{o}}hlker, T. (Physical Review Letters, 2010)
We report the observation of an interference between the electric dipole (E1) and the magnetic quadrupole (M2) amplitudes for the linear polarization of the Ly-alpha(1) (2p(3/2) -> 1s(1/2)) radiation of hydrogenlike uranium. This multipole mixing arises from the coupling of the ion to different multipole components of the radiation field. Our observation indicates a significant depolarization of the Ly-alpha(1) radiation due to the E1-M2 amplitude mixing. It proves that a combined measurement of the linear polarization and of the angular distribution enables a very precise determination of the ratio of the E1 and the M2 transition amplitudes and the corresponding transition rates without any assumptions concerning the population mechanism for the 2p(3/2) state.
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Finite basis set approach to the two-centre Dirac problem in Cassini coordinates - Artemyev, A. N.; Surzhykov, A.; Indelicato, P.; Plunien, G.; St{\"{o}}hlker, T. (Journal of Physics B, 2010)
We lay out a new approach to solving the two-centre Dirac eigenvalue problem. It is based on the application of B-spline basis sets constructed in Cassini coordinates. The approach provides a very promising way for the theoretical description of various atomic processes such as charge transfer, excitation, ionization and electron-positron pair production that accompany slow collisions of heavy ions. Moreover, yielding a (quasi-) complete set of eigensolutions, the finite basis set method allows a systematic analysis of the quantum electrodynamics (QED) corrections to the energy levels of heavy quasi-molecules formed in these collisions.
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Reply to 'The super-quadratic growth of high-harmonic signal as a function of pressure' - Seres, J.; Seres, E.; Ecker, B.; Hochhaus, D.; Zimmer, D.; Bagnoud, V.; Aurand, B.; Zielbauer, B.; Spielmann, C.; K{\"{u}}hl, T. (Nature Physics, 2010)
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).
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Schwinger pair production in space- and time-dependent electric fields: Relating the Wigner formalism to quantum kinetic theory - Hebenstreit, F.; Alkofer, R.; Gies, H. (Physical Review D, 2010)
The nonperturbative electron-positron pair production (Schwinger effect) is considered for space- and time-dependent electric fields E(x,t). Based on the Dirac-Heisenberg-Wigner formalism, we derive a system of partial differential equations of infinite order for the 16 irreducible components of the Wigner function. In the limit of spatially homogeneous fields the Vlasov equation of quantum kinetic theory is rediscovered. It is shown that the quantum kinetic formalism can be exactly solved in the case of a constant electric field E(t)=E_0 and the Sauter-type electric field E(t)=E_0 sech^2 (t/τ). These analytic solutions translate into corresponding expressions within the Dirac-Heisenberg-Wigner formalism and allow to discuss the effect of higher derivatives. We observe that spatial field variations typically exert a strong influence on the components of the Wigner function for large momenta or for late times.
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A cascaded laser acceleration scheme for the generation of spectrally controlled proton beams - Pfotenhauer, S. M.; J{\"{a}ckel, O. and Polz, J. and Steinke, S. and Schlenvoigt, H. and Heymann, J. and Robinson, A. P. L. and Kaluza, M.C. (New Journal of Physics, 2010)
We present a novel, cascaded acceleration scheme for the generation of spectrally controlled ion beams using a laser-based accelerator in a 'double-stage' setup. An MeV proton beam produced during a relativistic laser-plasma interaction on a thin foil target is spectrally shaped by a secondary laser-plasma interaction on a separate foil, reliably creating well-separated quasi-monoenergetic features in the energy spectrum. The observed modulations are fully explained by a one-dimensional (1D) model supported by numerical simulations. These findings demonstrate that laser acceleration can, in principle, be applied in an additive manner.
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All-optical measurement of the hot electron sheath driving laser ion acceleration from thin foils - J{\"{a}ckel, O. and Polz, J. and Pfotenhauer, S. M. and Schlenvoigt, H. and Schw{\"{o}}rer, H. and Kaluza, M.C. (New Journal of Physics, 2010)
We present experimental results from an all-optical diagnostic method to directly measure the evolution of the hot-electron distribution driving the acceleration of ions from thin foils using high-intensity lasers. Central parameters of laser ion acceleration such as the hot-electron density, the temperature distribution and the conversion efficiency from laser pulse energy into hot electrons become comprehensively accessible with this technique.
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Axion-like-particle search with high-intensity lasers - D{\"{o}}brich, B.; Gies, H. (Journal of High Energy Physics, 2010)
We study ALP-photon-conversion within strong inhomogeneous electromagnetic fields as provided by contemporary high-intensity laser systems. We observe that probe photons traversing the focal spot of a superposition of Gaussian beams of a single high-intensity laser at fundamental and frequency-doubled mode can experience a frequency shift due to their intermittent propagation as axion-like-particles. This process is strongly peaked for resonant masses on the order of the involved laser frequencies. Purely laser-based experiments in optical setups are sensitive to ALPs in the eV mass range and can thus complement ALP searches at dipole magnets.
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Optimization of high performance ultrafast fiber laser systems to > 10 GW peak power - Schimpf, D. N.; Limpert, J.; T{\"{u}}nnermann, A. (Journal of the Optical Society of America B, 2010)
We show that the peak powers of ytterbium-doped fiber chirped pulse amplification (CPA) can be scaled by at least 1 order of magnitude (in the transform limit) as compared to current systems by using a different spectral region of operation. A simple and fast model for saturated broadband fiber CPA systems is developed and applied to study the impact of the interplay between the spectrally dependent small signal gain and the saturation on the output bandwidth. The influence of self-phase modulation on the recompression of the pulse is discussed. It can be shown that the novel operation regime exhibits superior performance even if nonlinear effects are considered. The numerical results are significant for the design of the next generation of ultrafast high power fiber lasers.
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Relativistic calculations of the charge-transfer probabilities and cross sections for low-energy collisions of H-like ions with bare nuclei - Tupitsyn, I. I.; Kozhedub, Y. S.; Shabaev, V. M.; Deyneka, G. B.; Hagmann, S.; Kozhuharov, C.; Plunien, G.; St{\"{o}}hlker, T. (Physical Review A, 2010)
A method for solving the time-dependent two-center Dirac equation is developed. The time-dependent Dirac wave function is represented as a sum of atomiclike Dirac-Sturm orbitals, localized at the ions. The atomic orbitals are generated by solving numerically the one-center Dirac and Dirac-Sturm equations by means of a finite-difference approach with the Coulomb potential taken as the sum of the exact reference-nucleus potential and of the other nucleus within the monopole approximation. An original procedure for calculating the two-center integrals with these orbitals is proposed. As a first test of the approach developed here, calculations of the charge-transfer and ionization cross sections for the H(1s)-proton collisions at proton energies from 1 to 100 keV are performed. The obtained results are compared with related experimental and other theoretical data. To investigate the role of the relativistic effects, the charge-transfer cross sections in collisions of Ne9+(1s)-Ne10+ (at energies from 0.1 to 10 MeV/u) and U91+(1s)-U92+ (at energies from 6 to 10 MeV/u) are calculated for both relativistic and nonrelativistic cases.
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Spectroscopy of betatron radiation emitted from laser-produced wakefield accelerated electrons - Thorn, D. B.; Geddes, C. G. R.; Matlis, N. H.; Plateau, G. R.; Esarey, E. H.; Battaglia, M.; Schr{\"{o}}der, C. B.; Shiraishi, S.; St{\"{o}}hlker, T.; Toth, C.; Leemans, W. P. (Review of Scientific Instruments, 2010)
X-ray betatron radiation is produced by oscillations of electrons in the intense focusing field of a laser-plasma accelerator. These hard x-rays show promise for use in femtosecond-scale time-resolved radiography of ultrafast processes. However, the spectral characteristics of betatron radiation have only been inferred from filter pack measurements. In order to achieve higher resolution spectral information about the betatron emission, we used an x-ray charge-coupled device to record the spectrum of betatron radiation, with a full width at half maximum resolution of 225 eV. In addition, we have recorded simultaneous electron and x-ray spectra along with x-ray images that allow for a determination of the betatron emission source size, as well as differences in the x-ray spectra as a function of the energy spectrum of accelerated electrons.
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Temporal pulse control of a multi-10 TW diode-pumped Yb:Glass laser - Hornung, M.; B{\"{o}}defeld, R.; Siebold, M.; Kessler, A.; Schnepp, M.; Wachs, R.; S{\"{a}vert, A. and Podleska, S. and Keppler, S. and Hein, J. and Kaluza, M.C. (Applied Physics B, 2010)
At the Institute of Optics and Quantum Electronics in Jena, Germany, the currently most powerful diode-pumped solid-state laser system with 25-TW peak power Polaris is in operation. In this paper we give an overview about the dispersion management of the chirped pulse amplification in order to minimize the pulse duration and thus to maximize the intensity available for experiments. A detailed description of the stretcher and compressor design with a novel alignment routine is given as well as measurements for the pulse duration and the temporal contrast. The far field measurement of the beam focussed by an off-axis parabola yields a nearly diffraction limited focal spot.
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The role of hot electron refluxing in laser-generated K-alpha sources - Neumayer, P.; Aurand, B.; Basko, M.; Ecker, B.; Gibbon, P.; Hochhaus, D. C.; Karmakar, A.; Kazakov, E.; K{\"{u}}hl, T.; Labaune, C.; Rosmej, O.; Tauschwitz, An.; et al. (Physics of Plasmas, 2010)
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.
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Electron capture in intermediate-to-fast heavy ion collisions with neutral atoms - Shevelko, V. P.; St{\"{o}}hlker, T.; Tawara, H.; Tolstikhina, I. Yu.; Weber, G. (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010)
Electron capture processes of heavy ions, like Ge(q+), Xe(q+). Pb(q+), and U(q+), respectively, with the charge q approximate to 10-40, occurring in collisions with gaseous targets are considered in the E = 0.1-100 MeV/u projectile energy range. Calculations of single-electron capture cross sections are performed using the CDW and the CAPTURE computer codes These are compared with available experimental data and CTMC (Classical-Trajectory Monte Carlo) calculations. Although the overall agreement is found to be within a factor of two, In some cases of heavy many-electron projectiles, e g. U(28+) + N(2), Ar collisions, experimental cross sections at high energies are far smaller than theoretical predictions Moreover, for these collision systems the observed energy dependencies are quite different from each other. Possible reasons for this behavior and how the theoretical models can be improved are discussed.
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High harmonic generation by novel fiber amplifier based sources - H{\"{a}drich, S. and Rothhardt, J. and Krebs, M. and Tavella, F. and Willner, A. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2010)
Significant progress in high repetition rate ultrashort pulse sources based on fiber technology is presented. These systems enable operation at a high repetition rate of up to 500 kHz and high average power in the extreme ultraviolet wavelength range via high harmonic generation in a gas jet. High average power few-cycle pulses of a fiber amplifier pumped optical parametric chirped pulse amplifier are used to produce µW level average power for the strongest harmonic at 42.9 nm at a repetition rate of 96 kHz.
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Measurement of Magnetic-Field Structures in a Laser-Wakefield Accelerator - Kaluza, M.C.; Schlenvoigt, H.-P.; Mangles, S. P. D.; Thomas, A. G. R.; Dangor, A. E.; Schw{\"{o}}rer, H.; Mori, W. B.; Najmudin, Z.; Krushelnick, K. M. (Physical Review Letters, 2010)
Experimental measurements of magnetic fields generated in the cavity of a self-injecting laser-wakefield accelerator are presented. Faraday rotation is used to determine the existence of multimegagauss fields, constrained to a transverse dimension comparable to the plasma wavelength similar to lambda(p) and several lambda(p) longitudinally. The fields are generated rapidly and move with the driving laser. In our experiment, the appearance of the magnetic fields is correlated with the production of relativistic electrons, indicating that they are inherently tied to the growth and wave breaking of the nonlinear plasma wave. This evolution is confirmed by numerical simulations, showing that these measurements provide insight into the wakefield evolution with high spatial and temporal resolution.
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Tuning the high-order harmonic lines of a Nd:Glass laser for soft X-ray laser seeding - Hochhaus, D. C.; Seres, J.; Aurand, B.; Ecker, B.; Zielbauer, B.; Zimmer, D.; Spielmann, C.; K{\"{u}}hl, T. (Applied Physics B, 2010)
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.
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Isotopic tuning of the 2 3P0−2 1S0 and 2 3P1−2 1S0 transition energies in He-like ions for future parity-nonconservation experiments - Ferro, F.; Artemyev, A.; St{\"{o}}hlker, T.; Surzhykov, A. (Journal of Instrumentation, 2010)
Crossings of opposite-parity levels in He-like ions for particular values of the atomic number Z offer excellent conditions for precise experimental tests of parity-nonconservation (PNC). Such tests may be performed by inducing, through intense lasers, transitions that are only allowed in presence of PNC. Several spectroscopy experiments have been proposed in the past, but only now, with the advent of high-intensity laser facilities (e.g. PHELIX at GSI or POLARIS at Jena), their feasibility is within reach. In this paper, we use relativistic many-body perturbation theory (RMBPT) to calculate accurately the crossing conditions of the excited levels (1s2s) 1S0 and (1s2p) 3P0 and of (1s2s) 1S0 and (1s2p) 3P1 in intermediate and heavy He-like ions. Moreover, we show the dependence of the energy splittings upon the choice of the nuclear isotope.
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Observation of a Long-Wavelength Hosing Modulation of a High-Intensity Laser Pulse in Underdense Plasma - Kaluza, M.C.; Mangles, S. P. D.; Thomas, A. G. R.; Najmudin, Z.; Dangor, A. E.; Murphy, C. D.; Collier, J. L.; Divall, E. J.; Foster, P. S.; Hooker, C. J.; Langley, A. J.; Smith, J.; et al. (Physical Review Letters, 2010)
We report the first experimental observation of a long-wavelength hosing modulation of a high-intensity laser pulse. Side-view images of the scattered optical radiation at the fundamental wavelength of the laser reveal a transverse oscillation of the laser pulse during its propagation through underdense plasma. The wavelength of the oscillation lambda(hosing) depends on the background plasma density n(e) and scales as lambda(hosing) similar to n(e)(-3/2). Comparisons with an analytical model and two-dimensional particle-in-cell simulations reveal that this laser hosing can be induced by a spatiotemporal asymmetry of the intensity distribution in the laser focus which can be caused by a misalignment of the parabolic focusing mirror or of the diffraction gratings in the pulse compressor.
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Commissioning and early experiments of the PHELIX facility - Bagnoud, V.; Aurand, B.; Blazevic, A.; Borneis, S.; Bruske, C.; Ecker, B.; Eisenbarth, U.; Fils, J.; Frank, A.; Gaul, E.; G{\"{o}}tte, S.; H{\"{a}fner, C. and Hahn, T. and Harres, K. and Heuck, H.-M. and Hochhaus, D. and Hoffmann, D. H. H. and Javorkova, D. and Kluge, H.-J. and K{\"{u}}hl, T. and Kunzer, S. and Kreutz, M. and Merz-Mantwill, T. and Neumayer, P. and Onkels, E. and Reemts, D. and Rosmej, O. and Roth, M. and St{\"{o}}hlker, T. and Tauschwitz, A. and Zielbauer, B. and Zimmer, D. and Witte, K. (Applied Physics B, 2010)
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.
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Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions - Bellei, C.; Nagel, S. R.; Kar, S.; Henig, A.; Kneip, S.; Palmer, C.; S{\"{a}vert, A. and Willingale, L. and Carroll, D. and Dromey, B. and Green, J. S. and Markey, K. and Simpson, P. and Clarke, R. J. and Lowe, H. and Neely, D. and Spindloe, C. and Tolley, M. and Kaluza, M.C. and Mangles, S. P. D. and McKenna, P. and Norreys, P. A. and Schreiber, J. and Zepf, M. and Davies, J. R. and Krushelnick, K. and Najmudin, Z. (New Journal of Physics, 2010)
The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of mu m-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given.
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Performance of a position sensitive Si(Li) x-ray detector dedicated to Compton polarimetry of stored and trapped highly-charged ions - Weber, G.; Br{\"{a}uning, H. and Hess, S. and M{\"{a}rtin, R. and Spillmann, U. and St{\"{o}}hlker, T. (Journal of Instrumentation, 2010)
We report on a novel two-dimensional position sensitive Si(Li) detector dedicated to Compton polarimetry of x-ray radiation arising from highly-charged ions. The performance of the detector system was evaluated in ion-atom collision experiments at the ESR storage ringe at GSI, Darmstadt. Based on the data obtained, the polarimeter efficiency is estimated in this work.
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Short-wavelength soft-x-ray laser pumped in double-pulse single-beam non-normal incidence - Zimmer, D.; Ros, D.; Guilbaud, O.; Habib, J.; Kazamias, S.; Zielbauer, B.; Bagnoud, V.; Ecker, B.; Hochhaus, D. C.; Aurand, B.; Neumayer, P.; K{\"{u}}hl, T. (Physical Review A, 2010)
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.
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Sub-80 fs dissipative soliton large-mode-area fiber laser - Baumgartl, M.; Ortac, B.; Lecaplain, C.; Hideur, A.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2010)
We report on high-energy ultrashort pulse generation from an all-normal-dispersion large-mode-area fiber laser by exploiting an efficient combination of nonlinear polarization evolution (NPE) and a semiconductor-based saturable absorber mode-locking mechanism. The watt-level laser directly emits chirped pulses with a duration of 1 ps and 163 nJ of pulse energy. These can be compressed to 77 fs, generating megawatt-level peak power. Intracavity dynamics are discussed by numerical simulation, and the intracavity pulse evolution reveals that NPE plays a key role in pulse shaping.
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High average and peak power few-cycle laser pulses delivered by fiber pumped OPCPA system - Rothhardt, J.; H{\"{a}drich, S. and Seise, E. and Krebs, M. and Tavella, F. and Willner, A. and Duesterer, S. and Schlarb, H. and Feldhaus, J. and Limpert, J. and Rossbach, J. and T{\"{u}}nnermann, A. (Optics Express, 2010)
We report on a high power optical parametric amplifier delivering 8 fs pulses with 6 GW peak power. The system is pumped by a fiber amplifier and operated at 96 kHz repetition rate. The average output power is as high as 6.7 W, which is the highest average power few-cycle pulse laser reported so far. When stabilizing the seed oscillator, the system delivered carrier-envelop phase stable laser pulses. Furthermore, high harmonic generation up to the 33th order (21.8 nm) is demonstrated in a Krypton gas jet. In addition, the scalability of the presented laser system is discussed.
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Isotope shift of the 1s2p P-3(0)-1s2s S-1(0) level splitting in heavy He-like ions: Implications for atomic parity-nonconservation studies - Ferro, F.; Artemyev, A.; St{\"{o}}hlker, T.; Surzhykov, A. (Physical Review A, 2010)
Heavy He-like ions are considered to be promising candidates for atomic parity-nonconservation (PNC) studies, thanks to their relatively simple atomic structure and the significant mixing between the almost degenerate (for the atomic numbers Z 64 and Z 91) opposite-parity levels 1s2s 1S0 and 1s2p 3P0. A number of experiments exploiting this level mixing have been proposed, and their implementation requires a precise knowledge of the 2 3P0–2 1S0 energy splitting for different nuclear charges and isotopes. In this paper we performed a theoretical analysis of the level splitting, employing the relativistic many-body perturbation theory and including QED corrections for all isotopes in the intervals 54⩽Z⩽71 and 86⩽Z⩽93. Possible candidates for future experimental PNC studies are discussed.
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Spectrally resolved and phase-sensitive far-field measurement for the coherent addition of laser pulses in a tiled grating compressor - Hornung, M.; B{\"{o}}defeld, R.; Kessler, A.; Hein, J.; Kaluza, M.C. (Optics Letters, 2010)
We describe a method that can be used for the coherent addition of laser pulses. As different laser pulses are initially generated in a laser-pulse compressor equipped with a tiled grating, such a coherent addition is indispens able in order to maximize the intensity in the laser far field. We present measurements in this context where, up to now, an unavoidable difference in the grating constants between the phased gratings reduced the maximum achievable intensity. The method significantly facilitates the high-precision alignment of a tiled grating compressor and could also be used for a coherent addition of laser pulses.
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MATS and LaSpec: High-precision experiments using ion traps and lasers at FAIR - Rodr{\'{i}}guez, D.; Blaum, K.; N{\"{o}}rtersh{\"{a}user, W. and Ahammed, M. and Algora, A. and Audi, G. and {\"{A}}yst{\"{o}}, J. and Beck, D. and Bender, M. and Billowes, J. and Block, M. and B{\"{o}}hm, C. and Bollen, G. and Brodeur, M. and Brunner, T. and Bushaw, B. and Cakirli, R. and Campbell, P. and Cano-Ott, D. and Cort{\'{e}}s, G. and Crespo L{\'{o}}pez-Urrutia, J. and Das, P. and Dax, A. and De, A. and Delheij, P. and Dickel, T. and Dilling, J. and Eberhardt, K. and Eliseev, S. and Ettenauer, S. and Flanagan, K. and Ferrer, R. and Garc{\'{i}}a-Ramos, J.-E. and Gartzke, E. and Geissel, H. and George, S. and Geppert, C. and G{\'{o}}mez-Hornillos, M. and Gusev, Y. and Habs, D. and Heenen, P.-H. and Heinz, S. and Herfurth, F. and Herlert, A. and Hobein, M. and Huber, G. and Huyse, M. and Jesch, C. and Jokinen, A. and Kester, O. and Ketelaer, J. and Kolhinen, V. and Koudriavtsev, I. and Kowalska, M. and Kr{\"{a}mer, J. and Kreim, S. and Krieger, A. and K{\"{u}}hl, T. and Lallena, A. and Lapierre, A. and Le Blanc, F. and Litvinov, Y. and Lunney, D. and Mart{\'{i}}nez, T. and Marx, G. and Matos, M. and Minaya-Ramirez, E. and Moore, I. and Nagy, S. and Naimi, S. and Neidherr, D. and Nesterenko, D. and Neyens, G. and Novikov, Y. and Petrick, M. and Pla{\"{s}}, W. and Popov, A. and Quint, W. and Ray, A. and Reinhard, P.-G. and Repp, J. and Roux, C. and Rubio, B. and Sanchez, R. and Schabinger, B. and Scheidenberger, C. and Schneider, D. and Schuch, R. and Schwarz, S. and Schweikhard, L. and Seliverstov, M. and Solders, A. and Suhonen, M. and Szerypo, J. and Ta{\'{i}}n, J. and Thirolf, P. and Ullrich, J. and Duppen, P. and Vasiliev, A. and Vorobjev, G. and Weber, C. and Wendt, K. and Winkler, M. and Yordanov, D. and Ziegler, F. (The European Physical Journal Special Topics, 2010)
Nuclear ground state properties including mass, charge radii, spins and moments can be determined by applying atomic physics techniques such as Penning-trap based mass spectrometry and laser spectroscopy. The MATS and LaSpec setups at the low-energy beamline at FAIR will allow us to extend the knowledge of these properties further into the region far from stability. The mass and its inherent connection with the nuclear binding energy is a fundamental property of a nuclide, a unique “fingerprint”. Thus, precise mass values are important for a variety of applications, ranging from nuclear-structure studies like the investigation of shell closures and the onset of deformation, tests of nuclear mass models and mass formulas, to tests of the weak interaction and of the Standard Model. The required relative accuracy ranges from 10^−5 to below 10^−8 for radionuclides, which most often have half-lives well below 1 s. Substantial progress in Penning trap mass spectrometry has made this method a prime choice for precision measurements on rare isotopes. The technique has the potential to provide high accuracy and sensitivity even for very short-lived nuclides. Furthermore, ion traps can be used for precision decay studies and offer advantages over existing methods. With MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly-charged ions) at FAIR we aim to apply several techniques to very short-lived radionuclides: High-accuracy mass measurements, in-trap conversion electron and alpha spectroscopy, and trap-assisted spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high-precision Penning trap system for mass measurements and decay studies. For the mass measurements, MATS offers both a high accuracy and a high sensitivity. A relative mass uncertainty of 10^−9 can be reached by employing highly-charged ions and a non-destructive Fourier-Transform Ion-Cyclotron-Resonance (FT-ICR) detection technique on single stored ions. This accuracy limit is important for fundamental interaction tests, but also allows for the study of the fine structure of the nuclear mass surface with unprecedented accuracy, whenever required. The use of the FT-ICR technique provides true single ion sensitivity. This is essential to access isotopes that are produced with minimum rates which are very often the most interesting ones. Instead of pushing for highest accuracy, the high charge state of the ions can also be used to reduce the storage time of the ions, hence making measurements on even shorter-lived isotopes possible. Decay studies in ion traps will become possible with MATS. Novel spectroscopic tools for in-trap high-resolution conversion-electron and charged-particle spectroscopy from carrier-free sources will be developed, aiming e.g. at the measurements of quadrupole moments and E0 strengths. With the possibility of both high-accuracy mass measurements of the shortest-lived isotopes and decay studies, the high sensitivity and accuracy potential of MATS is ideally suited for the study of very exotic nuclides that will only be produced at the FAIR facility.Laser spectroscopy of radioactive isotopes and isomers is an efficient and model-independent approach for the determination of nuclear ground and isomeric state properties. Hyperfine structures and isotope shifts in electronic transitions exhibit readily accessible information on the nuclear spin, magnetic dipole and electric quadrupole moments as well as root-mean-square charge radii. The dependencies of the hyperfine splitting and isotope shift on the nuclear moments and mean square nuclear charge radii are well known and the theoretical framework for the extraction of nuclear parameters is well established. These extracted parameters provide fundamental information on the structure of nuclei at the limits of stability. Vital information on both bulk and valence nuclear properties are derived and an exceptional sensitivity to changes in nuclear deformation is achieved. Laser spectroscopy provides the only mechanism for such studies in exotic systems and uniquely facilitates these studies in a model-independent manner.The accuracy of laser-spectroscopic-determined nuclear properties is very high. Requirements concerning production rates are moderate; collinear spectroscopy has been performed with production rates as few as 100 ions per second and laser-desorption resonance ionization mass spectroscopy (combined with β-delayed neutron detection) has been achieved with rates of only a few atoms per second.This Technical Design Report describes a new Penning trap mass spectrometry setup as well as a number of complementary experimental devices for laser spectroscopy, which will provide a complete system with respect to the physics and isotopes that can be studied. Since MATS and LaSpec require high-quality low-energy beams, the two collaborations have a common beamline to stop the radioactive beam of in-flight produced isotopes and prepare them in a suitable way for transfer to the MATS and LaSpec setups, respectively.
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Parity-nonconservation effect with the laser-induced 2 3S1 - 2 1S0 transition in heavy heliumlike ions - Shabaev, V. M.; Volotka, A. V.; Kozhuharov, C.; Plunien, G.; St{\"{o}}hlker, T. (Physical Review A, 2010)
The parity-nonconservation (PNC) effect on the laser-induced 2 3S1–2 1S0 transition in heavy heliumlike ions is considered. A simple analytical formula for the PNC correction to the cross section is derived for the case, when the opposite-parity 2 1S0 and 2 3P0 states are almost degenerate and, therefore, the PNC effect is strongly enhanced. Numerical results are presented for heliumlike gadolinium and thorium, which seem the most promising candidates for such experiments. In both Gd and Th cases the photon energy required will be anticipated with a high-energy laser built at GSI. Alternatively, it can be gained with ultraviolet lasers utilizing relativistic Doppler tuning at FAIR facilities in Darmstadt.
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Geometry-Temperature Interplay in the Casimir Effect - Gies, H.; Weber, A. (International Journal of Modern Physics A, 2010)
We discuss Casimir phenomena which are dominated by long-range fluctuations. A prime example is given by Casimir phenomena where thermal fluctuations in open Casimir geometries can induce significantly enhanced thermal corrections. We illustrate the underlying mechanism with the aid of the inclined-plates configuration, giving rise to enhanced power-law temperature dependences compared to the parallel-plates case. In limiting cases, we find numerical evidence even for fractional power laws induced by long-range fluctuations. We demonstrate that thermal energy densities for open geometries are typically distributed over length scales of 1/T. As an important consequence, approximation methods for thermal corrections based on local energy-density estimates such as the proximity-force approximation are expected to become unreliable even at small surface separations.
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High‐Contrast Ultrafast OPA Module For The PHELIX Facility - Bagnoud, V.; Fils, J.; Hein, J.; Kaluza, M.C.; Paulus, G.G.; St{\"{o}}hlker, T.; Wolf, M. (AIP Conference Proceedings, 2010)
In this paper, a new system for improvement of the pulse contrast in CPA laser systems by use of an ultrafast OPA is reviewed together with a scheme to create sub‐picosecond synchronized OPA pump pulses. The scheme is being implemented at the PHELIX facility at GSI‐Darmstadt, Germany.
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Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases - Seres, J.; Seres, E.; Hochhaus, D.; Ecker, B.; Zimmer, D.; Bagnoud, V.; K{\"{u}}hl, T.; Spielmann, C. (Nature Physics, 2010)
We present a new method for parametric amplification of soft-X-ray radiation. The laser-driven amplifier is based on parametric stimulated emission and is seeded with high-order-harmonic radiation generated in the same medium. The exponential increase of the soft-X-ray yield with increasing atomic density is experimentally demonstrated for two different sets of laser parameters. A small-signal gain up to 8 × 10^3 is obtained in both experiments at about 40 eV in argon using 350-fs-long laser pulses and with 6-fs-long ones at about 260 eV in helium, respectively. This new scheme reduces the pumping threshold for lasing with a comparable conversion efficiency into the millijoule level, which is about two orders of magnitude smaller compared with the conventional plasma X-ray lasers. With a simple model, we can estimate the necessary experimental conditions for identifying the spectral range and the magnitude of the maximum gain, which are in reasonable agreement with our measurements.
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Multiterawatt peak power generated by the all diode pumped laser{–}POLARIS - Hein, J.; Hornung, M.; B{\"{o}}defeld, R.; Podleska, S.; S{\"{a}vert, A. and Wachs, R. and Kessler, A. and Keppler, S. and Wolf, M. and Polz, J. and J{\"{a}ckel, O. and Nicolai, M. and Schnepp, M. and K{\"{o}}rner, J. and Kaluza, M.C. and Paulus, G.G. (AIP Conference Proceedings, 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.
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Fiber-amplifier pumped high average power few-cycle pulse non-collinear OPCPA - Tavella, F.; Willner, A.; Rothhardt, J.; H{\"{a}drich, S. and Seise, E. and Duesterer, S. and Tschentscher, T. and Schlarb, H. and Feldhaus, J. and Limpert, J. and T{\"{u}}nnermann, A. and Rossbach, J. (Optics Express, 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.
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96^Ru(p,γ)97^Rh measurement at the GSI storage ring - Zhong, Q.; Aumann, T.; Bishop, S.; Blaum, K.; Boretzky, K.; Bosch, F.; Br{\"{a}uning, H. and Brandau, C. and Davinson, T. and Dillmann, I. and Ershova, O. and Geissel, H. and Gy{\"{u}}rky, G. and Heil, M. and K{\"{a}ppeler, F. and Keli{}, A. and Kozhuharov, C. and Langer, C. and Bleis, T. L. and Litvinov, Y. A. and Lotay, G. and Marganiec, J. and Petridis, N. and Plag, R. and Popp, U. and Reifarth, R. and Riese, B. and Rigollet, C. and Scheidenberger, C. and Simon, H. and St{\"{o}}hlker, T. and Sz{\"{u}}cs, T. and Weber, G. and Weick, H. and Winters, D. F. A. and Winters, N. and Woods, P. J. (Journal of Physics: Conference Series, 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.
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CW seeded optical parametric amplifier providing wavelength and pulse duration tunable nearly transform limited pulses - H{\"{a}drich, S. and Gottschall, T. and Rothhardt, J. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 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.
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Optimization of a tabletop high-repetition-rate soft x-ray laser pumped in double-pulse single-beam grazing incidence - Zimmer, D.; Zielbauer, B.; Pittman, M.; Guilbaud, O.; Habib, J.; Kazamias, S.; Ros, D.; Bagnoud, V.; K{\"{u}}hl, T. (Optics Letters, 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.
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Progress in the applicability of plasma X-ray lasers - K{\"{u}}hl, T.; Aurand, B.; Bagnoud, V.; Ecker, B.; Eisenbarth, U.; Guilbaud, O.; Fils, J.; Goette, S.; Habib, J.; Hochhaus, D.; Javorkova, D.; Neumayer, P.; et al. (Hyperfine Interactions, 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.
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Spectral Shape of the Two-Photon Decay of the 2 1S0 State in He-Like Tin - Trotsenko, S.; Kumar, A.; Volotka, A. V.; Bana{ś}, D.; Beyer, H. F.; Br{\"{a}uning, H. and Fritzsche, S. and Gumberidze, A. and Hagmann, S. and Hess, S. and Jagodzinski, P. and Kozhuharov, C. and Reuschl, R. and Salem, S. and Simon, A. and Spillmann, U. and Trassinelli, M. and Tribedi, L. C. and Weber, G. and Winters, D. and St{\"{o}}hlker, T. (Physical Review Letters, 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.
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Catalysis of Schwinger vacuum pair production - Dunne, G.; Gies, H.; Sch{\"{u}}tzhold, R. (Physical Review D, 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.
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Compact fiber amplifier pumped OPCPA system delivering Gigawatt peak power 35 fs pulses - Rothhardt, J.; H{\"{a}drich, S. and Gottschall, T. and Clausnitzer, T. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 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.
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Polarized tunable monoenergetic x-rays produced by radiative electron capture into the K-shell of Xe^(54+) - Hess, S.; Br{\"{a}uning, H. and Spillmann, U. and Geyer, S. and Hagmann, S. and Kozhuharov, C. and Krings, T. and Kumar, A. and M{\"{a}rtin, R. and O'Rourke, B. E. and Reuschl, R. and Trotsenko, S. and Weber, G. and Winters, D. and St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 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.
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Wavelength-independent all-optical synchronization of a Q-switched 100-ps microchip laser to a femtosecond laser reference source - Nodop, D.; Rothhardt, J.; H{\"{a}drich, S. and Limpert, J. and T{\"{u}}nnermann, A. (Applied Physics B, 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.
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Observation of the 2p_(3/2) → 2s_(1/2) intra-shell transition in He-like uranium - Trassinelli, M.; Kumar, A.; Beyer, H. F.; Indelicato, P.; M{\"{a}rtin, R. and Reuschl, R. and Kozhedub, Y. S. and Brandau, C. and Br{\"{a}uning, H. and Geyer, S. and Gumberidze, A. and Hess, S. and Jagodzinski, P. and Kozhuharov, C. and Liesen, D. and Spillmann, U. and Trotsenko, S. and Weber, G. and Winters, D. F. A. and St{\"{o}}hlker, T. (Europhysics Letters, 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.
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Beam lifetimes and ionization cross sections of U^(28+) - Weber, G.; Omet, C.; DuBois, R. D.; de Lucio, O.; St{\"{o}}hlker, T.; Brandau, C.; Gumberidze, A.; Hagmann, S.; Hess, S.; Kozhuharov, C.; Reuschl, R.; Spiller, P.; et al. (Physical Review Special Topics - Accelerators and Beams, 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.
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Generation of flattop pump pulses for OPCPA by coherent pulse stacking with fiber Bragg gratings - Rothhardt, J.; H{\"{a}drich, S. and Gottschall, T. and Limpert, J. and T{\"{u}}nnermann, A. and Rothhardt, M. and Becker, M. and Br{\"{u}}ckner, S. and Bartelt, H. (Optics Express, 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.
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Application of LTS-SQUIDs in Nuclear Measurement Techniques - Steppke, A.; Geithner, R.; Hechler, S.; Nawrodt, R.; Neubert, R.; Vodel, W.; Schwickert, M.; Reeg, H.; Seidel, P. (IEEE Transactions on Applied Superconductivity, 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.
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Polarization studies of radiative electron capture into highly-charged uranium ions - Hess, S.; Br{\"{a}uning, H. and Spillmann, U. and Brandau, C. and Geyer, S. and Hagmann, S. and Hegewald, M. and Kozhuharov, C. and Krings, T. and Kumar, A. and M{\"{a}rtin, R. and Proti{}, D. and O'Rourke, B. and Reuschl, R. and Trassinelli, M. and Trotsenko, S. and Weber, G. and Winters, D. F. A. and St{\"{o}}hlker, T. (Journal of Physics: Conference Series, 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.
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Polarization and angular correlation studies of X-rays emitted in relativistic ion-atom collisions - St{\"{o}}hlker, T.; Bana{ś}, D.; Br{\"{a}uning, H. and Fritzsche, S. and Geyer, S. and Gumberidze, A. and Hagmann, S. and Hess, S. and Kozhuharov, C. and Kumar, A. and M{\"{a}rtin, R. and O’Rourke, B. E. and Reuschl, R. and Spillmann, U. and Surzhykov, A. and Tashenov, S. and Trotsenko, S. and Weber, G. and Winters, D. F. A. (The European Physical Journal - Special Topics, 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.
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Polarization Measurements of Radiative Electron Capture Transitions in Highly Charged Ions - Br{\"{a}uning, H. and Hess, S. and Geyer, S. and Spillmann, U. and Kozhuharov, Ch. and Krings, Th. and Kumar, A. and M{\"{a}rtin, R. and Proti{}, D. and Reuschl, R. and Trassinelli, M. and Trotsenko, S. and Weber, G. and Winters, D. and St{\"{o}}hlker, T. (AIP Conference Proceedings, 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.
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Spectral shape of the 2E1 decay from 2s state in He-like tin - Kumar, A.; Trotsenko, S.; Volotka, A. V.; Bana{ś}, D.; Beyer, H. F.; Br{\"{a}uning, H. and Gumberidze, A. and Hagmann, S. and Hess, S. and Kozhuharov, C. and Reuschl, R. and Spillmann, U. and Trassinelli, M. and Weber, G. and St{\"{o}}hlker, T. (The European Physical Journal - Special Topics, 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.
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Ultra-wide parametric amplification at 800 nm toward octave spanning. - Aguergaray, C.; Schmidt, O.; Rothhardt, J.; Schimpf, D.; Descamps, D.; Petit, S.; Limpert, J.; Cormier, E. (Optics Express, 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.
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80 kHz repetition rate high power fiber amplifier flat-top pulse pumped OPCPA based on BIB₃O₆ - Rothhardt, J.; H{\"{a}drich, S. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 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.
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High energy ultrashort pulses via hollow fiber compression of a fiber chirped pulse amplification system - H{\"{a}drich, S. and Rothhardt, J. and Eidam, T. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 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.
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A 325-W-Average-Power Fiber CPA System Delivering Sub-400 fs Pulses - Eidam, T.; H{\"{a}drich, S. and R{\"{o}}ser, F. and Seise, E. and Gottschall, T. and Rothhardt, J. and Schreiber, T. and Limpert, J. and T{\"{u}}nnermann, A. (IEEE Journal of Selected Topics in Quantum Electronics, 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.
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High Repetition Rate Gigawatt Peak Power Fiber Laser Systems: Challenges, Design, and Experiment - Limpert, J.; Fabian, R.; Schimpf, D.; Seise, E.; Eidam, T.; H{\"{a}drich, S. and Rothhardt, J. and Jauregui, C. and T{\"{u}}nnermann, A. (IEEE Journal of Selected Topics in Quantum Electronics, 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.
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Degenerate optical parametric amplifier delivering sub 30 fs pulses with 2GW peak power - H{\"{a}drich, S. and Rothhardt, J. and R{\"{o}}ser, F. and Gottschall, T. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 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.
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500 MW peak power degenerated optical parametric amplifier delivering 52 fs pulses at 97 kHz repetition rate - Rothhardt, J.; H{\"{a}drich, S. and R{\"{o}}ser, F. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2008)
We present a high peak power degenerated parametric amplifier operating at 1030 nm and 97 kHz repetition rate. Pulses of a state-of-the art fiber chirped-pulse amplification (FCPA) system with 840 fs pulse duration and 410 µJ pulse energy are used as pump and seed source for a two stage optical parametric amplifier. Additional spectral broadening of the seed signal in a photonic crystal fiber creates enough bandwidth for ultrashort pulse generation. Subsequent amplification of the broadband seed signal in two 1 mm BBO crystals results in 41 µJ output pulse energy. Compression in a SF 11 prism compressor yields 37 µJ pulses as short as 52 fs. Thus, pulse shortening of more than one order of magnitude is achieved. Further scaling in terms of average power and pulse energy seems possible and will be discussed, since both concepts involved, the fiber laser and the parametric amplifier have the reputation to be immune against thermo-optical effects.
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Ionization of Heavy Ions in Collisions with Neutral Atoms at Relativistic Energies - Andreev, S. N.; Beigman, I. L.; Tolstikhina, I. Y.; Shevelko, V. P.; Baur, G.; St{\"{o}}hlker, T. (Bulletin of the Lebedev Physics Institute, 2008)
Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z approximate to 80-90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.
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Single-polarization ultra-large-mode-area Yb-doped photonic crystal fiber - Schmidt, O.; Rothhardt, J.; Eidam, T.; R{\"{o}}ser, F.; Limpert, J.; T{\"{u}}nnermann, A.; Hansen, K. P.; Jakobsen, C.; Broeng, J. (Optics Express, 2008)
We report on an ytterbium-doped single-transverse-mode rod-type photonic crystal fiber that combines the advantages of low nonlinearityand intrinsic polarization stability. The mode-field-area of the fundamental mode is as large as 2300 µm2. An output power of up to 163 W with adegree of polarization better than 85% has been extracted from a simple fiber laser setup without any additional polarizing element within the cavity than the fiber itself. The beam quality has been characterized by a M2 value of 1.2. The single-polarization window ranges from 1030 to 1080 nm, hence possesses an excellent overlap with the gain profile of ytterbium-doped silica fibers. To the best of our knowledge this fiber design has the largest mode-field-diameter ever reported for polarizing or even polarization maintaining rare-earth-doped double-clad fibers.
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High repetition rate fiber amplifier pumped sub-20 fs optical parametric amplifier - Rothhardt, J.; H{\"{a}drich, S. and Schimpf, D. and Limpert, J. and T{\"{u}}nnermann, A. (Optics Express, 2007)
We report on a high repetition rate noncollinear optical parametric amplifier system (NOPA) based on a cavity dumped Ti:Sapphire oscillator providing the signal, and an Ytterbium-doped fiber amplifier pumping the device. Temporally synchronized NOPA pump pulses are created via soliton generation in a highly nonlinear photonic crystal fiber. This soliton is fiber amplified to high pulse-energies at high repetition rates. The broadband Ti:Sapphire laser pulses are parametrically amplified either directly or after additional spectral broadening. The approach of fiber-based pump-pulse generation from a femtosecond laser, that emits in the spectral region of NOPA-gain, offers enhanced long-term stability and pulse quality compared to conventional techniques, such as signal pulse generation from a high power laser system via filamentation in bulk media. The presented system produces high-energy ultra-short pulses with pulse-durations down to 15.6 fs and pulse-energies up to 500 nJ at a repetition rate as high as 2 MHz.
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Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system - R{\"{o}}ser, F.; Eidam, T.; Rothhardt, J.; Schmidt, O.; Schimpf, D.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2007)
We report on an ytterbium-doped fiber chirped-pulse amplification (CPA) system delivering millijoule level pulse energy at repetition rates above 100 kHz corresponding to an average power of more than 100 W. The compressed pulses are as short as 800 fs. As the main amplifier, an 80 µm core diameter short length photonic crystal fiber is employed, which allows the generation of pulse energies up to 1.45 mJ with a B-integral as low as 7 at a stretched pulse duration of 2 ns. A stretcher-compressor unit consisting of dielectric diffraction gratings is capable of handling the average power without beam and pulse quality distortions. To our knowledge, we present the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems.
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Theoretical analysis of the gain bandwidth for noncollinear parametric amplification of ultrafast pulses - Schimpf, D. N.; Rothhardt, J.; Limpert, J.; T{\"{u}}nnermann, A.; Hanna, D. C. (Journal of the Optical Society of America B, 2007)
The choice of optimum phase-matching conditions for noncollinear optical parametric amplifiers is usually made on the basis of the linear spectral dispersion characteristics of the anisotropic nonlinear crystal. However, for high-peak-power operation, where pump depletion is involved, it is shown that the tolerance of the parametric gain with regard to k-vector mismatch is to change the optimum phase-matching parameters. Our calculations show that, with the revised parameters, an enhancement in peak power approaching 50% could be achieved.
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Beam lifetimes for low-charge-state heavy ions in the GSI storage rings - DuBois, R.; Lucio, O. d.; Thomason, M.; Weber, G.; St{\"{o}}hlker, T.; Beckert, K.; Beller, P.; Bosch, F.; Brandau, C.; Gumberidze, A.; Hagmann, S.; Kozhuharov, C.; et al. (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007)
Lifetimes for 10 – 50 MeV/u U28+ ions were measured for base vacuum conditions in the ESR storage ring at GSI-Darmstadt. The lifetimes are due to total electron loss from U28+ resulting from interactions with background gases in the ring. Lifetimes were also measured for interactions with H2 and N2 targets. These data provide information about the relative magnitudes and energy dependences of the stripping cross-sections resulting from interactions with H2 and N2, gases which represent the primary constituents in high and ultra-high vacuum environments.
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Millijoule pulse energy Q-switched short-length fiber laser - Schmidt, O.; Rothhardt, J.; R{\"{o}}ser, F.; Linke, S.; Schreiber, T.; Rademaker, K.; Limpert, J.; Ermeneux, S.; Yvernault, P.; Salin, F.; T{\"{u}}nnermann, A. (Optics Letters, 2007)
We report on a Q-switched short-length fiber laser producing 100 W of average output power at 100 kHz repetition rate and pulse durations as short as 17 ns. Up to 2 mJ of energy and sub-10-ns pulse duration are extracted at lower repetition rates. This performance is obtained by employing a rod-type ytterbium-doped photonic crystal fiber with a 70 microm core as gain medium, allowing for very short pulse durations, high energy storage, and emission of a single-transverse-mode beam.
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Parametric amplification and compression to ultrashort pulse duration of resonant linear waves - Aguergaray, C.; Andersen, T.; Schimpf, D.; Schmidt, O.; Rothhardt, J.; Schreiber, T.; Limpert, J.; Cormier, E.; T{\"{u}}nnermann, A. (Optics Express, 2007)
We report on an optical parametric amplification system which is pumped and seeded by fiber generated laser radiation. Due to its low broadening threshold, high spatial beam quality and high stability, the fiber based broad bandwidth signal generation is a promising alternative to white light generation in bulky glass or sapphire plates. We demonstrate a novel and successful signal engineering implemented in a setup for parametric amplification and subsequent recompression of resonant linear waves resulting from soliton fission in a highly nonlinear photonic crystal fiber. The applied pump source is a high repetition rate ytterbium-doped fiber chirped pulse amplification system. The presented approach results in the generation of \ 50 fs pulses at MHz repetition rate. The potential of generating even shorter pulse duration and higher pulse energies will be discussed.
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Investigation of the Decay Properties of the 1s(2s) 2 State in Li-Like Uranium - Trotsenko, S.; St{\"{o}}hlker, T.; Bana{ś}, D.; Dong, C. Z.; Fritzsche, S.; Gumberidze, A.; Hagmann, S.; Hess, S.; Indelicato, P.; Kozhuharov, C.; Nofal, M.; Reuschl, R.; et al. (Journal of Physics: Conference Series, 2007)
We report on an experiment aiming for a study of the radiative decay modes of the 1s (2s)2 level in Li-like uranium. The experiment was performed of initially Be-like uranium colliding with N2 molecules at an energy of 90 MeV/u. By measuring the x-ray production associated with K-shell ionization of the projectile, a high selectivity for the production of the 1s (2s)2 level is observed.
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Radiative processes studied for bare uranium ions in collisions with H_2 - Weber, G.; St{\"{o}}hlker, T.; Bana{ś}, D.; Fritzsche, S.; Gumberidze, A.; Hagmann, S.; Hess, S.; Kozhuharov, C.; Nofal, M.; Popp, U.; Reuschl, R.; Spillmann, U.; et al. (Journal of Physics: Conference Series, 2007)
Radiative processes occurring in collision of decelerated bare uranium ions and molecular hydrogen are studied at the heavy-ion storage ring ESR. The combination of the deceleration technique and the narrow Compton profile of molecular hydrogen allowed us to resolve a multitude of REC transitions into the bound states of the projectile and to resolve unambiguously the tip region of primary bremsstahlung. For this purpose, a supersonic molecular hydrogen jet-target, precooled with liquid nitrogen and optimized for long-term stability, was applied.
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Recent experimental developments for the Lamb shift investigation in heavy ions - Reuschl, R.; Bana{ś}, D.; Beyer, H. F.; Chatterjee, S.; Gumberidze, A.; Hess, S.; Krings, T.; Liesen, D.; Proti{}, D.; Spillmann, U.; St{\"{o}}hlker, T.; Trassinelli, M.; et al. (Journal of Physics: Conference Series, 2007)
The latest commissioning experiment of a two arm transmission crystal x-ray spectrometer along with high-performance position-sensitive microstrip germanium detectors is presented. The goal of the experiment was to observe with high resolution the Ly-α-transitions of H-like Pb 81+ produced in collisions with Kr atoms. Due to a photon efficiency of only 10^−8 the position sensitivity as well as the energy and time resolution of segmented solid state Germanium detectors are absolutely essential for experiments using crystal x-ray spectrometers dealing with beams of heavy ions. A detector system with the desired properties has become available through a collaboration with the Forschungszentrum J{\"{u}}lich.
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Extended single-mode photonic crystal fiber lasers - Limpert, J.; Schmidt, O.; Rothhardt, J.; R{\"{o}}ser, F.; Schreiber, T.; T{\"{u}}nnermann, A.; Ermeneux, S.; Yvernault, P.; Salin, F. (Optics Express, 2006)
We report on an ytterbium-doped photonic crystal fiber with a core diameter of 60 microm and mode-field-area of 2000 µm^2 of the emitted fundamental mode. Together with the short absorption length of 0.5 m this fiber possesses a record low nonlinearity which makes this fiber predestinated for the amplification of short laser pulses to very high peak powers. In a first continuous-wave experiment a power of 320 W has been extracted corresponding to 550 W per meter. To our knowledge this represents the highest power per unit length ever reported for fiber lasers. Furthermore, the robust single-transverse-mode propagation in a passive 100 microm core fiber with a similar design reveals the potential of extended large-mode-area photonic crystal fibers.
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131 W 220 fs fiber laser system - R{\"{o}}ser, F.; Rothhardt, J.; Ortac, B.; Liem, A.; Schmidt, O.; Schreiber, T.; Limpert, J.; T{\"{u}}nnermann, A. (Optics Letters, 2005)
We report on an ytterbium-doped photonic-crystal-fiber-based chirped-pulse amplification system delivering 131 W average power 220 fs pulses at 1040 nm center wavelength in a diffraction-limited beam. The pulse repetition rate is 73 MHz, corresponding to a pulse energy of 1.8 µJ and a peak power as high as 8.2 MW.
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Search for 1s2s S-3(1)-1s2p P-3(2) decay in U90+ - Beiersdorfer, P.; Elliott, S. R.; Osterheld, A.; St{\"{o}}hlker, T.; Autrey, J.; Brown, G. V.; Smith, A. J.; Widmann, K. (Physical Review A, 1996)
We present high-resolution crystal-spectrometer measurements that cover the wavelength range 3.0-3.2 Angstrom containing the electric-dipole-allowed 2s(1/2)-2p(3/2) transitions in highly charged uranium ions. Strong features from 2s(1/2)-2p(3/2) transitions in lithiumlike, berylliumlike, and boronlike uranium were observed. In addition, a weak feature with intensity just above the level of background fluctuations was observed at the predicted location of the 1s2s S-3(1)-1s2p P-3(2) transition in heliumlike U90+. The feature was observed in spectra where the intensity of the 2s(1/2)-2p(3/2) transition in lithiumlike uranium, and thus the ionization balance, was optimized; it appeared absent in spectra where the average ionization balance was lower. The measured energy of the feature is 4510.05+/-0.24 eV, which agrees closely with the values predicted for the 1s2s S-3(1)-1s2p P-3(2) transition by recent theories. Detailed spectral modeling calculations indicate the possibility that a weak transition in berylliumlike U88+ is situated within 4 eV of the-location of the heliumlike S-3(1)-P-3(2) transition. This transition connects the level 1s (2)2p(1/2)2p(3/2) (3)p(1) with the 1s (2)2s(1/2)2p(1/2) P-3(0) metastable ground level in berylliumlike uranium. The accuracy with which the energy of the berylliumlike transition can be predicted is insufficient to rule out a blend with the heliumlike S-3(1)-P-3(2) transition.
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The physics of highly charged heavy ions revealed by storage/cooler rings - Mokler, P. H.; St{\"{o}}hlker, T. (Advances in Atomic, Molecular, and Optical Physics, 1996)
This chapter presents an overview of the current advances in the rapidly developing field of heavy ion accelerator technology. Now, essential aspects in this area are accessible. In the meantime, great progress already has been made in the fundamental physics in this field. This is particularly true for achievements in the atomic physics of highly charged heavy ions. There are two general domains to be considered in the atomic physics of highly charged heavy ions: the fields of collisions and of atomic structure. Both aspects have to be explored equally because they are strongly interconnected. The interaction processes has to be investigated to know, for instance, the population of excited states to help answer questions on the atomic structure; conversely, the structure has to be known to understand the interactions. In both the fields, fundamental principles can be studied uniquely. This is in particular true for the heaviest ion species with only a few- or even zero-electrons left.
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Measurement of 2-Electron Contributions to the Ground-State Energy of Helium-Like Ions - Marrs, R. E.; Elliott, S. R.; St{\"{o}}hlker, T. (Physical Review A, 1995)
We report direct measurements of two-electron contributions to the ground-state energy of high-Z heliumlike ions. The difference in radiative-recombination x-ray energy (i.e., ionization potential of the recombined ion) was measured for bare and hydrogenlike target ions trapped in an electron-beam ion trap for six elements ranging from Z = 32 to Z = 83. The achieved uncertainties (as small as 1.6 eV) test the second-order many-body contributions to the energy and approach the size of the two-electron (screened) Lamb shift: We also report a measurement of the ground-state ionization potential of heliumlike bismuth relative to heliumlike xenon. All results are in agreement with available theories.
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The X-Ray-Spectrum of H-Like Uranium - Mokler, P. H.; St{\"{o}}hlker, T.; Dunford, R. W.; Gallus, A.; Kandler, T.; Menzel, G.; Prinz, H. T.; Rymuza, P.; Stachura, Z.; Swiat, P.; Warczak, A. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1995)
By decelerating highly-charged, very heavy ions to low energies in the storage and cooler ring, ESR, a new brilliant source for projectile x-rays has been obtained. In a first precision spectroscopy experiment up to 2*10^7 stored bare U92+ ions have been decelerated down to 49 MeV/u before detecting the characteristic projectile x-rays associated with one-electron capture at the ESR gas target. The Lyman, Balmer and Paschen series are distinctly observed for hydrogenic U91+ ions.
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Measurement of the Ground-State Lambshift of Hydrogenlike Uranium at the Electron Cooler of the ESR - Beyer, H. F.; Menzel, G.; Liesen, D.; Gallus, A.; Bosch, F.; Deslattes, R.; Indelicato, P.; St{\"{o}}hlker, T.; Klepper, O.; Moshammer, R.; Nolden, F.; Eickhoff, H.; et al. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1995)
X-rays are emitted with the radiative recombination of free electrons in an electron cooler of a heavy-ion storage ring. Due to a small width of the X-ray lines, an observation angle close to 0 degrees and an accurate determination of the ion velocity, the ground-state Lambshift of hydrogenlike uranium (470 +/- 16) eV could be measured to an accuracy of 3.4%. A re-evaluation of a measurement of the 1S(1/2) Lambshift in hydrogenlike gold gave a new value of (202.3 +/- 7.9) eV as compared to the former value of (212 +/- 15) eV. The results are in excellent agreement with QED calculations and are more precise than any other measurements previously reported for a high-Z, hydrogenlike ion.
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Photon Angular-Distribution of Radiative Electron-Capture into the M-Shell of He-Like Uranium Ions at 110-140 MeV/u - Kandler, T.; St{\"{o}}hlker, T.; Mokler, P. H.; Kozhuharov, C.; Geissel, H.; Scheidenberger, C.; Rymuza, P.; Stachura, Z.; Warczak, A.; Dunford, R. W.; Eichler, J.; Ichihara, A.; et al. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1995)
Measurements of the photon angular distribution of Radiative Electron Capture into the M shell have been performed with He-like uranium ions in the range 110-140 MeV/u. In addition, L REC was studied at a projectile energy of 140 MeV/u. In both cases, the experimental data show an asymmetry around 90° and agree well with a fully relativistic theory.
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Radiative Electron-Capture Studied in Relativistic Heavy-Ion Atom Collisions - St{\"{o}}hlker, T.; Kozhuharov, C.; Mokler, P. H.; Warczak, A.; Bosch, F.; Geissel, H.; Moshammer, R.; Scheidenberger, C.; Eichler, J.; Ichihara, A.; Shirai, T.; Stachura, Z.; et al. (Physical Review A, 1995)
The process of radiative electron capture (REC) in relativistic collisions of high-Z ions with low-Z gaseous and solid targets is studied experimentally and theoretically. The observed x-ray spectra are analyzed with respect to photon angular distributions as well as to total K-REC cross sections. The experimental results for angle-differential cross sections are well reproduced by exact relativistic calculations which yield significant deviations from standard sin^2(θ) distributions. Total cross sections for K-REC are shown to follow a simple scaling rule obtained from exact relativistic calculations as well as from a nonrelativistic dipole approximation. The agreement between these different theoretical approaches must be regarded as fortuitous, but it lends support to the use of the nonrelativistic approach for practical purposes.
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Deviation from 1st-Order Perturbation-Theory Observed at Intermediate Relativistic Velocities for the Ionization of Highly-Charged Heavy Projectiles - Rymuza, P.; St{\"{o}}hlker, T.; Cocke, C. L.; Geissel, H.; Kozhuharov, C.; Mokler, H.; Moshammer, R.; Nickel, F.; Scheidenberger, C.; Stachura, Z.; Ullrich, J.; Warczak, A. (Journal of Physics B: Atomic, Molecular and Optical Physics, 1993)
Projectile K-shell ionization cross sections were measured for 80-200 MeV/u H- and He-like Bi ions incident on thin C, Al and Ni targets. The results are compared with predictions of first-order perturbation theories, RSCA and PWBA, as well as with experimental results published for Xe and U ions at similar ratios eta of projectile velocity to K-shell electron velocity. All experimental data lie a factor of 1.5 above theory for 0.6 < eta < 1.5.
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Single and Double Electron-Capture in Collisions of Highly Ionized, Decelerated Ge Ions with Ne - St{\"{o}}hlker, T.; Kozhuharov, C.; Mokler, P. H.; Olson, R. E.; Stachura, Z.; Warczak, A. (Journal of Physics B: Atomic, Molecular and Optical Physics, 1992)
Experimental cross sections for non-radiative single and double electron capture from Ne target into decelerated H-like Ge ions at collision energies of (4-12) MeV u-1 are presented. The results are compared with theoretical calculations and an empirical scaling rule. Information concerning the impact parameter dependence of electron capture is extracted using classical trajectory Monte Carlo calculations.
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Ground-State Transitions in One-Electron and 2-Electron Bi Projectiles - St{\"{o}}hlker, T.; Mokler, P. H.; Geissel, H.; Moshammer, R.; Rymuza, P.; Bernstein, E. M.; Cocke, C. L.; Kozhuharov, C.; M{\"{u}}nzenberg, G.; Nickel, F.; Scheidenberger, C.; Stachura, Z.; et al. (Physics Letters A, 1992)
By using segmented solid state X-ray detectors and applying X-ray/ charge-state selective particle coincidences, the ionic structures of Bi-83(82+) and Bi-83(81+) have been studied separately at 82 MeV/u under single collision conditions. The high granularity of the Ge(i) X-my detectors used allowed a partial Doppler correction for the X-ray events while maintaining a large total solid angle. An absolute precision of K-transition energies of 10(-3) is feasible; the relative accuracy is better than 30 eV. The experimental values compare very well with the theoretical transition energies in H- and He-like Bi ions.
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Radiative Electron-Capture into the K-Shell, L-Shell and M-Shell of Decelerated, Hydrogenic Ge Projectiles - St{\"{o}}hlker, T.; Kozhuharov, C.; Livingston, A. E.; Mokler, P. H.; Stachura, Z.; Warczak, A. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1992)
Radiative Electron Capture (REC) in 4 to 12 MeV/u Ge^31+ {–}> H2 collisions has been studied using an X-ray/particle coincidence technique. This technique allowed a systematic investigation of K-shell REC as well as a separation of REC into the projectile L- and M-shells. The cross sections are discussed within a general scaling picture based on the reduced projectile velocity.
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Equilibrium Charge State Distributions for Relativistic Heavy-Ions - St{\"{o}}hlker, T.; Geissel, H.; Folger, H.; Kozhuharov, C.; Mokler, P. H.; M{\"{u}}nzenberg, G.; Schardt, D.; Schwab, T.; Steiner, M.; Stelzer, H.; S{\"{u}}mmerer, K. (Nuclear Instruments { &} Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 1991)
Equilibrium charge-state distributions have been measured for 617.2 MeV/u Au and 758.2 MeV/u Xe projectiles traversing C, Al, and Pb targets. In all cases bare ions dominate the charge-state distributions as expected for such relativistic velocities. For both projectiles used, the Al target produced the largest fraction of bare ions. This result is in agreement with calculations and with measurements for uranium ions given in the literature. These first atomic physics measurements at the new SIS accelerator have been performed during commissioning of the fragment separator (FRS).
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Radiative Electron-Capture - a Tool for Structure Studies of Heavy Few-Electron Ions - Mokler, P. H.; St{\"{o}}hlker, T.; Kozhuharov, C.; Stachura, Z.; Warczak, A. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1991)
Radiative Electron Capture (REC) in collisions of hydrogenic germanium ions with hydrogen is measured for projectile energies between 4 and 12 MeV/u. Extrapolating the resulting centroid energies of the K-REC radiation to zero collision velocity the K-binding energy in helium-like germanium-ions is determined. The value compares well with the theoretical prediction. REC in atomic collisions is advertised as a spectroscopic tool for structure investigations of very heavy few-electron projectiles.
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Capture of Quasi-Free Electrons into Highly Charged, Heavy Projectiles - St{\"{o}}hlker, T.; Mokler, P. H.; Kozhuharov, C.; Livingston, E. A.; Ullrich, J. (Nuclear Instruments { &} Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 1991)
In collisions between highly charged, heavy ions and light target atoms at adiabaticity parameters of 0.5 less-than-or-equal-to v2/u2 less-than-or-equal-to 0.75, resonant transfer and excitation (RTE) is an important charge-exchange process. Experiments for medium Z-ions are reviewed. Special emphasis is given to the competing radiative electron capture (REC) process. The general dependences of REC are discussed. In particular, we elucidate results obtained by the triple X-ray/X-ray/charge-changed particle coincidence technique for hydrogenic projectiles up to 36Kr35+ ions. With this method we could isolate a single RTE resonance, the 2s2p1P1 state, which stabilizes radiatively to the metastable 1s2s1S0 state. This state can only decay via two photon emission (2E1). Applying the triple coincidence technique we observed additional strong photon coincidences induced by cascades following REC into high projectile states.
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2-Photon Decay of the 1s2s S-1(0) State in Kr-36(34+) Produced by Resonant Transfer and Excitation - St{\"{o}}hlker, T.; Kozhuharov, C.; Livingston, A. E.; Mokler, P. H.; Ullrich, J.; Fricke, B. (Zeitschrift F{\"{u}}r Physik D - Atoms Molecules and Clusters, 1991)
The doubly excited 2s2p 1P1 level of Kr34+ populated via resonant transfer and excitation (RTE) feeds selectively the metastable 1s2s 1S0 state which can only decay via simultaneous emission of two photons to the ground state 1s2 1S0. X-ray/X-ray coincidence measurements in heavy ion-atom collisions enable the direct measurement of the spectral distribution of the two-photon decay in He-like ions. In addition, we observe strong photon cascades induced by radiative electron capture.
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Evidence for Resonant 2-Electron Capture and Excitation in Collisions of H-Like Ge with Ne - Warczak, A.; Stachura, Z.; Szymanski, A.; St{\"{o}}hlker, T.; Kozhuharov, C.; Livingston, A. E.; Mokler, P. H.; Reusch, S. (Physics Letters A, 1990)
Evidence for resonant two-electron capture and excitation, i.e. the time-recersed double Auger process with radiative stabilitization, was found by measuring coincidences between two K-X-rays of a heavy ion associated with its double charge exchange. Hydrogen-like Ge31+ ions with energies of 4.5-11.5 MeV/u were directed into a neon gas target. Contributions from the double non-resonant transfer and excitation process are also discussed.
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Heavy-Ion Beam Tailoring Using Dielectronic Recombination - Mokler, P. H.; Reusch, S.; St{\"{o}}hlker, T. (Nuclear Instruments { &} Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 1989)
For non-naked highly-charged heavy ions, dielectronic recombination (DR) can be the dominant electron capture process. Depending on the kind of a DR resonance involved, cross sections may reach values up to 10^2-18 cm^2 at the peak maximum. The widths of the DR resonances are typically <1 eV. Tuning a merged electron beam with an internal temperature typically - 0.1 eV to the DR resonance, a well defined narrow part can be cut out of the original primary ion beam by this charge-exchange process. The charge-changed new beam is pretty (DE/E=10^-5). Acase study for Ge^31+ +e=Ge^30+** (2P^2^1D_2) is given. Technical applications of DR beam tailoring techniques at heavy-ion storage rings will be discussed.
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Resonant Transfer and Excitation in Swift, Heavy Few-Electron Projectiles - Mokler, P. H.; Reusch, S.; St{\"{o}}hlker, T.; Schuch, R.; Schulz, M.; Wintermeyer, G.; Stachura, Z.; Warczak, A.; M{\"{u}}ller, A.; Awaya, Y.; Kambara, T. (Radiation Effects and Defects in Solids, 1989)
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