Boris Ecker

An improved double-pulse non-normal incidence pumping geometry for transient collisionally excited soft X-ray lasers

An optimized pumping geometry for transient collisionally excited soft X-ray lasers is presented, similar to the geometry proposed by [1]. In contrast to usual approaches, where a nanosecond pre-pulse is assumed to provide the optimal plasma preparation and a picosecond pulse performs the final heating- and excitation process, two pulses of equal duration in the range around 10 picoseconds are applied. Both pulses are produced in the front end of the CPA pump laser. They are focused onto the target with the same spherical mirror under non-normal incidence geometry, optimized for efficient traveling wave excitation for the main-pulse. A first experiment was performed on Ni-like palladium (14.7 nm) at less than 500mJ total pulse energy on the target. This proves that this configuration is at least as favorable as the standard GRIP scheme, providing much simpler and more reliable operation.

X-RAY LASER DEVELOPMENTS AT PHELIX

Development of x-ray lasers using the PHELIX laser at the GSI Helmholtz center for heavy-ion research [1] is targeting a number of applications of novel x-ray sources in combination with energetic heavy-ion beams. This includes Thomson scattering diagnostics of heavy-ion driven plasmas, x-ray opacity measurements, and x-ray laser spectroscopy of highly-charged ions. Developments centered on the application of a novel double-pulse GRIP-like pumping scheme, DGRIP, where nonnormal incidence geometry is used for both the pre- and the main pulse for transient pumped Ni-like x-ray lasers [2,3]. This scheme was used at lower energy levels to pump soft x-ray lasers in the 50 – 100 eV regime as well as for pulse energies above 100 J for the pumping of shorter wavelength soft x-ray lasers [4].

Characterization of a 10Hz double-pulse non-normal incidence pumped transient collisional Ni-like molybdenum soft x-ray laser for applications

Stable and reliable operation of a nickel-like molybdenum transient collisional soft x-ray laser at 18.9 nm demonstrated and studied with a 10Hz Ti:sapphire laser system proves the suitability of the double-pulse non-normal incidence pumping geometry for table-top high repetition soft x-ray lasers and broadens the attractiveness of x-ray lasers as sources of coherent radiation for various applications. X-ray laser emission with pulse energies well above 1 μJ is obtained for several hours at 10Hz repetition-rate without re-alignment under optimized double pumping pulse parameters including energy ratio, time delay, pulse duration and line focus width.

Versatile High-Energy and Short-Pulse Operation of PHELIX

PHELIX (Petawatt High Energy Laser for Heavy Ion Experiments) is a hybrid Ti:Sapphire / Nd:Glass laser system using large aperture amplifiers from the former Nova and Phebus laser systems at Livermore and Limeil, respectively, designed to offer pulse energies in access of 2 kJ and output power in the petawatt range. It is aiming mainly on combined experiments in plasma physics [2] and atomic physics [3] together with the GSI accelerator facility, and in preparation for the new FAIR facility for antiproton and ion research. Both nanosecond and sub-picosecond pulses can be supplied. Presently pulse energies up to 500 J are used, at pulse durations between 2 and 25 ns. Compressed pulses down to 500 fs are achieved after full amplification. The maximum output energy after the pulse compressor is limited by the damage threshold of the final grating. For 20 to 50 ps pulses, the maximal throughput energy is 300 J. For the pulses around 500-fs duration, it is reduced to 230 J. A special arrangement allows for the preparation of pulse pairs, where the duration of the pulses can be individually controlled between 2 and 200 ps. Recent experiments included the preparation of a plasma target for the interaction with energetic heavy ions [3], and the pumping of a plasma x-ray laser [4].

Demonstration of an efficient pumping scheme for a 7.36-nm Ni-like samarium soft x-ray laser

The demonstration of a 7.36 nm Ni-like Sm soft x-ray laser pumped by 36 J of a Nd:glass chirped pulse amplification laser is presented. Double-pulse single-beam non-normal incidence pumping was applied for the efficient soft x-ray laser generation. Here the applied technique included a new 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.

A technique for measuring B-integral in chirped-pulse amplifiers

We demonstrate a simple method for measuring the B-integral of CPA systems based on temporal diffraction. Two identical pulses sent into the amplifier under study create time replicas used to retrieve the B-integral accumulation.

Heavy-Ion Spectroscopy with X-Ray Lasers at GSI

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

High-brilliance double-stage soft x-ray laser pumped by multiple pulses applied in grazing incidence

A new compact scheme for a double-stage seeded x-ray laser is demonstrated. This laser is offering greatly improved beam quality and brilliance making it a useful tool for applications.

Towards high photon-number soft x-ray lasers

We present an experimental design to independently pump two soft X-ray laser media suitable for a seed-amplifier configuration. Both the seed and the amplifier target are operated in the TCE scheme utilizing the DGRIP technique with its intrinsic travelling wave excitation. Controlled injection of the seed X-ray laser into the amplifier medium is realized via a spherical XUV mirror. The experimental design is perfectly appropriate for benchmarking combined simulations of the ARWEN and DeepOne code. A first experiment at the PHELIX laser utilizing this scheme has been conducted, demonstrating signs of amplification and allowing for the direct measurement of the gain life time of a Ni-like silver SXRL.

Strong field amplification of XUV: phase matching aspects

The dependence of the yield of high-order harmonic generation (HHG) on several important experimental parameters has been successfully modeled in the last 20 years by taking into account the single atom response and propagation effects. We extended this description by adding a stimulated emission process and named it x-ray parametric amplification (XPA). Beyond the super-quadratic increase of the XUV signal, which can be explained only in a limited pressure range by HHG theory, other observed characteristics like exponential growth, gain narrowing, strong blue-shift, beam divergence, etc. and their dependence on laser intensity and gas pressure can be explained accurately only by the new XPA model. We experimentally demonstrated XPA in Argon in the spectral range of 40-50 eV in excellent agreement with the theory. XPA holds the promise to realize a new class of bright x-ray sources for spectroscopy.