J. Habib

Optimization of a tabletop high-repetition-rate soft x-ray laser pumped in double-pulse single-beam grazing incidence

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 microJ 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.

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.

Low energy prepulse for 10 Hz operation of a soft-x-ray laser

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

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.

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.

Recent progress on the LASERIX facility

The LASERIX facility provides coherent and short soft x-ray beams for scientific applications. The beams are generated through high intensity laser interaction with matter using two different schemes, plasma based soft x-ray lasers, and high order laser harmonic generation. We describe in this communication the present status of the facility. The LASERIX beamtime has been recently opened to external users. We present two typical experiments performed in that context with the facility. The first one is dedicated to the fundamental study of the plasma based soft x-ray laser, whereas the second uses the existing beam to study irradiation induced dammage in DNA samples. We present also the development performed on the soft x-ray laser source to improve its stability and high repetition rate operation.

Strand Breaks in DNA Samples Induced with LASERIX

Samples of plasmid DNA were irradiated with pulsed 18.9 nm radiation originating from a Mo X-ray laser pumped in GRIP configuration at the LASERIX facility [1]. Surface doses of up to 500 kGray were delivered with a repetition rate of 10 Hz and average pulse energy of 200 nJ. The occurrence of single and double strand breaks not present in controls having undergone the same treatment except for the XRL irradiation can be seen as a clear effect of the XRL irradiation. This confirms the role of direct effects in DNA damages as previously seen with low energy ions [2, 3] and electrons.

Double-pulse single-beam grazing-incidence pumping

The paper reports on the optimization of a table-top nickel-like molybdenum transient collisionally excited soft x-ray laser (SXRL) at 18.9 nm, performed by double-pulse single beam grazing incidence pumping (DGRIP) [1]. This scheme allows for the first time the full control of the pump laser parameters including the pre-pulse duration, optimally generating the SXRL amplifier under grazing incidence. The single beam geometry of collinear double-pulse propagation guarantees the ideal overlap of the pre- and main pulse from shot to shot, resulting in a more efficient, 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 10 Hz repetition rate without re-alignment under once optimized double pumping pulse parameters including energy ratio, time delay, pre- and main pulse duration and line focus width [1].

LASERIX : an open facility for developments of EUV and soft X-ray lasers and applications.

LASERIX is a high-power laser facility delivering High-repetition-rate XUV laser beams pumped by Titanium:Sapphire laser. The aim of this laser facility is to offer to the users community Soft XRLs in the 30-7 nm range and auxiliary IR beam for a broad range of applications. 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.