Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors

We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between $0.1$ and $1.0 \ bar with different noble gases. Shocks propagated at {80 \pm 10 \ km/s} and experienced strong radiative cooling resulting in post-shock compressions of { \times 25 \pm 2}. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases (\sim$$4$ times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data.Comment: HEDLA 2016 conference proceeding

Statistical investigations of the beam stability of the double-pass amplified zinc soft X-ray laser at 21.2 nm

At the Prague asterix laser system (PALS) of the Academy of Sciences of the Czech Republic the 1-TW asterix iodine laser is used as a pump source for soft X-ray laser experiments. The prepulse technique was applied which is known to enhance the X-ray laser output at the J=0–1 transition dramatically. Since Zn slab targets were used the laser wavelength was 21.2 nm. A prepulse beam having 1.6 J was preceding the main pulse by 10 ns. The main and the prepulse beam are focused by two different optical systems separately. Implementing a half-cavity set-up for double-pass amplification using a Mo/Si multilayer mirror the X-ray laser output was 10 times stronger than at single pass amplification in a 3-cm long plasma. Double-pass amplification was observed to be most efficient when the pump pulse duration was at least 120 ps longer than the round trip time in the half-cavity. Under this fundamental condition the X-ray laser reached saturation in the double-pass regime containing 4 mJ energy what is proved to be enough for applications. In this contribution the X-ray laser features like divergence in two dimensions, the beam quality (symmetry), the pointing angle and the time-integrated output energy are investigated over more than 100 shots. To characterize the stability of the X-ray laser the shot distribution, the mean value and the standard deviation for these parameters are evaluated. For 18 shots in a series — achieved during one single day — the corresponding values are given and detailed chi-squared tests characterize the Zn X-ray laser as a robust tool suitable for applications. At PALS soft X-ray laser beam time can be reserved for external research groups

Study of the stability of beam characteristics of the neon-like Zn X-ray laser using a half cavity

At the Prague Asterix Laser System Center (PALS) the Asterix iodine laser delivering up to 700 J/0.5 ns is used as a pump source for X-ray laser experiments and applications. The prepulse technique was applied which is known to improve the neon-like X-ray laser output at the $J = 0 {-} 1$ transition dramatically. Since Zn slab targets were used the operating wavelength was 21.2 nm. A prepulse having up to 20 J precedes the main pulse by 10 ns. The main beam and the prepulse beam are focussed by two different optical systems separately and their foci are superimposed at the target surface. By implementing a half-cavity set-up for double-pass amplification using a Mo/Si multilayer mirror – which can be used for more than 100 shots – the X-ray laser output was more than 10 times stronger than at the single pass in a 30 mm long plasma. Double-pass amplification was observed to be most efficient when the pump pulse duration was at least 150 ps longer than the round trip time ($\approx 260$ ps) in the half-cavity. Under this fundamental condition the X-ray laser reached saturation in the double-pass regime containing approx. 4 mJ energy which has been proved to be enough for future applications. In this contribution, the X-ray laser features like divergence in two dimensions, the beam quality (symmetry), the pointing angle and the integrated intensity giving an estimation of the output energy are investigated over 110 shots. To characterize the stability of the X-ray laser the shot distribution, the mean value and the standard deviation for these parameters are evaluated. For 18 shots in a series – what was achievable during one day – the corresponding values are given, and a statistical analysis carrying out a chi-squared test characterize the Zn X-ray laser as a robust tool suitable for applications. In the future it is planned to allocate X-ray laser beam time to external research groups

Biological Action in and out of the Water Window

This study is dealing with the difference of radiation chemical yields of single and double strand breaks induced in plasmid DNA by photons inside and outside of the soft X-ray water window, i.e., in the wavelength range from 2.28 nm to 4.88 nm. Photons were generated by various plasma sources providing nanosecond and sub-nanosecond pulses of extreme ultraviolet, soft X-ray and X-ray radiation. DNA strand breaks were determined by agarose gel electrophoresis. Higher radiation chemical yields of both single and double strand breaks were found using picosecond and nanosecond sources of extreme ultraviolet and X-ray radiation

Microscopie interférentielle X-UV : un outil pour l'étude des endommagements des surfaces optiques

Nous présentons des résultats récents concernant des premières investigations de microscopie interférentielle par laser X-UV d'endommagement optique. Le laser X-UV utilisé est un laser collisionnel en régime quasi-stationnaire émettant à 21.2 nm, développé au Prague Asterix Laser System (PALS, Prague, République Tchèque). Des échantillons de silice fondue de haute qualité, avec ou sans rayure, étaient irradiées en face avant par un laser bleu, correspondant au 3^{\selectfont\fontsize{7}{9}{\textrm{\`{e}me}}} harmonique du laser à iode du PALS (1.315 $\mu$m), servant également à réaliser le laser X-UV à 21.2 nm. Celui-ci était utilisé, 5 ns après l'irradiation pour réaliser une imagerie microscopique et interférentielle de la face arrière de l'échantillon. Les résultats font apparaître des déformations locales transitoires. Des premières analyses mettent en évidence une probable variation de la rugosité de la surface. Cette démonstration expérimentale encourageante ouvre la voie à de futures investigations, notamment sur notre prochaine installation laser : LASERIX