Professor Justin Wark

Abstract:

Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented. (C) 1999 American Institute of Physics. [S0034-6748(99)62601-6].

Abstract:

Experimental measurements of the optimum pulse delay and pulse irradiance ratio for lasing at 7.3 nm in Ni-like samarium are shown to be explained by a simple model. Experimental x-ray laser outputs are also shown to be well fitted with a simple one-dimensional ASE variation of the laser output with increasing target length through saturation. The ASE model is modified to take account of the two lasing lines present in Ni-like lasing and compared to experimental laser output measurements for Ni-like Dy lasing at 5.86 nm and 6.37 nm. The good agreement of experimental data with the ASE model indicates that refraction, non-uniformity of the laser medium and other problems traditionally associated with x-ray lasing are not significant with double pulse pumping.

Abstract:

We report here the experiments of the saturated Ni-like x-ray lasers at 14 -6 nm from a refraction compensating double target driven at 20 TW.cm(-2) by a pair of 75 ps Nd-glass laser pulses separated by 2.2 ns. The output source size as well as the time history, divergence, energy and spatial profile of the output beams of the Ni-like x-ray lasers have been fully characterised. The narrow divergence (similar to 1 mrad), short pulse duration (similar to 40 ps), high efficiency (similar to 10(-6)) and high brightness (similar to 10(25) photons.s(-1).mm(-2).mrad(-2) of these Ni-like x-ray lasers make them ideal candidates for x-ray laser applications.

Abstract:

In order to understand the improved performance of Ni-like x-ray lasers driven by a double 75 ps laser pulse, a systematic study on keV emission from plasmas generated by different drive pulse configurations has been made. Significant changes in temperatures and relative abundances of the ionisation stages for different drive pulse configurations have been found with the help of numerical simulations.