Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Recombining plasmas produced by picosecond laser pulses are characterized by measuring ratio of intensities of resonance lines of H- and He-like ions in the plasmas. It is found that the rapidly recombining plasmas produced by picosecond laser pulses are suitable for high-gain operation.

Abstract:

A theoretical and experimental time-resolved spectroscopic investigation of indirectly driven microsphere implosions is described. The plasma dynamics is studied for several fill gases with a trace amount of argon. Through an analysis of the line profile of Ar XVII 1[Formula Presented]–1s3p[Formula Presented]P, with a line center position at [Formula Presented]=3684 eV, the evolution of the plasma density and temperature as a function of fill gas is examined. The theoretical calculations are performed with a fast computer code, which has been previously benchmarked through the analysis of specific complex ionic spectra in hot dense plasmas. The experimental aspect of the work utilizes the Lawrence Livermore National Laboratory Nova 10 beam laser facility to indirectly drive the implosion of a gas filled plastic microsphere contained in a gold Holhraum target. The dynamical density measurement is derived from a streak camera linewidth measurement and a comparison with the computed profile. Calculations demonstrate that in certain cases there can be a substantial ion dynamics effect on the line shape. The frequency fluctuation model is used to compute the effect on the line profile and a comparison with the experimental spectra provides evidence that ion dynamics may be affecting the line shape. This study provides a method for obtaining an improved understanding of the basic processes dominating the underlying plasma physics of matter compressed to a state of high energy density. © 1996 The American Physical Society.

Abstract:

We report on measurements of a saturated single frequency Ne-like Ge XUV laser on the J = 0->1 transition at 19.6 nm from a refraction compensating double target driven by 150 J of energy from 75 ps Nd-laser pulses. The 19.6 nm line completely dominated the laser output. The output energy was measured to be 0.9 mJ, corresponding to a conversion efficiency of 6x10(-6).

Abstract:

Experimental work with high intensity lasers at the Rutherford Appleton Laboratory has led to the production of both XUV laser and XUV harmonic sources with extreme brightness. In particular an efficient XUV laser source has been developed based on collisionally excited neon -like Ge XXIII(J=0-1) at 19.6 nm using the high power glass laser Vulcan generating 75 ps pulses. With Vulcan operating in sub -ps CPA mode, extremely powerful and short wavelength XUV high harmonic sources have been obtained by irradiation of solid targets and recombinant laser action with high gain has been demonstrated with fibre targets. An ultra-bright Krypton-fluoride laser system, Sprite(recently upgraded to a new configuration Titania) has produced the shortest harmonic wavelength (6.7 nm) and has been used to assess the possibilities of optical field ionised recombinant laser action with gas jet targets. The Ge XUV laser has been successfully applied in fusion research for radiographic measurements of the effect of laser speckle on the hydrodynamic stability of laser accelerated thin foils. The present status of the work, the comparative performance of the XUV laser and harmonic sources and near-term future directions are reviewed.