Thermal transport studies of 351-nm laser-produced plasmas using extreme ultraviolet spectroscopy

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Abstract
Spectra from an extreme ultraviolet (XUV) grazing incidence spectrograph have been used in the study of thermal transport in laser plasmas. These measurements with XUV lines allowed a diagnosis of much lower temperatures in the heating front than had been previously measured. The OMEGA (24-beam, 351-nm) laser system at the University of Rochester was used to produce plasmas from glass microballoons coated with Al or Ti substrates and overcoated with a plastic ablator. Thermal transport was investigated by measuring the intensity of x-ray and XUV lines as a function of the thickness of the plastic overcoat. These measurements were then compared to the 1D hydrodynamic code lilac. Agreement between the hydrodynamic code and experiment could not be obtained with a reasonable value for the flux limiter ( f≤0.65). Consistent results were reached if nonuniform irradiation and flux inhibition is assumed. The measured burnthrough depths of around 9 μm are similar to previous measurements made with x-ray lines at fluxes below 1015 W/cm2. No evidence of preheat in the heat front was observed.