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Liquid silica at high pressure and temperature is shown to undergo significant structural modifications and profound changes in its electronic properties. Temperature measurements on shock waves in silica at 70-1,000 GPa indicate that the specific heat of liquid rises SiO(2) well above the Dulong-Petit limit, exhibiting a broad peak with temperature that is attributable to the growing structural disorder caused by bond breaking in the melt. The simultaneous sharp rise in optical reflectivity of liquid SiO(2) indicates that such dissociation causes the electrical and therefore thermal conductivities of silica to attain metalliclike values of 1-5 x 10(5) S/m and 24-600 W/m x K, respectively.

A study of the properties of multi-MeV proton emission from thin foils following ultraintense laser irradiation has been carried out. It has been shown that the protons are emitted, in a quasilaminar fashion, from a region of transverse size of the order of 100-200 microm. The imaging properties of the proton source are equivalent to those of a much smaller source located several hundred microm in front of the foil. This finding has been obtained by analyzing proton radiographs of periodically structured test objects, and is corroborated by observations of proton emission from laser-heated thick targets.

A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock wave propagation, including high pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh-Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target the instrument measures shock breakout times and Doppler shifts in the reflected light. Velocities of interfaces, free surfaces and of shock fronts traveling through transparent media can be measured for velocities ranging from 0.1 to greater than 50 km/s with accuracies ∼ 1% over most of this range. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneous with the velocity measurements.