INDEX OF REFRACTION OF SHOCK-COMPRESSED FUSED-SILICA AND SAPPHIRE

Explicit relations between index of refraction and density are obtained for shock-compressed fused silica and sapphire. The relations are derived from the Doppler-frequency corrections to velocity-interferometry data obtained by Barker and Hollenbach in plate-impact experiments. The index-density relation for sapphire was found using an expression for the Doppler-frequency shift produced by a window material experiencing shock compression. For fused silica, a numerical calculation was required to compute frequency corrections for the combined ramp/shock waveforms produced in the experiments. In both cases the behavior of the refractive index over the density range of the data was found to be predicted quite accurately by adding a correction term to the Gladstone-Dale relation. A particular power-law dependence on density was found for this correction term in each case. The explicit index-density relations permit detailed calculations to be made for index-of-refraction effects from window materials in plate-impact experiments using velocity interferometry. As an example, refractive-index effects are calculated for a fused silica window experiencing a slowly rising compression wave generated in a glass-ceramic material. The present results also permit the polarizability behavior of these materials under shock compression to be examined.