We have examined the effect of crystal orientation on ruby R-line shifts under shock compression and tension by measuring shifts in crystals shocked along the ruby a axis and comparing these with the earlier shock data along the c axis and hydrostatic measurements. Additionally, we have extended the theoretical work of Sharma and Gupta [Phys. Rev. B 43, 879 (1991)] on strain-induced shifts of the ruby R lines to permit analysis of R-line shifts for arbitrary deformation. The experimental results show strong anisotropy in R-line shifts for both compression and tension and provide direct evidence of site-symmetry changes under shock loading. The nonlinear increase in ${\mathit{R}}_{1\mathrm{-}}$${\mathit{R}}_2$ splitting for both compression and tension along the a axis is in marked contrast to the c-axis data. Unlike the spectroscopy results, the continuum response of sapphire (or ruby) is isotropic. The theoretical developments permit consistent analyses of all available shock, hydrostatic, and uniaxial-stress-deformation data on R-line shifts.

• Received 28 December 1992

DOI:https://doi.org/10.1103/PhysRevB.48.2929