Nonlinear Piezo-Optic Behavior of Sphalerite (α-ZnS)

Abstract
The variation of the refractive index of sphalerite with pressure to 7 kbar has been determined by an interferometric method. The refractive index decreases with increasing pressure, as was predicted earlier. Above 3 kbar the change in refractive index is found to be nonlinear with respect to both stress and strain, thus demonstrating that Pockels's linear elasto- and piezo-optic equations have to be extended.