Piezobirefringence and Deformation Potentials of the Alkali Halides

Abstract

We have measured the stress-induced birefringence of KI, RbI, CsI, KBr, RbBr, and CsBr in the ultraviolet at room temperature. The stress-optical constants obtained show strong dispersion in the vicinity of the absorption edge. A theoretical analysis of this dispersion yields the shear deformation potentials of the edge exciton; such deformation potentials are difficult to obtain in conventional measurements because of plastic flow. The signs of the deformation potentials for [100] stress are opposite to those of [111] stress. For a given stress direction, these signs reverse in going from NaCl- to CsCl-structure materials. A model calculation which accounts for the signs and magnitudes of these deformation potentials is presented.