Photoelastic constants of diamond

Summary

All the photoelastic constants of diamond have been determined for the first time. The three stress-optic coefficients areq ₁₁=4·2×10⁻¹¹,q ₁₂=−3·6×10⁻¹¹,q ₄₄=2·6×10⁻¹¹, from which the elasto-optic coefficients have been deduced to bep ₁₁=0·12₅,p ₁₂=−0·32₅,p ₄₄=0·11. It is found thatq ₁₁−q ₁₂ andq ₄₄ are both positive and also that the refractive index of the crystal should decrease when subjected to a hydrostatic pressure, both of which are unique for diamond among the cubic crystals studied so far. In the course of the investigation, a new technique has been developed for determining the absolute path retardation, based on the production of localised interference fringes by the light coming from the two surfaces of the crystal.