Photoelastic constants of diamond

Abstract

All the photoelastic constants of diamond have been determined for the first time. The three stress-optic coefficients are q₁₁=4·2×10^-11, q₁₂=-3·6×10^-11, q₄₄=2·6×10^-11, from which the elasto-optic coefficients have been deduced to be p₁₁=0·12₅, p₁₂=-0·32₅, p₄₄=0·11. It is found that q₁₁-q₁₂ and q₄₄ 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.