Dispersion of the Photoelastic Constants of Fused Silica

Abstract

AMONG amorphous substances, vitreous silica occupies a favoured place as it consists of a single chemical constituent. A systematic investigation of the dispersion of its photoelastic constants is therefore of great importance. Filon and Harris¹ measured the stress optical coefficient of fused silica over the range of wave-length 4600–6500 A. Although they reported the presence of dispersion of the stress optic coefficient, the results were not conclusive, for the range of wave-lengths studied by them was restricted. The piezo-optic constants q₁₁ and q₁₂ and the stress optical coefficient have been measured by us for the range of wave-lengths 2250–5700 A. The specimen of fused silica used in the present experiments was obtained from the Thermal Syndicate,Ltd., England. The values of q₁₁ and q₁₂ were determined by measuring the fringe shifts for known additional loads², and the value of C was measured by adopting the method used by Filon and Harris, which was suitably modified to get more accurate results. In both cases a photographic technique was used.