Photoelastic Effects in Silicate Glasses

Abstract

The photoelasticity of RnOmSiO2(RnOm=Li2O, Na2O, K2O, and ZnO), Li2O‐Al2O3‐SiO2, Na2O‐Al2O3‐SiO2, and Na2O‐ZnO‐SiO2 glasses was analyzed on the basis of the following equation relating the stress‐optical coefficient and the strain‐optical coefficient: image where C is the stress‐optical coefficient, n is the refractive index, G is the shear modulus, pI2and pI1are the Pockels strain‐optical coefticients, and p and q are the Neumann strain‐optical coefficients. No simple relation was found between the stress‐optical coefficient and the shear modulus, and the factor (p−q) was found to be an essential factor deter‐ mining the stress‐optical coefficient of silicate glasses. It was found that (p−q) decreases markedly with increasing content of modifier oxide, and that the change of (p − q) with composition is governed by the change of the atomic effect, while the lattice effect does not change as much. It is argued that the bridging oxygen with covalent bonds increases the atomic effect and the nonbridging oxygen with ionic bonds reduces the atomic effect.