Contribution of thermoelastic stresses to the temperature coefficient of the refractive index dn/dT of cubic crystals

The approximation of planar strains and the method of successive approximations are used to solve the equilibrium equations for cubic crystals heated inhomogeneously by a narrow axisymmetric laser beam. The change in the refractive index Δn is calculated for NaCl, KCl, LiF, KBr, and KJ crystals. It is shown that the change Δn induced on the beam axis by thermoelastic stresses represents up to 50% of the value of Δn in the case of free homogeneous heating of a crystal.