Atomistic Theory of Photoelasticity of Cubic Crystals

Abstract

A transparent solid, amorphous or crystalline, exhibits artificial double refraction under the influence of a mechanical stress. A cubic crystal belonging to any of the classes 978-1-4757-0025-1978-1-4757-0025-143m (T _d ), 432 (O), and m3m (O _h ) develops uniaxial birefringence under a stress along a cube normal or cube diagonal. The birefringence produced in the former case involves the differential strain-optical constant (p₁₁ − p₁₂), while that in the latter case involves the strain-optical constant p₄₄. Under a stress in any other direction every cubic crystal becomes biaxial. In all cases the birefringence arises due to the changes brought about by a physical deformation of the crystal in the Lorentz-Lorenz field, the Coulomb field, and the intrinsic polarizabilities of the ions. The theory of photoelasticity has so far been attempted only for cubic crystals because the evaluation of the contributions due to the several changes mentioned above is extremely difficult for crystals of lower symmetry. We give below a brief review of the several theories of the photoelastic effect in cubic crystals.*