Electromechanical and optical effects in photorefractive materials

From thermodynamic considerations, we derive a consistent set of equations coupling the steady-state photoinduced photorefractive space-charge field t o mechanical deformations, de permittivity, and refractive index changes. F or the first time to our knowledge, these equations include piezoelectricit y, electrostriction, the elasto-optic effect, the linear and quadratic elec tro-optic effects, as well as the influence of the volume forces and electr ic torques. We determine the conditions on the material parameters, for whi ch volume forces and torques are of some importance on the optical properti es. These equations resulting from a macroscopic approach an valid whatever the physical microscopic origins of the various effects. Non centrosymmetrical and centrosymmetrical materials are considered. The order of approximation is the lowest possible able to describe the mentioned effects in both type s of materials.