Tomsk State University of Control Systems and Rad , Russia

The basic physical principles of the interaction of two counterpropagating light beams on dynamic reflection holograms recorded in the Denisyuk scheme in single-crystals due to the diffusion formation of space-charge field are considered. We analyze the nonlinear response relating to both phase (photorefractive) and amplitude (absorption) components of the reflection grating. Along with conventional linear electro-optic effect the additional elasto-optic contributions to the phase grating induced by secondary phenomena are taken into account. We consider two converse effects, piezoelectric and flexoelectric ones, as the causes of existence of the elastic-strain gratings in the single-crystal materials. It was shown that qualitative distinctions in photorefractive response induced by linear electro-optic effect and by converse flexoelectric effect together with the elasto-optic one are exhibited at phase demodulation in an adaptive interferometric setup utilizing interaction of two counterpropagating light beams on the reflection holograms. Based on the experiments with such interaction in the (100)-cut Bi12TiO20:Fe,Cu crystals we established that theirs flexoelectric coefficient f11 can be estimated as the value in the range from 1.9 to 5.3 nC/m.