Photorefractive surface grating in BaTiO3

We present the theoretical model of a photorefractive surface grating in Z-cut of BaTiO₃ crystal at steady state. Taking the crystal surface to be traction free we consider two cases: (a) dielectric boundary and (b) short-circuited (metallized) boundary. The analysis shows that the photorefractive grating near the crystal boundary has a complex structure. It can be shown that the crystal boundary and the electric boundary conditions have a large influence on the changes in the dielectric tensor induced by a photorefractive grating. Near the crystal surfaces, the changes in the dielectric tensor are different from their volume values, it gives rise to diffraction processes which are forbidden for a bulk grating. One should take elastic contribution into account when calculating the gain expected in photorefractive waveguides or in any case in which light beams travel near the surface of a photorefractive crystal