Nonlinear surface optical waves in photorefractive crystals with a diffusion mechanism of nonlinearity

A nonlinear optical phenomenon, namely, the surface waves in photorefractive crystals with a diffusion nonlinearity (of the gradient type), is suggested and analyzed. These waves can be guided along the boundary of the crystal with a metal, a dielectric with a lower average refractive index, or a similar photorefractive crystal with the opposite sign of the diffusion nonlinearity. Our estimates predict that for a typical photorefractive crystal such as ${\mathrm{BaTiO}}_3$ this mechanism can ensure efficient concentration of light power in a crystal layer of ∼10 μm thickness.