Novel optical phenomena in near-critical photorefractive crystals: diffusion-driven diffraction and spontaneous self-trapping

We investigate nonlinear optical diffraction in a photorefractive paraelectric, heated slightly above the ferroelectric phase transition. Theoretically, the basic photorefractive band-transport model leads to an anisotropic, nonlinear and nonlocal propagation equation that remarkably allows for explicit analytical solutions, in the form of anisotropic diffraction and noncircular solitons without characteristic length scale. Experiments qualitatively support predictions, but suggest that spontaneous crystal response is present. Actual spontaneous domain formation is experimentally seen to lead to optical self-trapping in both one and two transverse spatial dimensions.