Spontaneous self-trapping of optical beams in metastable paraelectric crystals

We report on the observation of a new mechanism for self-trapping of optica l beams: self-trapping that stems from spontaneous creation of ferroelectri c crystalline clusters, seeded by a weak photorefractive diffusion field. T his is an evident observation of the highly nonlinear aspects of propagatio n in a thermodynamically metastable system, including optically driven crys talline ordering in a medium undergoing a phase transition.