Beam self-trapping in a BCT crystal

Self-trapping in photorefractive materials is one of the most investigated effects during the past decade. Usually one utilizes Pockel's effect in photorefractive crystals, whereas the natural divergence of the beam is compensated by the non-linear focusing. The effect depends on beam intensity and polarization, applied electric field, background illumination, crystal geometry, and material properties. In this work we present experimental and numerical investigations of the self-trapping effect in a BCT crystal. Analyzing results of the experiments for fanning, two-wave-mixing, self-focusing and –defocusing as well as investigating the beam profile we found the optimal conditions for generation of self-trapped beams. The experimental results were confirmed by numerical calculations based on both photovoltaic model and model of screening soliton. Light intensity and wavelength were correspondingly 3 mW and 633 nm. No external electric field was applied.