Beam self-trapping in a BCT crystal

We present some aspects of wave self-focusing and self-defocusing in a photorefractive Ba 0.77 Ca 0.23 TiO 3 (BCT) crystal without external electric field and without background illumination. The effects depend on the cross-section of the input beam. We show that by decreasing of the diameter of the input beam from 730 μm the fanning effect disappears at 150 μm. A symmetrical self-focusing is observed for input diameters from 150 μm down to 40 μm and a symmetrical self-defocusing for input diameters from 40 μm down to 20 μm. The ID self-trapping is detected at 65 μm in BCT. Light power and wavelength are correspondingly 3 mW and 633 nm. The experimental results are supplemented with numerical calculations based on both photovoltaic model and model of screening soliton.