Investigations of self-trapped beams in a photorefractive BCT crystal

In this paper, we investigated the beam fanning, self-focusing, and self-defocusing in a photorefractive BCT crystal at an input power of 3 mW for the wavelength of 633 nm without an external electric field and without background illumination. The internal effective coercitive electric field acts for external electric field and the thermal excitation cross-section plays the role of a background illumination. The intensity profile of the beam is smoothed at 65 μm and that the drift mechanism dominates for the beam diameters, which correspond to the symmetrical self-focusing and self-defocusing. The dominant character of the drift mechanism was proven by experiments for two-wave-mixing, whereas there was no energy coupling between interfering beams.