Abstract:
The self-focusing of Gaussian light beams and the propagation of screening spatial solitons in a cubic optically active photorefractive crystal with the ($\bar1\bar10$) cut plane are studied for an arbitrary orientation of an external electric field in this plane. A change in the rotation of the polarisation plane caused by the nonlinear interaction of light with the crystal is studied theoretically. It is shown that optical activity enhances self-focusing in some cases. Screening self-focusing was observed in an incoherently illuminated $Bi_{12}SiO_{20}$ crystal without additional laser irradiation. The experimental data well agree with the proposed theoretical model.