Effect of optical activity on propagation of two-dimensional spatial solitons in cubic photorefractive crystals

The self-focusing of two-dimensional Gaussian beams in cubic photorefractive optically active crystals of the $\bar1\bar10$ cut in the external electric field arbitrarily oriented in the cut plane is theoretically studied. The ranges of orientation of the external electric field are found in which the divergence of the light beam is smaller than the diffraction divergence. The dependences illustrating the existence of two-dimensional spatial solitons in a 15-mm-thick $Bi_{12}SiO_{20}$ crystal are constructed taking into account the optical activity or neglecting it. The shape of a light beam propagating in the crystal is determined.