Wave front dislocations appearance under the laser beam self-action in liquid crystal

We present theoretical study of optical singularity birth and behaviour in an initially smooth wave front of the incident astigmatic Gaussian light beam. Linearly polarised light beam illuminates a homeotropically aligned nematic liquid crystal cell. Strong director anchoring at the cell walls is assumed. Director reorientation profile is found numerically solving Euler-Lagrange equations. We found the threshold intensity for light induced Fredeericksz-type transition. The threshold intensity of light beam is appeared to increase with increasing of beam asymmetry under the constant value of laser beam area and cell thickness. The results are compared with those calculated using Gaussian-like trial function. Utilizing the Huygens-Fresno principle we calculate the propagation of the distorted light beam after the liquid crystal cell. It is found that with distance increasing we can observe at first the dipole, then the quadrupole and then again the dipole of optical vortices whis unit charge. Thus, the trajectory of zero amplitude resembles a deformed rubber ring symmetrical in the xz-, yzplanes and stretched along z-axis.