Reorientation of nematic liquid crystal under the action of light with stygmatic and astygmatic Gaussian profile

We report on theoretical study of optical singularity birth in a wave front of light beam with stigmatic and astigmatic Gaussian profile with intially smooth wave front passing through a homeotropically aligned nematic liquid crystal (NLC) cell. When a linearly polarized astigmatic Gaussian light beam illuminates the cell, the light induced Frederick's transition can be observed. Strong director anchoring at the cell walls is assumed. Ritz's variational method is used, i.e. the profile of director reorientation is considered to be similar to astigmatic Gaussian profile. Parameters of the trial function are calculated numerically. The threshold intensity of light beam is appeared to increase with increasing of asymmetry of the beam under the constant value of laser beam area and cell thickness. Utilizing the Huygens-Fresnel principle and geometrical optics approximation we calculate the amplitude distribution in space for different distances from the cell. It is obtained that in the case of stygmatic Gaussian beam incidence on NLC cell the circular edge dislocation is born.