Subota S. Gaussian beam self-action in nematic liquid crystal

The thesis is devoted to the theoretical study of optical singularities birth in the wave front of laser beam, which passes through a homeotropically oriented nematic liquid crystal cell. Director anchoring at the cell walls was assumed to be strong. The phenomenon of liquid crystal director reorientation has been found to display a threshold character. An original analytical expression has been derived for the threshold intensity of director reorientation for the case of Gaussian light beam. The results obtained by these two methods of free energy minimization have been compared. It has been shown that Gaussian trial function can be used for certain values of parameters in order to essentially reduce the calculation time. The solutions of Maxwell’s equations for slightly anisotropic inhomogeneous liquid crystal have been found in quasiisotropic and geometrical optics approximations. The inhomogeneous director profile may cause phase singularity appearances in the coherent light beam with initially smooth wave front. The amplitude and phase of the distorted light beam at different distances from the cell wall was calculated by utilizing the Huygens-Fresnel principle. It turned out that in the case of stigmatic Gaussian beam a circular edge dislocation appears. The zero-amplitude trajectory in the case of astigmatic Gaussian beam self-action resembles a deformed rubber ring symmetrical in the xz-, yz- planes and stretched along the direction of light beam propagation.