<title>Phase singularity born by a Gaussian beam in a nematic liquid crystal cell</title>

Abstract

We present a theoretical study of the possibility of optical singularity birth in a wave front of a laser beam passing through a homeotropically aligned nematic liquid crystal (LC) cell. There is not any distortion in the initial homogeneous homeotropic LC alignment at intensities below some threshold value. When light intensity becomes higher than this threshold value, LC director deviates from its initial orientation. Strong director anchoring at the cell walls is assumed. Inhomogeneous director profile leads to the modulation of refractive index which in its turn may be considered as a Gaussian lens formed in the LC cell. This lens gives birth to the phase singularities in coherent beam with initially smooth wave front. One can find the light field just after the LC cell at small values of director deviation in geometrical optics approximation, and utilizing the Huygens-Fresnel principle calculate spatial position of the phase singularity at near field as a function of intensity of the input beam. It was found that both radius of circular edge dislocation and its distance form the cell boundary decrease with increase of intensity of an incident beam.