Laser Beam Shaping using Self-Focusing in a Nematic Liquid Crystal

A simple and efficient method to convert a Gaussian laser beam into a nearly non-diverging Bessel-like beam or into a thin-walled hollow beam is described. The optical system used for the beam conversion consists of a thin liquid-crystal cell and one or two lenses. At certain parameter values, self-focusing of a Gaussian beam directly results in the formation of a narrow Bessel-like beam, and, if an additional lens is used to collimate the self-focused beam, the collimated beam shows an accurate ring-shaped profile.