Beam propagation and optical power limiting with nonlinear media

Abstract

A simple model for absorption and refraction of a laser beam by a bounded nonlinear medium and for diffraction during the beam’s subsequent free-space propagation is used to calculate analytically the steady-state transverse-field profile in the far-field limit using a number of different laser input profiles. Good qualitative agreement with features found in experiments with indium antimonide at cryogenic temperatures is obtained when the input amplitude is assumed to possess a parabolic cross section. Power-transfer curves for a simple and entirely passive power-limiting device operating below the saturation level for nonlinear absorption have been calculated numerically, and it is concluded that the mechanism for limiting is largely determined by the ratio of nonlinear refraction to nonlinear absorption coefficients. Applications to the protection of sensitive optical components are envisaged.