Optical quality of high-power laser beams in lenses

Abstract

We analyze the propagation of a high-power laser beam through a lens and calculate the optical beam quality resulting from geometrical aberrations and thermal nonlinearities. We present a general ray-optics formulation, including diffraction effects, for propagation through a nonlinear medium. An analytical expression for the beam quality parameter M2 is derived that includes the lowest-order effects of geometrical and thermal aberrations in a thin lens. A ray-optics simulation, including thermal effects, is used to model propagation through a multilens optical beam expander of the type used in recent long-range, high-power fiber laser experiments.