Propagation and coherence evolution of optical beams in gain media

Abstract

Abstract An optical beam propagating in a uniform amplifying medium characterized by a linear gain is considered, and the evolution of relevant beam parameters such as spot-size, degree of coherence and radius of curvature is investigated. The analysis relates firstly to Hermite-Gauss (HG) coherent beams and is then extended to partially coherent beams resulting from an arbitrary superposition of HG beams. For all cases, it is found that during propagation in gain media, the spot-size grows more than in free space; furthermore, in the case of partially coherent beams, the global degree of coherence is shown to decrease. These variations are slight for nearly coherent beams but are sizable for highly incoherent beams. Finally, as an example of a class of partially coherent beams, the particularly important case of Gaussian Schell-model beams is considered in detail.