Gain-saturation gratings with an arbitrary diffusion rate of excited states

Gain-saturation gratings, induced by the interaction between the active medium and standing waves in laser cavities, influence the performance of lasers. The modulation depth of the grating is reduced by diffusion of the excitation energy in most host materials, but gain saturation has been modeled only in the limit of strong or weak diffusion. We present an analytical solution of the diffusion equation for two-level systems at an arbitrary diffusion rate. It is shown that for many rare-earth dopants the migration process is not well described by either the weak-or the strong-diffusion approximation. (C) 1998 Optical Society of America.