Dynamics of a Random Laser above Threshold

Abstract

We have performed enhanced backscattering experiments in a high gain random laser, under circumstances where a stationary theory predicts the laser intensity to diverge. Above the laser threshold the observed backscatter cone changes only gradually, not showing any signs of the divergence. We present measurements and theory—generalized laser equations with a diffusive transport term for pump and laser light—to explain the observed behavior. The population dynamics prevent an indefinite growth of the intensity. Time dependence is essential for a theory of random lasers above the laser threshold.