Nonlinear dynamics of a multimode microchip laser due to enhanced stimulated absorption

Abstract

We study the dynamics of a laser oscillating on L optical transitions connecting a common upper level and L lower sublevels. Each transition is single mode. The minimal generalization of the rate equations to explain the experimental observations includes the low-frequency coherence dynamics ͓Europhys. Lett. 45, 307 ͑1999͔͒. These equations are studied analytically. We prove that such a laser has a low intensity self-pulsing threshold corresponding to the destabilization of the lowest of the relaxation oscillation frequencies. It also displays antiphased dynamics in the time-periodic regime, resulting in a vanishingly small oscillation amplitude of the total intensity while modal intensities have finite amplitude oscillations. The physical origin of this behavior is found to be the enhancement of stimulated absorption by quantum interference.