Instabilities leading to self-pulsing, hysteresis, and chaos in a multimode laser

A numerical model which treats lasers as spatially extended systems with discrete elements is used to describe processes which cause instabilities in standing wave lasers. The stability of steady-state solutions for a CW laser model is examined. Instabilities are shown to arise from nutation oscillations and interactions between counterpropagating waves and gain and loss inhomogeneities in the cavity. The coherence of the field and the partial filling of the cavity by the active medium allow the formation of periodic structures, i.e., the inhomogeneities, in the inversion. The instabilities take the form of an uneven longitudinal distribution of radiation in the laser, as well as spatially separated elements and intensity differences among counterpropagating waves. Approaches which might be successful for numerical simulations with stable solutions for nonlinear oscillator systems are indicated.