Numerical study of self-oscillations in a laser with an unstable cavity

The dynamics of oscillation in a laser with an unstable cavity numerically simulated. The calculations are made in the nonstationary diffraction approximation taking into account the gain saturation in an active medium. The range of parameters in which stationary stable lasing is not reached was found to be considerably wider than the instability region obtained on the basis of the linear analysis of stability of stationary modes. The analysis showed the existence of a self-modulation instability that leads to the generation of a train of short sharp power peaks. The dependence of their repetition period on the gain relaxation time and the excess over the laser threshold was obtained. Doubling and quadrupling of the period of power peaks were found and the conditions providing lasing with the dynamic chaos were determined.