Bistable operation and spatial hole burning in multimode lasers containing saturable absorbers

Abstract

Continuous-wave operation of many longitudinal modes with randomly distributed phases in a Fabry-Perot cavity containing a laser medium and a saturable absorber is investigated theoretically. The atomic linewidths of both media are assumed to be homogeneously broadened. The system is described by a coupled set of rate equations including noise terms as well as the dependence of the population difference on the spatial coordinate (along the laser axis) due to standing-wave pattern. The minimum ratio of the saturation intensities of both media which is necessary to get bistability is calculated for different places of the amplifier and the absorber within the cavity and for different spectral widths of the laser field. Due to hole burning which influences the strength of saturation in the media this ratio can vary notably. Moreover, the intensities on the branches of the hysteresis cycles associated with bistable operation are evaluated.