Mode selection in CW laser with homogeneously broadened gain

The gain calculated for a laser with ring and Fabry-Perot resonators respectively is given in a general formulation which shows clearly the influence of the spatially inhomogeneous saturation due to the standing wave pattern and the resulting Bragg scattering. When selecting a single mode in a Fabry-Perot resonator, the losses necessary to quench the modes are equal to those losses which the selected mode suffers due to the self-induced Bragg grating in the active medium. In a unidirectional ring laser, the losses only need exceed the gain of additional separate gain reservoirs of the modes. Also possible reasons are dealt with which cause stable bidirectional operation in a ring laser with homogeneously broadened gain.