Four-frequency emission from a solid-state ring laser

An investigation was made of the feasibility of achieving four-frequency emission from a solid-state ring laser when two modes of different polarizations were emitted in each direction. In this regime the accuracy of measurements of optical nonreciprocal effects was enhanced. It was shown theoretically that this four-frequency regime may be achieved in a solid-state ring laser with a nonplane-plane resonator by intracavity second harmonic generation in a nonlinear element with type II phase matching.