Lock-In and Intensity-Phase Interaction in the Ring Laser

The lock-in threshold of a single-mode 0.633-μ He–Ne laser was measured. Experiments were performed with a 1:1 mixture of the 20Ne and 22Ne isotope. The lock-in threshold was found to increase with operation of the laser with smaller excess unsaturated gain. Minimum lock-in threshold was found to occur at a higher frequency than the frequency at which the output power was a maximum. A rotational mode competition between the oppositely directed traveling waves was found for rotation rates less than the lock-in threshold. The beam traveling with and against the direction of rotation was found to decrease and increase, respectively, with increasing rotation rate. Analysis showed that the single-mode-ring, laser equations, with mode coupling due to backscattering, satisfactorily explained the experiments.