Loss Lock-In in the Ring Laser

In the ring laser, frequency synchronization between the oppositely directed traveling waves is usually attributed to mutual coupling by the mechanism of the backscattering of energy from each of the beams into the direction of the other. A new type of coupling is introduced where the standing wave state is shown to have less losses than the traveling wave state for rotations rates less than some critical lock-in threshold. The coupling mechanism is spacially varying losses over the cavity length. The minimum loss condition is also shown to determine the location of the nodes of the standing waves. In certain cases, lock-in thresholds due to nonuniform losses are shown to have the potential of being a few orders-of-magnitude greater than thresholds attributed to backscattering.