Suppression of Close-Lying Modes in Ring Lasers and Related Devices

Abstract

In ring lasers and certain other devices one is dealing with modes which are split by only very small frequency differences. In general the modes under investigation have the same spatial dependence and thus derive their energy from the same active centers. Due to the shape of the gain‐vs‐frequency curve, the split modes experience a small difference in gain. It is shown that in ring lasers and similar devices one of the modes may thus have much reduced output and may even be so weak as to be unobservable. An experiment is reported in which a longitudinal mode of a Nd³⁺‐doped YAG laser is split into counter‐rotating circularly polarized modes by a Faraday rotator. It is observed that one of the split‐off modes will not even oscillate when the modes are split by a sufficient amount to overcome the locking effects due to intermode scattering.