MODE-HOPPING HYSTERESIS IN A SINGLE-FREQUENCY LASER

The mode hops that take place in a single-frequency argon-ion laser as its intracavity etalon is tuned are studied experimentally. The mode hop is shown to occur when the etalon resonance frequency has passed b eyond the half-way point between the two relevant modes. At higher las er powers, it is necessary to tune the etalon even beyond the sub-thre shold mode resonance to induce the mode hop. A theory is presented whi ch explains these hysteresis effects in terms of the gain experienced within the sub-threshold longitudinal modes. The value of this gain is shown to be strongly influenced by a four-wave mixing process which c ouples the sub-threshold modes on either side of the lasing mode.