Passively Q-switched lasers: short pulse duration, single-frequency sources

A rate equation analysis of the passive Q-switching process will be used to develop a design criterion that enables single-frequency, short pulse duration lasers to be built. The analysis will show that the difference in build-up time between any two longitudinal modes of the laser resonator should be comparable to or greater than the laser pulse duration to ensure single frequency operation. In most resonators with lengths <10cm, there is sufficient difference in the build-up times of competing modes to ensure single-frequency operation without the use of intracavity mode-selection elements. For example, a Nd:YAG laser with F₂^-:LiF saturable absorbers ranging in small-signal transmission from 0. 12 to 0.55 was observed to always be single-frequency when operated with a resonator length of 10cm and always be multimode with a 30-cm long resonator