Abstract

A saturable absorber inside the laser cavity induces self-pulsation instability in the single-mode laser oscillation (passive Q-switching, PQS). Since PQS instability requires no bad-cavity condition and is caused just above the laser threshold, it is realized much more easily than other single-mode instabilities associated with the Lorenz-Haken¹ and Casparson² instabilities. An infrared gas laser has a lot of controllable parameters that are variable for a wide range, and so it is quite a useful system to study various features of passive Q-switching systematically. PQS pulse structure is critically dependent on the dynamical properties of the molecular systems. Also it is possible to obtain quantitative data on the dynamical constants from the analysis of the PQS behavior. PQS in CO₂ lasers has been extensively studied thus far. Several rate-equation models^3,4,5 were successfully applied to describe the observed characteristics of PQS. Especially the so-called three-level: two-level model^4,5 reproduces even complicated PQS pulses to the detailed pulse structures.

© 1988 Optical Society of America