Time-Varying Phenomena in Cavities

Abstract

Sections 6-4 and 6-5 consider the bidirectional ring laser, which is described by two oppositely-running waves of possibly different frequencies. This is a simple and useful example of multimode phenomena that can produce time variations in the laser. The present chapter considers a number of time-varying laser processes such as the relaxation oscillations in the ruby or semiconductor laser output, the build-up of multimode operation in lasers, the generation of steady-state pulse trains, and chaotic operation. Some of these time-varying processes result when you might expect single-mode steady-state operation such as in a homogeneously-broadened unidirectional ring laser. As such their multimode character can be thought of as an instability of single-mode operation. Other cases of multimode operation are expected intuitively, since different cavity modes interact to a considerable extent with different atoms, such as in a Doppler-broadened gaseous medium. While these can also be thought of as optical instabilities, we prefer to refer to them in the traditional way simply as multimode operation. In particular, this kind of operation can produce a periodic train of short pulses.