Continuous Wave and Transient Laser Behavior

Abstract

In the previous chapters we have discussed several features of the components which make up a laser. These are the laser medium itself (whose interaction with an e.m. wave was considered in Chapter 2), the pumping system (Chapter 3), and the passive optical resonator (Chapter 4). In this chapter we will make use of the results from earlier chapters in developing the theoretical background necessary for a description of the behavior of a laser both for continuous wave (cw) and transient operation. The theory developed here uses the so-called rate-equation approximation. In this approximation the laser equations are derived on the basis of a simple notion that there should be a balance between the rate of change of total population and total number of laser photons. This theory has the advantage of providing a very simple and intuitive picture of laser behavior. Furthermore, it gives sufficiently accurate results for most practical purposes. For a more refined treatment one should use either the semiclassical approach (in which the matter is quantized and the e.m. waves are treated classically, i.e., by Maxwell’s equations) or the fully quantum approach (in which both matter and fields are quantized). We refer the reader elsewhere for these more advanced treatments.⁽¹⁾