Continuous Wave Laser Behavior

Abstract

In previous chapters, we have discussed several features of the components that make up a laser. These are the laser medium itself, whose interaction with an e.m. wave was considered in Chaps. 2 and 3, the passive optical resonator (Chap. 5) and the pumping system (Chap. 6). In this chapter we will make use of results from these earlier chapters to develop the theoretical background required to describe the continuous wave, c.w., laser behavior. The case of transient laser behavior will be considered in the next chapter. The theory developed here uses the so-called rate-equation approximation and the laser equations are derived on the basis of a simple notion that there should be a balance between the total atoms undergoing a transition and total number of photons which are being created or annihilated (1, 2). This theory has the advantage of providing a rather 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 while the e.m. radiation is treated classically, i.e., through Maxwell’s equations) or the full quantum electrodynamics approach (in which both matter and radiation are quantized). We refer the reader elsewhere for these more advanced treatments (3).