Optical polarization effects in a gas laser

Any book on classical optics has an important chapter on the characteristics of polarized light and its propagation in physical media. Experiments with polarizedlight have also greatly contributed to the understanding of the structure of atoms, molecules and matter. The advent of the laser has brought about a revival of optics,· mainly because it made available light sources of extremely high intensities and very high temporal and spatial coherence. This article deals with the interaction of laser light with the medium in which it is generated arid in particular with the optical polarization effects produced by this interaction. The first of the following three sections contains a general exposition of the main concepts of laser physics useful for the understanding of the rest of the article. The next section deals with the information that can be obtained from the experimental study of polarization effects in a gas laser. It reveals unorthodox optical behaviour of the generating medium and the section contains a phenomenological description in classical terms. The last section gives the basic elements of a quantitative description. It indicates how a quantummechanical theory leads to a detailed understanding of the observations and to some unique predictions which are confirmed by experiment.