ABSTRACT
Nonlinear optics is the study of the interaction of light with matter under conditions such that the linear superposition principle is not valid. The origin of this breakdown of the linear superposition principle can usually be traced to a modification of the optical properties of the material medium induced by the presence of an intense optical field. With a few important exceptions [1], only laser light is sufficiently strong to lead to an appreciable modification of the nonlinear optical properties of a material system and, for this reason, the field of nonlinear optics is basically the study of the interaction of laser light with matter. In this context it is important to distinguish two different sorts of nonlinear optical effects: (1) effects associated with the nonlinear optical response of the material contained within the laser cavity itself; and (2) effects induced by a prescribed laser beam outside of the laser cavity. In this chapter, we are concerned primarily with the second possibility, which constitutes the traditional field of nonlinear optics. Nonlinear optical processes occurring within the laser cavity itself constitute a central aspect of laser physics, as described in chapter A1, and lead to important effects such as laser instabilities and chaos [2] and to self mode locking of lasers [3]. The treatment of nonlinear optics presented in this chapter is necessarily limited in scope. More detailed treatments can be found in various monographs on the subject [4-10] as well as in the research literature. The present treatment follows most closely the notational conventions of [5].
