Chapter 7 - Nonlinear Optical Processes in Materials

Abstract

The chapter focuses on the nonlinear optical processes in materials and discusses the predominant processes that lead to a nonlinear behavior. It also provides examples of technologically important material systems notable for their NLO (nonlinear optics) properties. Optical nonlinearity is defined as any deviation from the linear relationship between a material's polarization response and an applied electromagnetic field. The nonlinear optical response of materials is utilized in many applications, from optical coupling between fibers to laser light generation and modulation; it is critical to photonic computing and logic operations. The type of nonlinear optical behavior exhibited by each material depends upon its atomic structure and composition. Many different processes can result in an optical nonlinearity in the material response. Most materials exhibit more than one of these processes. In studying optical processes in materials, it is customary to use the semiclassical approach in which photons are treated by the classical form of Maxwell's equations, and electrons and holes are treated quantum mechanically. A nonlinear optical behavior can also be observed in the materials that have permanent polarization anisotropics.