ABSTRACT
Optical wave mixing plays an important role in many interesting and important phenomena in nonlinear media. These include optical two-wave mixing (TWM), four-wave mixing (FWM), stimulated Brillouin scattering (SBS), self-oscillation in photorefractive resonators, self-pumped phase conjugation (SPPC), and mutually pumped phase conjugation (MPPC), etc[l]. In nonlinear media such as photorefractive media (e.g., SBN, BaTi03, KNb03) and Kerr media (e.g., CS2, silica), the presence of optical beams may lead to the formation of an intensity interference pattern. By virtue of the nonlinearity, index gratings are created in these media which may affect the propagation of these optical beams. This is the origin of optical wave mixing in nonlinear media. The wave mixing may lead to beam amplification, depletion, self oscillation, and phase conjugation, etc. In particular, photorefractive effect in some electro-optic crystals can lead to large optical gains as well as to large refractive index changes without requiring high-power lasers. As a result, photorefractive crystals are becoming increasingly important in the field of nonlinear optics [1-4]. In this chapter, we describe the fundamental properties of twowave mixing in photorefractive media. Recent theoretical advances in this area will also be presented and discussed.
