Nonlinear Optical Principles and the Photorefractive Effect Applied to Optical Phase Conjugation

摘要

This thesis presents a detailed interpretation of published theory of nonlinear optical phase conjugation by degenerate four wave mixing and by the photorefractive effect. Photorefractive phase conjugation is shown to be a low incident intensity alternative to degenerate four wave mixing (which requires high intensity incident light to achieve the nonlinear polarization of a medium. The derivations of two models for the photorefractive effect, Feinberg's Hopping Model and Kukhtarev's Solid State Model, are presented. The significance of Kukhtarev's model is his development of criteria for which spatially sinusoidal incident light (interference fringes) produces a spatially sinusoidal electro-static field in the crystal-an assumption casually made in much photorefractive work. Both models culminate in expressions for the magnitude of the space-charge field and the spatial phase shift between the field and the incident interference pattern for small modulation conditions. Feinberg's model is extended to develop expressions for two-beam coupling, diffraction efficiency and phase conjugate reflectivity. An alternative development for these expressions assumes the electro-static field exists in the crystal and modulates the crystal's refractive index by the linear electro-optic (Pockel's) effect.