Photorefractive properties of ferroelectric materials for optical phase conjugation, two-beam coupling, and holographic storage.

摘要

The results of a systematic investigation of doped strontium barium niobate and potassium tantalate niobate for photorefractive beam coupling and optical holographic storage are presented in this thesis. Methods that were successfully employed to increase the magnitude of the photorefractive effect and speed up the response of these materials are also presented. Applications in the area of optical phase conjugation, distortion correction, limiting, and thresholding are also discussed.;In the first part, the equations governing the photorefractive effect through band transport are introduced. The solutions giving the internal space charge field in photorefractive materials are presented for the one carrier, one species model that approximates the process in strontium barium niobate and most other materials. The coupled equations describing the two-beam coupling effect are also derived.;Next, the results of experiments using as-grown potassium tantalate niobate for holographic diffraction and strontium barium niobate for two-beam coupling are presented. With KTN, the effect of Nb concentration on the phase transition, temperature dependence of diffraction efficiency and dark storage time, and the effects of the bias electric field are discussed. With SBN, the effect of dopant type, temperature dependence of the photorefractive effect, the effects of dark conductivity in Cr-doped SBN:60, and wavelength dependence are presented.;The third part describes methods and results of increasing the magnitude of the photorefractive effect in SBN. Optimization of the grating period, oxidation and reduction heat treatments, temperature control, and applied fields are discussed. Significant increases in the two-beam coupling constant were observed in Cr-doped SBN:60 with applied fields of up to 10 kV/cm. An order of magnitude reduction of the response time in Rh-doped SBN:60 has been achieved with an applied field of 10 kV/cm.;The final part discusses applications of these materials, particularly in the areas of phase conjugation, distortion correction, and optical signal processing. A total internal reflection phase conjugate mirror using SBN instead of BaTiO