Photorefractive Properties and Applications of Barium Titanate and Tungsten Bronze Ferroelectrics

This thesis is an experimental and theoretical investigation of the photorefractive properties of barium titanate and tungsten bronze ferroelectrics, and applications thereof. In the first part, the physics of the photorefractive effect is presented. The band transport equations are solved for three cases that describe the photorefractive mechanism in a crystal with one photorefractive species and either one or two types of charge carriers, or in a crystal with two photorefractive species, but only one type of charge carrier. In the second part, the coupled wave theory of two-wave mixing in photorefractive crystals is reviewed. Effects of energy coupling between the two interacting beams are discussed along with experimental methods for determining the two-beam coupling coefficient and the photorefractive response time. The photorefractive crystals barium titanate, strontium barium niobate, and barium strontium potassium sodium niobate are described in the third part. A summary of their optical, physical and electrical properties is presented for use in subsequent sections of the thesis. In the fourth part, the photorefractive properties of these crystals are presented. Data from two-beam coupling experiments are used to obtain the two-beam coupling coefficients and the photorefractive response times of the crystals under a variety of experimental conditions. The band transport models are then applied to these results. Figures of merit are defined in the fifth part that are then used in a comparison of several photorefractive materials, including the barium titanate, the strontium barium niobate, and the barium strontium potassium sodium niobate crystals. Both ferroelectric and non-ferroelectric materials are considered. In the last part, applications using barium titanate and the tungsten bronze ferroelectrics are described. By using the self-focusing properties of barium titanate and strontium barium niobate, the compensation of nonlinear optical distortions with phase conjugation is demonstrated. A passive phase conjugator that relies on no external mirrors and uses strontium barium niobate as the nonlinear medium is also described. Finally, a thresholding passive phase conjugate mirror is then presented along with several devices that can perform mathematical operations on images such as subtraction and differentiation.