Optimization of the photorefractive properties of BaTiO3

Abstract

Photorefractive materials offer great promise for a variety of applications in adaptive optics and optical data processing. BaTiO3 is a particularly promising material, primarily because the very large value of the electrooptic tensor component r42 yields correspondingly large values of grating efficiency, beam coupling gain, and four-wave mixing reflectivity. At present, commercial samples of BaTiO3 have a relatively long photorefractive respone time, typically 0.1-1.0 s at an intensity of 1 W/cm2. For many applications, response times <1 ms are needed. To develop techniques for improving the response time and other photorefractive properties, it is first necessary to understand the physical origins of the photorefractive effect in BaTiO3. We begin by reviewing recent experiments intended to identify the photorefractive centers in BaTiO3 and to measure their concentrations. We also review energy level models which have been proposed, as well as the corresponding charge compensation relations. The two basic approaches to improving the response time in BaTiO3 are doping during growth and treatment of existing crystals in a reducing atmosphere. We analyze the influence of both of these approaches on the respone time and describe the results of recent experiments on both doped and reduced crystals.