TEMPERATURE-DEPENDENCE OF 2-BEAM COUPLING AND DARK DECAY IN PHOTOREFRACTIVE BATIO3

The temperature dependence of two-beam coupling and dark decay in phot orefractive BaTiO3 is reported. We show that the competition between d eep and shallow traps depends on temperature and writing intensity, an d influences two-beam coupling and dark decay. The dynamics of dark de cay, characterized by a fast decay of partial erasure and a subsequent slow decay, is influenced by the presence of deep and shallow traps. Partial erasure, due to thermal excitation of charges from the shallow traps, decreases with temperature and increases with writing intensit y. The time constant of the slow decay, due to thermal excitation of c harges from the deep traps, depends strongly on temperature, but not o n the writing intensity. At room temperature, the existence of deep an d shallow trap leads to intensity-dependent photorefractive gains. As temperature increases, the influence from the shallow trap decreases, and the photorefractive gain becomes independent of the intensity. How ever, at much higher temperatures (similar to 100 degrees C), the phot orefractive gain resumes its dependence on intensity due to an increas e in dark conductivity at elevated temperature.