Thermal enhancement of diffraction efficiency in cerium doped strontium barium niobate

Although Kukhtarev´s band transport model well describes almost all behavior related to the photorefractive effect, other origins for this effect, such as ZEEPR and polarization gratings, have been reported in recent years. Here, we report an origin which is possibly polarization related, and describe diffraction efficiency enhancement by thermal treatment. The SBN:Ce (cerium doped strontium barium niobate) was grown using the Czochralski method and was polished to optical quality. To pole the crystal, gold was deposited on its c-surfaces and then an electric field of 500kV/m was applied along the c-axis at 95°C. The crystal was then slowly cooled to room temperature in 30 min., and finally the electric field was removed. All the two wave mixing (TWM) experiments were performed in an acrylic box to avoid any air flow that might cause a fringe pattern fluctuation. The 514.5nm line of an Ar ion laser was used and the intensity ratio of reference/object beams was 1.56. Both beams were horizontally polarized to the c-axis and were oriented so that the grating wave vector was parallel to the c-axis. The grating period was 2.34μm. The object beam was set in the energy gaining direction during TWM. The temperature was controlled to an accuracy of 0.1°C with a Peltier cooler positioned below the crystal