High-gain two-wave mixing in a Ce-SBN photorefractive crystal: large modulation effect and dynamic properties

We have studied two-wave mixing in a Ce-SBN crystal at different pump-to-signal ratios. A small-signal gain coefficient as high as 15.9 cm^-1 at the 633 nm wavelength was obtained. We also observed the pseudo-periodical variation of the two-wave mixing signal with time at different pump-to-signal ratios. The variation is less significant and aperiodic at small pump-to-signal ratios. This time-variation property is a result of the competition between two-wave mixing, beam fanning, as well as modulation due to the Fabry-Perot cavity formed by the crystal surfaces. We have compared the experimental measurements with the theoretical calculation. There is a large discrepancy between the small-signal theory and experimental observations. An improved theory has been developed by taking into account the large-modulation effect. Although the large-signal theory agrees with the experimental results better than the small-signal theory, it still does not precisely describe the two-wave mixing process with the coexistence of various effects