Coherent amplification by multilayer nematic liquid crystal cell

Beam coupling theory for the nonlocal Raman-Nath gratings was developed, which showed that the gain initially increased exponentially with the sample thickness, then deviated from the exponential relation and lowered gradually. It was predicted that large thickness and high intensity sensitivity were simultaneously necessary for the sample to obtain larger gain. The quantitative relation between the signal gain and the sample thickness was investigated experimentally by using a multilayer photorefractive liquid crystal structure to increase the overall interaction length, and the experimental result fitted the theory nicely.