Spatial-frequency response of photorefractive phase conjugators with Ce:BaTiO_3

Abstract

We propose and demonstrate an interferometric method to measure thespatial-frequency response of photorefractive phase conjugators withCe:BaTiO(3). Two coherent beams are incident on a crystaland form an interference pattern inside the crystal. The two beamsundergo stimulated photorefractive backscattering, which creates theircorresponding phase conjugations. Then the four waves interactwithin the crystal. The spatial-frequency resolution of the phaseconjugators is measured to be as high as 3750 line pairs/mm by use ofthe interferometric method. There are several factors that limitthe measured spatial resolution when using a U.S. Air Force ResolutionChart. The output modulation deviates from the input modulation forhigh spatial frequencies. In the presence of a strong additionalpump beam, the output modulation of the phase conjugators is almost thesame as the input modulation for a wide range of input spatialfrequencies. The phase conjugator exhibits a large dynamic range ofintensity. We analyze theoretically the modulation transferfunction of photorefractive phase conjugators withCe:BaTiO(3) for two mutually coherent beams. Thetheoretical analysis is in agreement with the experimental resultswithin a small incident-angle region.