Spatial-frequency response of photorefractive phase conjugators with Ce : BaTiO3

We propose and demonstrate an interferometric method to measure the spatial-frequency response of photorefractive phase conjugators with Ce:BaTiO3. Two coherent beams are incident on a crystal and form an interference pattern inside the crystal. The two beams undergo stimulated photorefractive backscattering, which creates their corresponding phase conjugations. Then the four waves interact within the crystal. The spatial-frequency resolution of the phase conjugators is measured to be as high as 3750 line pairs/mm by use of the interferometric method. There are several factors that limit the measured spatial resolution when using a U.S. Air Force Resolution Chart. The output modulation deviates from the input modulation for high spatial frequencies. In the presence of a strong additional pump beam, the output modulation of the phase conjugators is almost the same as the input modulation for a wide range of input spatial frequencies. The phase conjugator exhibits a large dynamic range of intensity. We analyze theoretically the modulation transfer function of photorefractive phase conjugators with Ce:BaTiO3 for two mutually coherent beams. The theoretical analysis is in agreement with the experimental results within a small incident-angle region.