Stable photorefractive square-law conversion using moving grating techniques.

We demonstrate a technique by which the temporal oscillations in the response of a photorefractive square-law converter, a recently developed high-contrast spatial light modulator, may be removed. This technique uses the translation of an amplitude grating incoherently imaged upon a photorefractive crystal to obtain a moving intensity pattern within the material. We thus obtain running-wave effects similar to those seen by previous investigators writing photorefractive gratings by using the interference of two coherent frequency-shifted beams. We show both theoretically and experimentally that the criteria for removing temporal oscillations simultaneously yields a significant improvement in the diffraction efficiency of the square-law converter.