A two-tone approach for prolonged readout of multiplexed photorefractive holograms

Photorefractive materials offer important advantages in many optical holography applications, but the recorded images typically remain sensitive to light and therefore erase on readout. Thermal fixing, electrical fixing, two photon absorption during grating formation in the presence of a sensitizing wavelength, and system-level image refreshing procedures have been used to sustain the recorded image during replay. We propose and demonstrate a novel two-tone holography approach that overcomes the unfavorable speed and poor diffraction efficiency of the thermal and electrical fixing, the complexity of refresh techniques, and the high intensities required for two-photon absorption methods. In our two-tone approach, holograms are recorded with short wavelength light, typically in the blue-green spectrum for which the photorefractive material is sensitive, and replayed with longer wavelength light, typically in the red-infrared spectrum, for which the material can be essentially inert. The replay light diffracts off of the recorded gratings, but due to significantly reduced photorefractive sensitivity, it introduces minimal erasure