An artist's renditon of a holographic grating.

An artist's rendition of the experimental techniques used for construction of a holographic grating and its application for optical filtering (diffraction) within a photorefractive crystal (see the article by P. R. Schuster et al. in this issue). At the top, two mutually coherent optical beams interfere within the photorefractive material. The spatial intensity distribution caused by the interference leads to a charge migration and ultimately to the production of a refractive index grating (holographic) through the Pockels effect. At the bottom, the application of optical filtering is depicted. A "white" light optical beam made up of many coincident wavelengths enters the photorefractive crystal at an angle that matches the Bragg diffraction conditions for the red wavelength only. The red beam is therefore filtered (diffracted) while the other wavelengths continue to propagate through the crystal undiffracted. Optical filtering is a critical component within a variety of electro-optical systems including remote sensing, imaging (monochromatic), and optical communications. Additional applications for photorefractive materials continue to be identified, such as optical storage, phase conjugation, and optical switching. (Illustration by Kenneth R. Moscati.)

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