Coupled Wave Theory for Thick Hologram Gratings

Holographic recording in thick media ("volume recording") is of particular interest for high-capacity information storage, 1-3 for color holography4 and for efficient white-light display of holograms. 5-9 The high efficiency of light conversion which is attainable with thick dielectric holograms is also important for microimaging, and it may make it practical to use holographic optical components (for example, gratings or fly's eye lenses) in a variety of optical systems. In thick holograms it is light diffraction at or near the Bragg angle 2909 2910 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1909 which leads to efficient wavefront reconstruction. This is true for both transmission and reflection holograms, and both types are considered in this paper. The (volume) record of the holographic interference pattern (fringe pattern) usually takes the form of a spatial modulation of the absorption constant or the refractive index of the medium, or both. Modulations of the absorption constant are produced in conventional photographic emulsions and in photochromies, while newer materials, like dichromated gelatin 10,11 lithium niobate,12 or photopolymer materials13 yield modulations of the refractive index. This paper considers the properties of all these types of thick (or "deep") holograms. Of particular interest is their efficiency of converting light into the useful reconstructed wave (diffraction efficiency) and the angular dependence of this diffraction efficiency as the incident light deviates from the Bragg angle.