The recording of holograms in which the reference beam enters through the supporting substrate involves attenuation factors which differ strongly between signal and reference. This paper addresses the issue of fringe contrast under these extreme conditions and provides quantitative data that are indicative of at least a partial solution to the problem. We define a spatial average for the fringe contrast and offer results which follow our theoretical model for Du Pont OmniDexTM photopolymers. The direct edge referenced technique for recording is re-visited with observation of a new phenomenon which we call self-induced index matching. An alternative fringe recording geometry is proposed and compared with direct recording.
An edge-lit holographic optical element has been developed which produces a high contrast and high resolution fingerprint image. Continuing work on the development of a holographic optical element for use in a compact fingerprint imaging system is described. The hologram is combined with an electronic imaging array into a package only several millimeters thick, using no image transfer lens system. Previously reported results with green holograms are reviewed. New results are presented for red holograms illuminated by a laser diode. Design issues and experimental results are discussed, relating to selection of hologram operating wavelength, angular and wavelength sensitivity of the hologram, and image quality versus packaging volume tradeoffs.
Holography as a science owes its success to the recording of interference patterns in a variety of recording materials. Many of these materials are also used in the companion science of precision lithography. This paper discusses two important areas of holography and lithography. Both make use of the novel imaging polymers of DuPont. We discuss here the manufacture of micro-diffusers for diverse optical applications and the creation of phase holograms by contact lithographic methods using silver image amplitude holograms. Such copying methods are essentially incoherent using broad band UV light and bridge the gap between holography and lithography.
This paper looks at some ideas old and new that relate to the formation of images in dichromated gelatin. The traditional view that the dichromated system hardens gelatin thus preventing solubilization of the material must be balanced against other observations such as that of the reduction of the bulk index of the gelatin layer and the appearance of gelatin in the processing solutions. We revisit the problem and take a look at some new chemical ideas that relate to the behavior of gelatin during bleaching of silver halides. A new method for the processing of silver halide-sensitized gelatin (S.H.S.G.) is proposed which endows the silver halide emulsion with more than three orders of magnitude of speed when compared with D.C.G. per se.
Some rigorous statements are made about the recording of holograms in the true edge- illuminated geometry. An essential asymmetry is outlined between the role of the substrate refractive index and that of the recording medium. Laboratory observations indicate that unique possibilities exist for recording in this regime using the photopolymers of Du Pont. Unlike any other regime of holography, numerous optical criteria have to be met simultaneously. We believe that self-induced index matching between the recording polymer layer and the substrate on which it is mounted is the key to a workable recording system.
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