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23 April 2019 Suppression of parasitic gratings with broadband elastomeric light trap
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We present a high performance, removable light trap for the suppression of Fresnel reflections from optical substrates used in holography. When recording holograms with coherent illumination in photosensitive materials, Fresnel reflections lead to undesired interference patterns, producing parasitic gratings. These parasitic gratings consume dynamic range of the material, impact hologram uniformity, and produce stray light on playback. A reflection as small as 4% (glass-air) will produce interference patterns with fringe visibility 0.38. Typical methods for suppressing reflections are often prohibitive in holography, either due to spectral and angular requirements, cost, or potential for contamination. Antireflection-coatings have limited spectral and angular performance, in addition to high cost for one-time use. Relying on polarization suppression of reflections at Brewster’s angle is impractical for the wide range of angles required in most holographic recording applications. Index matching oil with neutral density (ND) filters limit recording orientation and oil often contaminates the samples. We show that by incorporating an absorber into different elastomers, the refractive index of common optical substrates may be matched, and recording light absorbed. Adhesion between the soft elastomer and glass provides sufficient hold while still allowing the layer to be easily removed after use, with no residue or surface damage. Reflection suppression occurs over broad angular and spectral range, with reflected intensity limited only by the index difference between substrate and elastomer. Using carbon black as an absorber, and a poly(dimethylsiloxane) (PDMS) elastomer, we demonstrate a 15 dB reduction of back reflections from a glass slide over a 600 nm bandwidth.
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David B. Miller, Amy C. Sullivan, Izabella R. Berman, and Robert R. McLeod "Suppression of parasitic gratings with broadband elastomeric light trap ", Proc. SPIE 11030, Holography: Advances and Modern Trends VI, 1103009 (23 April 2019);

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