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27 August 2014 Nanocrystalline cellulose for optical encryption
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Nanocrystalline cellulose (NCC) exhibits unusual optical properties that make it of interest for hierarchical optical encryption in nanostructured films. The color-travel phenomenon of iridescence is exhibited by NCC when cast as a film from chiral nematic aqueous phase suspensions of the nanocrystals. “Iridescence by self-assembly” has potential for overt encryption as an anti-counterfeiting measure. It also offers an intrinsic level of covert encryption by reflecting leftcircularly polarized light. We show that addition of a UV sensitive dye adds another level of (covert) encryption, and that specially prepared films manifest a rare form of optical non-reciprocity that does not require the application of an external field. Chirality parameters and stokes vector analyses suggest a simple authentication scheme. The method uses a UV light source and a circular polarizer in conjunction with an iridescent feature that can be verified by the eye or by chiral spectrometry.
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Yu Ping Zhang, Karen Allahverdyan, Timothy Morse, Vamsy P. Chodavarapu, Andrew G. Kirk, Tigran Galstian, and Mark P. Andrews "Nanocrystalline cellulose for optical encryption", Proc. SPIE 9172, Nanostructured Thin Films VII, 91720R (27 August 2014);

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