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Title: Schlieren interferometric concealed coded security holograms
Authors: Kumar, Raj
Aggarwal, A K
Issue Date: May-2007
Publisher: CSIR
IPC Code: G03H
Abstract: A method has been described to create concealed codes in security holograms. The codes are in the form of pure phase patterns and require an interferometric scheme to convert these invisible phase variations into detectable amplitude/intensity variations. An interferometrically encoded reference beam from the key hologram captures a phase modulated object beam to form the security hologram. In the final reading process, a moiré-like fringe pattern gets generated in the observation plane when the same reference beam illuminates security hologram. This moiré pattern is helpful in verifying the genuineness of the hologram and also facilitates in repositioning of security hologram. In the null mode moiré position, true object wavefront gets reconstructed but the information of concealed codes still remains invisible. Use of schlieren technique is proposed as a simple way to reveal the concealed codes for security hologram authentication. These concealed codes can be used as an anti-counterfeiting feature in embossed security holograms.
Page(s): 429-433
ISSN: 0019-5596
Appears in Collections:IJPAP Vol.45(05) [May 2007]

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