Interferometric moiré pattern encoded security holograms

Abstract

This paper describes a simple method for making interferometric moire pattern encoded security holograms. These security holograms contain multi-fold concealed and encoded anti-counterfeit security features which can only be decoded by using an encoded key hologram in the final reading process. The concealed codes in these holograms are recorded with an encoded feature, so that they remain invisible to the counterfeiters, thereby enhancing the anti-counterfeiting ability of security holograms. In the final reading process, a specific moire-like fringe pattern is formed on the security hologram only when a reconstructing beam generated from the encoded key hologram illuminates this hologram. Further, a careful spatial filtering results in the generation of a specific moire pattern in the observation plane and it disappears when perfectly repositioned. These can also be used as security codes for better protection against counterfeiting in embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presented.