Stacks of layers with periodical corrugations of interfaces as devices for document security

Protection of documents against tampering and counterfeiting can be accomplished by visually identifiable devices. A key requirement for them is that they should provide unique features enabling verification of authenticity. In stacks of layers with periodic undulations, diffraction and interference effects can be combined together with excitation of guided modes and long-range plasmons to provide large security potential. The studied stacks are composed of a hot-stamped HRI embossing foil, with or without a thin metal film deposited on the foil HRI coating, and they are embossed with diffraction gratings. Designs of stacks are analysed by dedicated numerical methods, with the gratings having sinusoidal profiles of the same modulation depth at each internal interface of the stack. The designs take into account aspects of practical producibility of final foil devices via embossing and vacuum deposition techniques. Corresponding experimentally realized samples are tested by angular and spectroscopic scatterometry.