MULTI-SPECTRAL HOLOGRAPHIC SECURITY MARKER, METHOD FOR ITS MANUFACTURE AND HOLOGRAPHIC SECURITY SYSTEM

摘要

A multi-spectral holographic security marker is made by a novel method according to the invention involving a replay frequency shift to one or more final replay frequencies of a part or parts only of a recorded image plane volume hologram. The marker comprises an optional surface hologram and an image plane volume hologram. The volume hologram is divided into discrete areas which have mutually different final replay frequencies. The security information carried by the marker is a combination of the size and shape of those different replay areas together with the hologram content itself which is spread across the different replay areas. If the marker also includes a surface hologram, then that is preferably aligned with the junctions between the replay areas. Preferably one volume hologram replay frequency is in the visible spectrum and the other is in the invisible part of the spectrum (IR or UV).