Photopolymer Holograms Top Pira's List of Disruptive Technologies in Security Printing
Photopolymer Holography has undergone some dramatic changes since the original Lippmann type hologram. The principal difference between embossed DOVIDs and holograms recorded in photopolymer is the direction of the interference fringes. In an embossed grating or hologram, minute regular undulations in the surface diffract incident white light into the colours of the rainbow. The surface relief may be in the form of a sinusoidal cross-section, or a triangular ‘saw-tooth’ or a crenelated ‘top-hat’ profile, but they all have to be open structures, so that they can be replicated by embossing. Photopolymer holograms and gratings are typically recorded within the body of the material, so that the light-diffracting fringes are parallel to the surface, like pages in a closed book.