Pure-phase iteratively generated Fourier hologram as a security mark

Optically recorded Fourier holograms readable by special laser detectors are frequently used as 'hidden' elements on optically variable devices (OVDs) used for security purpose. However, they are not difficult to identify and reproduce in holographic laboratory. In this paper we propose the use of the phase only computer generated Fourier hologram for security purposes. Its main feature is a possibility of recording a referenceless Fourier hologram which may form a nonsymmetric image. Such an element may be viewed even in the sunlight and it is impossible to manufacture it using standard analog holographic techniques. To obtain the best quality the hologram should be calculated using iterative Fourier-transform algorithm (IFTA) and manufactured using multiple-phase-step or continuous-phase technologies.