Multi-spectral holographic security marker, method for its manufacture and holographic security system

A multi-spectral holographic security marker 2 comprises an image plane volume hologram recorded in a polymeric pressure and light sensitive film data carrier, with one hologram area a having a first replay frequency (wavelength) and one or more other areas b having a further, different replay frequency (wavelength); the different frequencies may be in the visible and invisible (ultraviolet (UV) or infrared (IR)) bands. A surface, pressure imprinted, hologram 3 may also be present. The different frequency response holographic areas may be formed by differentially compressing regions a and b, thus distorting Bragg planes (shown as curved lines); thus, even if initially recorded with a single volume hologram, different multi spectral regions may be formed by distortion, e.g. by means of a die (10, Figure 3). Security information carried by the marker is a combination of the size and shape of different colour/frequency replay areas together with the hologram content itself which is spread across the different replay areas.