| 摘要 |
PCT No. PCT/GB92/01115 Sec. 371 Date Jun. 2, 1994 Sec. 102(e) Date Jun. 2, 1994 PCT Filed Jun. 19, 1992 PCT Pub. No. WO93/00224 PCT Pub. Date Jan. 7, 1993A hologram for security markings is provided by a laser transmission hologram (1-4) formed as a surface relief pattern and a coating of a thin metallic layer (5) on the surface relief pattern whereby the hologram is capable of reflecting light from a laser (10). The metallic layer is, preferably, about 500 angstroms thick and the hologram may be mounted on a substrate (7) of an item required to bear the security marking defined by the hologram. In a feature of the invention an apparatus is provided for reading light reflected from the hologram comprising a laser (10) for projecting a beam (9) onto the hologram to be read and a detector (31) and associated logic devices for recognizing a real image of the hologram. The apparatus has the advantage that the laser (10) and detector (31) are both located on the same side of the hologram to be read. |
