| 摘要 |
A security device comprising a substrate (1) on or in which is provided a radiation scattering structure derived from a master member (7, Fig. 3), the radiation scattering structure causing an incident, coherent beam of radiation to scatter in a random manner whereby the scattered beams interfere to generate a speckle pattern. The structure may be an embossed pattern or two transparent layers having different refractive indices. Alternatively interference effects can be created by changes of refractive index within the volume of a transmitting material. The device is verified by comparing the speckle pattern with a reference. An auxiliary radiation scattering structure may be used to provide a composite speckle pattern. <IMAGE> |
