| 摘要 |
An optical device for security and anti-counterfeit applications comprises a diffractive structure comprising a discrete region that in response to white light illumination generates an image by a process of diffraction in close angular proximity to the specular reflection and which is thus substantially non-visible to an observer, and which under coherent illumination generates a laser projection covert image which forms an image in an image plane located away from the physical plane of the device and which is angularly co-located in close proximity to the direction and position of the specular reflection.
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