Covert Laser Readable (CLR) Image
An image in a hologram that is invisible to the naked eye and cannot be viewed with a microscope. It is visualized in laser light with the help of special devices. It is formed when recording a hologram image using the method of electron-beam lithography. A covert laser readable image is an area on the hologram surface which has specific microrelief of 1 micron in size and less than 1 micron in depth. A laser beam, directed perpendicularly to the surface of this area, is reflected from microrelief elements and forms an image on the device screen.
Fig.1. Scheme of observing a covert laser readable image. Incident laser beams (red arrows) and reflected laser beams (green arrows) visualize CLR images
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Fig. 2. Romania. Passport issued in 2017:
a — data page. Polymer substrate; b — the same. Area of CLR image location on the hologram (marked with a frame); c, d — CLR images observed when exposed to a green laser 532 nm. Revealed by the visualizer of CLR images in holograms Regula 2305