PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY
Security holograms on casino gambling chips. Security holograms are intended to prevent counterfeiting of money and other documents. Since the colour of the image changes with the angle it is viewed at, normal copying methods do not work. Holography uses laser beams to record the dimensions of an object as a set of interference patterns. Shining light on the pattern recreates a holographic image of the object. This technique has been extended to allow digital images to be encoded in holographic diffraction gratings. These are printed on documents as a security feature or brand name.
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