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Interferences and Optical Processing Using Random Diffusers

The phenomenon of interference in diffused light was observed for the first time by Newton. But it is after the discovery of laser and holography that the problem of interference in diffused light gained attention of many workers all over in the world. In the experiment of Burch and Tokarski a number of speckle pattern, displaced laterally relative to one another and recorded successively on the same photographic plate, gives at infinity a system of interferences fringes. We describe a new method of optical processing which is based on the speckle interference phenomenon at infinity. After describing the general principle of the method, we shall give a brief account of the various applications of this technique: extraction of differences between two images, multiplexing of images, the coding and decoding of a message, spatial filtering, data storage. We shall describe also the applications of double-exposure speckle photographs to study displacement and deformation of an object and at the end we shall discuss how speckle intervenes in astronomy.