PROGRESS IN HOLOGRAPHY

In any plane of an optical tract a coherent light wave is completely described by the complex amplitude, that is to say by a two-valued function. It can, however, also be described by a one-valued or real function such as the intensity or photographic density, plus a known, coherent reference wave. This is the basis of wave-front reconstruction or holography. The history of holography is described, and some of its applications, such as holographic interferometry, contour mapping, and 3D pictures in monochrome or in natural colours. Some prospective applications are holographic panoramas and 3D projection of moving pictures. Information and codage are promising applications but are hampered by the phenomenon of 'laser speckle'. Finally it is pointed out that holography is a multidimensional type of coding, which can transmit more almost independent data than the number of points contained in the hologram.