A Review of Speckle Photography and Interferometry

Speckling is an interference effect invariably present when highly coherent light is scattered by the different elements of an optically rough surface (roughness ~ " J '" = wavelength). Speckle patterns appear everywhere in space, but interest centres on the image a nd Fourier transform planes. The lateral dime n sion of i ndiv idual speckles is determin ed by the interference of waves from the edges of t h e l i mi ting apertu re a nd is of course the smallest detail to be resolved 1,2. For l arge speckles the correlation becomes too sma l l. Recording speckle patterns in the image, the size of individual speckles is governed by the numerica l aperture of the lens (Fig.l a). By contrast , the speckle size in the Fourier transform plane is limited by the angle of the interfering waves from the edge of the illuminated object field (Fig.l b) . The ,dimension of an individual speckle in the i mage plane is ~ . The speckle size in the Fourier transform p l ane is ~ L where A = wave l ength, D = dimension of pupil, I' = distance from pupil to image plane, b = illuminated object field , L = distance from the object to the Fourier transform plane . Although there are other applications for speckling, two main ones only will be discussed.