DECORRELATION AND FRINGE VISIBILITY - ON THE LIMITING BEHAVIOR OF VARIOUS ELECTRONIC SPECKLE-PATTERN CORRELATION INTERFEROMETERS

I discuss the behavior of fringe formation in image-plane electronic speckle-pattern correlation interferometers as the limit of total decorrelation is approached. The interferometers are assumed to operate in the difference mode. The effect of decorrelation will be a decrease in fringe visibility until the limit of total decorrelation, when no fringes will be formed, is reached. A quantitative evaluation of the partially decorrelated fringe pattern is presented for the case of decorrelation due to both tilt and in-plane translation of an object surface element. It is shown that the fringe pattern depends on whether only one or both of the wave fronts forming the primary interferograms suffer from decorrelation. The results are discussed in relation to both in-plane and out-of-plane displacement-sensitive interferometers and to the out-of-plane gradient-sensitive interferometer.