Fringe visibility in lateral displacement measurement from double-exposure laser photographs

The measurement of lateral displacement employing a doubly exposed speckle photograph according to the methods proposed by Archbold et al. and by Butters and Leendertz has been studied. The fringe visibility has been found as a function of the displacement and the resolution of the observing system. The spatial extent of the source has also been considered when a spectral lamp is used in the observing step. The use of an incoherent source replacing the laser in the observing step proved to be of interest because it reduces the speckle in the observed fringes.