Micrometer-scale rigid-body translations are determined from electronic speckle interferometric fringe patterns. An iterative minimum error procedure employs the relative fringe order of picked positions of fringe maxima and minima within a single interferogram to calculate the displacement field directly. The method does not calculate the displacement at a single point but relies on the assumption that the character, but not the magnitudes or directions, of the displacements over the viewing area of the interferogram is known. That is, a model of the displacements exists. On perfect, noise-free forward modeled fringe patterns calculated for an 8.0-μm displacement, the phase error is less than 2 × 10-6 fringe orders (1.3 × 10-5 rad) and probably results only from numerical noise in the inversion. On real fringe patterns obtained in electronic speckle interferometric experiments, mean phase errors are generally less than 5 × 10-5 fringe orders (3.2 × 10-4 rad), suggesting that the technique is robust despite errors resulting from speckle noise, lack of accuracy in positioning of experimental components, and image-distortion corrections.
© 1998 Optical Society of AmericaPDF Article