In-plane displacement and strain measurement by speckle interferometry and moire derivation.

The notion of the coefficient of correlation between two interfering wave fronts is applied to the study of fringe formation and visibility in speckle interferometry. The parameters affecting the visibility of the in-plane displacement fringes are analyzed in the case of an arbitrary displacement and deformation of the object surface. The influence of strain as well as defocusing on the visibility is explicated.