Holographic determination of in-plane deformation

The paper describes a method for determining the displacement component in a chosen direction on the surface of a deformed object. The method is based on hologram interferometry and uses two illumination waves. During reconstruction, two families of interference fringes are formed; the moiré fringes formed by the superposition of those two families are loci of equal displacement, measured along a direction perpendicular on the bisector of the two illumination waves. By properly choosing the illuminating directions, it is possible to form a moiré pattern corresponding to the in-plane displacements of a flat specimen. Although in the present state of the art applications of the method are confined to the laboratory, it is thought it will provide a simple tool for research in studying small deformations. Some experimental applications verifying the theory are presented.