Practical speckle interferometry for measuring in-plane deformation

Speckle interferometry involves making a high resolution double-exposure photograph of an object that is illuminated with coherent light. When observed in a Fourier optical data processor, fringes are observed that are indicative of the changes, such as displacements, occurring in the body between exposures. Sensitivity of the measurement is variable and may be chosen after the data are recorded. A simple calibration procedure is described and its use in measuring in-plane displacements in deformable solids is demonstrated. Also given are some limitations on the range of sensitivity that can be effectively utilized with holographic films, simple procedures, and a small laser.