Digital Phase Stepping Speckle Interferometry

A digital speckle interferometric technique for deformation measurement using phase stepping and image processing is presented. The object displacements on a 256*256 grid are calculated by subtracting the phases of the speckle field before and after deformation. Accurate phase measurement is achieved by using reference beam phase stepping and digitizing five interferograms to calculate the phase in each detector point. Application of image processing techniques, for instance new phase-unwrapping algorithms, allow measurement of displacements as small as 1 nm and up to 10 000 nm. Results of measurements of out-of-plane deformation of a circular metal plate are shown.