An electronic speckle-pattern interferometer with a polarization phase-shift technique for the deformation measurement of a diffuse surface is proposed. A common-path optical phase-shift arrangement is
adopted in the interlerometer to improve the stability of the optical system. A polarization phase-shift technique is used to obtain precisely phase-shifted interferograms. A phase map of a fringe pattern, which is capable of distinguishing surface depressions from elevations, can be automatically and accurately obtained from four interferograms by the computer data processing. The numerical data representing the deformation over the entire field can be easily extracted from the phase map. An example of deformation measurement using this interferometer is presented.