Single step method for two-frame phase-shifting interferometry with unknown phase shift

Abstract

A procedure to recover the phase from two interferograms with unknown phase step is proposed. A least-square approach is used to solve simultaneously for the illumination background and the introduced phase shift in a local window. This allows to calculate the interferogram phase of the pixel at the center of the window with the standard arc-tangent formula. This process is carried out sequentially across the interferogram field until all pixels are recovered. The proposed scheme is fast and robust, and unlike others methods eliminates the need to implement prior steps of background suppression or interferogram normalization. The developed procedure may be used in problematic environments where vibrations or other disturbances difficult to acquire a full set of phase shifted interferograms with constants phase shifts. The developed procedure is validated in real and simulated data with good results.