Two-step spatial phase-shifting lateral shearing interferometry by triple gratings

To acquire phase projection information for moiré tomography, a new spatial phase-shifting lateral shearing interferometry is presented in this paper. The system is very simple and contains only three linear gratings and two filters. No wave plates or polarization elements are introduced. Moreover, via using a 4-f system, the optical path is greatly shortened and two complete spatial phase-shifted lateral shearing interferograms can be obtained simultaneously. A corresponding two-step phase-shifting algorithm is used for phase retrieval and the interferometry is used to extract the first-order partial derivative of the spherical wave. The results show that the proposed method is not only feasible but also has high accuracy. Propane flame phase information is measured by the optical system. Finally, error analysis of phase projection extracted by two-step spatial phase-shifting method is mathematically conducted.