Expansion of Dynamic Range in Phase-Shifting Interferometry

The paper considers a new method for measuring wave fronts with large curvature. The method is based on the analysis of the trajectory of interference signals (multidimensional Lissajous figures) formed by the intensity values of various points in a series of interferograms obtained by the stepwise phase shift method. The dynamic range is increased by forming the difference phases, similar to the methods of shear interferometry and solving the system of equations equivalent to the system of equations that is obtained when solving the Poisson equation and the Dirichlet boundary conditions. In contrast to classical methods of stepwise phase shift, the proposed method does not require the determination of actual values of phase shifts, which makes it possible to increase the accuracy of measurements and significantly expand the scope of this measurement method. The method is verified by measuring the wave front, which has a height much higher than the wavelength of the laser radiation.