Robust retrieval of optical surfaces phase maps in sub-Nyquist multi-wavelength interferometry

This paper reports on phase retrieval method in non-nulling dual-wavelength interferometry. It uses synthetic phase as shape estimation for determination of fringe orders within every pixel. The fringe order map is subsequently used for unwrapping of phase measured at shorter wavelengths. It was experimentally shown that even for inaccurate synthetic phase, the computed phase for short wavelength is correct. The key point is in analysis of phase fields in spatial derivatives where the sensitivity to phase distortions is lower instead of analyzing the phase fields themselves.