Multi-wavelength phase-shifting interferometry based on a two-step phase-shifting phase retrieval algorithm with a color CMOS

Abstract

By combining the advantage of multi-wavelength phase-shifting interferometry and two-step phase-shifting phase retrieval algorithm, the measured phase with high precision and large measuring range can be retrieved rapidly from three multi-wavelength interferograms with unknown phase shifts recorded by a single-chip color CMOS. First, two normalized differential interferograms without backgrounds are obtained by using the subtraction and then normalization among the three color interferograms. Then the wrapped phases of single wavelength are retrieved by using Gram-Schmidt (GS) orthonormalization approach. Finally the unambiguous phase of the three synthetic wavelengths can be achieved by the subtraction between the wrapped phases of corresponding wavelengths. To reduce the phase noise amplification which introduced by the magnification of wavelengths, the phase unwrapping algorithm of reducing the noise of the three synthetic wavelength to the level of two-synthetic long wavelength, single wavelength, and two-synthetic short wavelength are implemented by turn. Compared with the conventional multi-wavelength phase shifting interferometry, only three interferograms with unknown phase shifts are needed to reconstruct the actual phase of the measured object with high measurement resolution and large measurement range and can be used in dynamic phase measurement. Both simulation and experimental results demonstrate the performance of the proposed method.