Center Wavelength Measurement based on Higher Steps Phase-shifting Algorithms in White-light Scanning Interferometry

Traditionally, monochromatic wavelength interferometry is applied to the measurement of smooth surfaces. Owing to the phase ambiguity, the range of depth measurement with a monochromatic light source is limited. To overcome this problem, with the fact that white-light source is continuous in spectrum, the white-light scanning interferometry (WLSI) can be used to measure discontinuous profile. In this paper, envelope function based on local linear conditions was developed and WLSI using higher steps phase-shifting algorithms (PSAs) was proposed. Maximum intensity peak positions at five points were used to calculate the center wavelength of the light source by both phase unwrapping and linear least-squares fitting. Both simulated and experimental results showed that the proposed PSAs have good linearity and robustness to accurately measure center wavelength of the white-light source