Carre Phase Shifting Algorithm for Wavelength Scanning Interferometry

Wavelength scanning interferometry is an interferometric technique for measuring surface topography without the well-known 2 pi phase ambiguity limitation. The measurement accuracy and resolution of this technique depends, among other factors, on the algorithm used to evaluate its sinusoidal interference pattern. The widely used fast Fourier transform analysis experiences problems such as waviness error across the measured surface due to spectral leakage. This paper introduces a new fringe analysis method based on the Carre phase shifting algorithm combined with a least squares fitting approach. Numerical simulation was carried out to assess the performance of the Carre algorithm in comparison to fast Fourier transform analysis, and the same was validated by presenting four experimental case study examples (a surface flat, a ceramic ball bearing, a flexible thin film, and a discontinuous step height sample). The analysis results show that the proposed Carre algorithm with least squares fitting can significantly eliminate the waviness error, especially when measuring steep surfaces.

Automated summary

Wavelength scanning interferometry is an interference technique used for measuring surface topography. Compared to the widely used fast Fourier transform analysis, a new fringe analysis method based on the Carre phase shifting algorithm combined with a least squares fitting approach can significantly eliminate waviness error, particularly when measuring steep surfaces.