Carré Phase Shifting Algorithm for Wavelength Scanning Interferometry

• Published in: Machines (Basel) Vol. 10; no. 2; p. 116
• Main Authors: Muhamedsalih, Hussam, Tang, Dawei, Kumar, Prashant, Jiang, Xiangqian
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-02-2022
• Subjects: Accuracy; Algorithms; Ball bearings; Carre algorithms; Carré algorithm; Error analysis; Fast Fourier transformations; Fourier transformer; Fringe analysis; Interferometry; Least squares; least squares fitting; Scanning; Silicon wafers; Thin films; Topography; wavelength scanning interferometer; Waviness
• ISSN: 2075-1702; 2075-1702
• DOI: 10.3390/machines10020116

Wavelength scanning interferometry is an interferometric technique for measuring surface topography without the well-known 2π 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 Carré phase shifting algorithm combined with a least squares fitting approach. Numerical simulation was carried out to assess the performance of the Carré 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 Carré algorithm with least squares fitting can significantly eliminate the waviness error, especially when measuring steep surfaces.