Simultaneous thickness variation and surface profiling of glass plates using Fizeau interferometer with elimination of offset phase error

Fringe analysis using phase modulation through wavelength scanning is extensively utilized for profiling the surface and thickness variation of glass plates. However, the nonlinearity of the phase-modulation error during wavelength scanning causes an offset error in the calculated phase. Therefore, in this research, two types of 19-frame phase-extraction formulas were derived for simultaneous profiling of the thickness variation and surface of a glass plate, focusing on eliminating the offset phase error. These new formulas were visualized in the frequency domain using the Fourier description. The ability of these formulas to eliminate the offset error was confirmed through numerical error analysis. Finally, the surface and thickness variation of a glass plate were simultaneously profiled using the large-aperture Fizeau interferometer and the new 19-frame formulas. The standard deviations obtained for thickness variation and surface profiling were 4.687 and 14.421 nm, respectively, which were lower than those obtained when using other phase-extraction formulas.

Automated summary

In this study, two 19-frame phase extraction formulas were derived to simultaneously measure the thickness variation and surface profile of glass plates, effectively eliminating offset phase errors. The Fourier description in the frequency domain was utilized to visualize the new formulas, and numerical error analysis confirmed their ability to eliminate offset errors. Using these new formulas with a large-aperture Fizeau interferometer, the standard deviations for thickness variation and surface profiling were lower compared to other phase extraction methods.