Interferometry has been a time-honored technique for surface topography measurement. Interferometric measurements of surface shape are relative measurement techniques in which the shape of a known surface is compared with that of an unknown surface, and the difference is displayed as a series of interference fringes. Noise attached in the interference fringes can have catastrophic effects on the phase-unwrapping process, so denoising is essential before reconstruction. Some noise may be generated due to vibrations when multiple images over a finite time period are captured for reconstruction by phase-shifting technique. This harmful noise is drastically reduced when fast phase shifting–based single-shot parallel four-step combined with Fizeau interferometer is applied. Measuring the shape of strongly curved surfaces using two-beam interferometry is very complicated due to the higher fringe density. This problem may be solved by multiple-beam interferometry, thanks to the very sharp interference fringes. The experimental results show the feasibility and high precision of multiple-beam interferometry.
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