Proceedings PaperPhase shift algorithm for white-light interferometry insensitive to a linear error in phase shift increment (Invited Paper)
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White-light interferometry combined with phase-shift technology becomes a widely used 3-D shape measurement tool in precision engineering. In white-light interference 2π phase ambiguity can be avoided in measurement of optical path difference by searching a modulation peak of light intensity change. This interference surely involves a change in modulation intensity against optical path difference, which is an envelope curve of sinusoidal variations. Then, the phase-shift algorithm by which phase is accurately measured even under the modulation change is required. There is often another requirement that phase shift between captured interferograms would be not restricted to π/2 in the use of the algorithm. Computer simulation has been carried out to estimate phase errors which are retained by applying well-known algorithms to a white-light interference. They are Carre, 4-frame, 5-frame Hariharan, and 7-frame Groot algorithms. All the algorithms have non-negligible errors under the both requirements. Therefore, I extract individual terms (Ii±Ij) in an algorithm equation by considering symmetry of light intensity against phase, where Ij is light intensity just after the j-th shift. Using computer simulation again, I then search for appropriate coefficients by which the terms are multiplied in the equation. I finally have found an algorithm satisfying both the requirements.