Proceedings PaperEvaluation of Fizeau interferences: a comparison of phasestepping algorithms
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The signal I of Fizeau interferences observed at two approximately parallel surfaces in reflection is symmetrical in dependence on the interference phase , if the first surface is non-absorbing: (formula available in paper). where = 4nd/X is the interference phase, d the separation of the plates and r1 or r2 the reflection factors of the Fizeau plates. An evaluation of these type of Fizeau interferences by means of a common two-beam algorithm /1/ generates errors even in the case of low reflection factors of uncoated surfaces, which cannot be neglected. These can be reduced for surfaces of low reflectance by means of a modified two-beam algorithm /2/. This approximation is not sufficient in the case of interferences taken from plates with higher reflectance. A new algorithm for symmetrical Fizeau interferences /3/ yields an exact solution of the interference phase independent of the magnitude of the reflectance. Numerical calculations and experimental investigations were carried out, to give an estimation of the deviations, which result from the evaluation of a Fizeau interference with a common two-beam algorithm, and to determine the dependence of the Fizeau algorithm on an imperfect step width of the phase shift.