White-light Phase-stepping Interferometry: Measurement of the Fractional Interference Order

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Abstract
Intensity data obtained with white light and an achromatic phase shifter in an interferometric surface profiler can be used to locate the peak of the visibility curve as the test surface is moved in steps along the height axis. We show that the same intensity data can also be used to find the fractional interference order at each point on the test surface, at the position of the test surface nearest to the visibility peak and, hence, its height at that point, with a high degree of accuracy.