An effective optical evaluation technique using visible low-coherence interferometry

An easy and effective path length deviation detection technique is described which uses low-coherent visible light source and Michelson interferometer configuration. This technique uses large-amplitude piezoelectric modulation of a mirror, which probes portions of a complete interferogram. The maximum ambiguity in determining the center position of white light fringes is confined to half the source wavelength. Using this technique, the physical thickness and group index of an optical material are measured with an error around 0-1%. The method of improving the accuracy is also discussed.