High-speed simultaneous measurement of refractive index and thickness of transparent plates by low-coherence interferometry and confocal optics

We propose and demonstrate a novel measurement technique for determination of n and t, where the measurement time is only 1 s or less for a thickness of <1 mm. Such a high-speed measurement is successfully achieved by simultaneous detection of coherence-gate and confocal signals with a single scanning of the sample. A measurement accuracy of 0.3% or less was successfully attained for a thickness of <1 mm. A multi-point measurement result is also presented for the index and thickness distributions of a radial-graded-index rod lens.