Spectrally resolved interferometry to measure thickness and refractive index of transparent material

We demonstrate a method for simultaneous measurement of thickness and refractive index of transparent materials based on spectrally-resolved interferometry. By extracting the phase from the interference spectrum, the measured optical path difference can be obtained directly without phase shift device in the measurable range. This unique advantage makes it capable of measuring physical thickness and refractive index by introducing transparent medium and processing three useful optical path differences. In the long-term stability test, the repeatability experiment of spectral resolution interferometric ranging technology using femtosecond laser is carried out within 60 min, and the standard deviation is 341nm.