Zygo interferometer for the precious measurement of tiny refractive index change of two laser crystals

An application of the Zygo system for measuring the refractive index change between two crystals such as 1at%Yb3+: YAG and YAG, was introduced in this paper, having a high accuracy at an order of 10−7. In this method, the tiny refractive index change of two crystals was obtained by measuring the difference in optical path distance of equal thickness interference between two crystals. The mean value of refractive index change of the crystals measured by the Zygo interferometer is 1.10×10−4 for a wavelength of 632.8 nm. And a high accuracy of 3.2×10−6 was achieved.