Absolute Measurement of the Refractive Index of Water by a Mode-Locked Laser at 518 nm

• Published in: Sensors (Basel, Switzerland) Vol. 18; no. 4; p. 1143
• Main Authors: Meng, Zhaopeng, Zhai, Xiaoyu, Wei, Jianguo, Wang, Zhiyang, Wu, Hanzhong
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 09.04.2018; MDPI
• Subjects: Containers; frequency comb; interferometry; metrology; refractive index of water; Refractivity; Thermal expansion; frequency comb; metrology; refractive index of water; interferometry
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s18041143

In this paper, we demonstrate a method using a frequency comb, which can precisely measure the refractive index of water. We have developed a simple system, in which a Michelson interferometer is placed into a quartz-glass container with a low expansion coefficient, and for which compensation of the thermal expansion of the water container is not required. By scanning a mirror on a moving stage, a pair of cross-correlation patterns can be generated. We can obtain the length information via these cross-correlation patterns, with or without water in the container. The refractive index of water can be measured by the resulting lengths. Long-term experimental results show that our method can measure the refractive index of water with a high degree of accuracy-measurement uncertainty at 10 level has been achieved, compared with the values calculated by the empirical formula.