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Open AccessArticle

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

1
School of Computer Software, Tianjin University, Tianjin 300072, China
2
National Ocean Technology Center, Tianjin 300112, China
3
School of Marine Science and Technology, Tianjin University, Tianjin 300072, China
*
Author to whom correspondence should be addressed.
Sensors 2018, 18(4), 1143; https://doi.org/10.3390/s18041143
Received: 16 March 2018 / Revised: 5 April 2018 / Accepted: 5 April 2018 / Published: 9 April 2018
(This article belongs to the Section Physical Sensors)
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 10−5 level has been achieved, compared with the values calculated by the empirical formula. View Full-Text
Keywords: refractive index of water; frequency comb; interferometry; metrology refractive index of water; frequency comb; interferometry; metrology
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MDPI and ACS Style

Meng, Z.; Zhai, X.; Wei, J.; Wang, Z.; Wu, H. Absolute Measurement of the Refractive Index of Water by a Mode-Locked Laser at 518 nm. Sensors 2018, 18, 1143.

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