28 June 2016 Absolute air refractive index measurement and tracking based on variable length vacuum cell
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Optical Engineering, 55(6), 064112 (2016). doi:10.1117/1.OE.55.6.064112
A refractometer system using four modified Wu-type heterodyne interferometers with a variable length vacuum cell is presented. The proposed system has two working modes: (1) a moving mode for measuring the absolute air refractive index at the start of a measurement and (2) a static mode for monitoring the air refractive index fluctuation with the same bandwidth as a traditional displacement interferometer. The system requires no gas filling or pumping during the measurement and can be used for real-time refractive index compensation. Comparison experiments with empirical equations are conducted to investigate the feasibility and performance of the proposed system. The standard deviation of the measurement difference between the proposed system and empirical equation is 2.8 parts in 107, which is close to the uncertainty of our refractive index reference based on the accuracy of the environmental sensors. The relative refractive index tracking is a few parts in 108 with a bandwidth of 10 Hz, but high bandwidths are readily achievable.
© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
Xiangzhi Yu, Tieli Zhang, Jonathan D. Ellis, "Absolute air refractive index measurement and tracking based on variable length vacuum cell," Optical Engineering 55(6), 064112 (28 June 2016). https://doi.org/10.1117/1.OE.55.6.064112

Refractive index

Beam splitters

Signal detection


Environmental sensing



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