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Optical Engineering

Absolute air refractive index measurement and tracking based on variable length vacuum cell
Author(s): Xiangzhi Yu; Tieli Zhang; Jonathan D. Ellis
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Paper Abstract

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.

Paper Details

Date Published: 28 June 2016
PDF: 6 pages
Opt. Eng. 55(6) 064112 doi: 10.1117/1.OE.55.6.064112
Published in: Optical Engineering Volume 55, Issue 6
Show Author Affiliations
Xiangzhi Yu, Univ. of Rochester (United States)
Tieli Zhang, Univ. of Rochester (United States)
Beijing Aerospace Institute for Metrology & Measurement Technology (China)
Jonathan D. Ellis, Univ. of Rochester (United States)

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