High-precision diode-laser-based temperature measurement for air refractive index compensation

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http://hdl.handle.net/10138/28118

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Hieta , T , Merimaa , M , Vainio , M , Seppä , J & Lassila , A 2011 , ' High-precision diode-laser-based temperature measurement for air refractive index compensation ' , Applied Optics , vol. 50 , no. 31 , pp. 5990-5998 . https://doi.org/10.1364/AO.50.005990

Title: High-precision diode-laser-based temperature measurement for air refractive index compensation
Author: Hieta, Tuomas; Merimaa, Mikko; Vainio, Markku; Seppä, Jeremias; Lassila, Antti
Contributor: University of Helsinki, Molecular Science
Date: 2011
Language: eng
Number of pages: 9
Belongs to series: Applied Optics
ISSN: 1559-128X
URI: http://hdl.handle.net/10138/28118
Abstract: We present a laser-based system to measure the refractive index of air over a long path length. In optical distance measurements it is essential to know the refractive index of air with high accuracy. Commonly, the refractive index of air is calculated from the properties of the ambient air using either Ciddor or Edlén equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilises direct absorption spectroscopy of oxygen to measure the average temperature of air and of water vapor to measure relative humidity. The method allows measurement of temperature and humidity over the same beam path as in optical distance measurement, providing spatially well matching data. Indoor and outdoor measurements demonstrate the effectiveness of the method. In particular, we demonstrate an effective compensation of the refractive index of air in an interferometric length measurement at a time-variant and spatially non-homogenous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.
Subject: 114 Physical sciences
222 Other engineering and technologies
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