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

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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 utilizes 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 nonhomogeneous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using a 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.
Original languageEnglish
Pages (from-to)5990 - 5998
JournalApplied Optics
Volume50
Issue number31
DOIs
Publication statusPublished - 2011
MoE publication typeA1 Journal article-refereed

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Temperature measurement
temperature measurement
Semiconductor lasers
Refractive index
semiconductor lasers
refractivity
air
Air
Distance measurement
humidity
Atmospheric humidity
Temperature
temperature
Compensation and Redress
Absorption spectroscopy
Water vapor
water vapor
absorption spectroscopy
Oxygen
Lasers

Cite this

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title = "High-precision diode-laser-based temperature measurement for air refractive index compensation",
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 Edl{\'e}n equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilizes 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 nonhomogeneous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using a 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.",
author = "Tuomas Hieta and Mikko Merimaa and Markku Vainio and Jeremias Sepp{\"a} and Antti Lassila",
year = "2011",
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language = "English",
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journal = "Applied Optics",
issn = "1559-128X",
publisher = "Optical Society of America OSA",
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High-precision diode-laser-based temperature measurement for air refractive index compensation. / Hieta, Tuomas; Merimaa, Mikko; Vainio, Markku; Seppä, Jeremias; Lassila, Antti.

In: Applied Optics, Vol. 50, No. 31, 2011, p. 5990 - 5998.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - High-precision diode-laser-based temperature measurement for air refractive index compensation

AU - Hieta, Tuomas

AU - Merimaa, Mikko

AU - Vainio, Markku

AU - Seppä, Jeremias

AU - Lassila, Antti

PY - 2011

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AB - 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 utilizes 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 nonhomogeneous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using a 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.

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