A quantum cascade laser-based water vapor isotope analyzer for environmental monitoring

A field-deployable mid-infrared quantum cascade laser-based spectrometer was designed and developed for measurements of H2(16)O and H2(18)O at 7.12 μm. H2(16)O and H2(18)O absorption features at 1390.52 cm(-1) and 1389.91 cm(-1), respectively, accessible within current tuning range of the laser, wer...

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Bibliographic Details
Published in:Review of scientific instruments 2014-09, Vol.85 (9), p.093103-093103
Main Authors: Wang, W E, Michel, A P M, Wang, L, Tsai, T, Baeck, M L, Smith, J A, Wysocki, G
Format: Article
Language:English
Subjects:
Absorption
ACCURACY
ALGORITHMS
CONCENTRATION RATIO
DEW POINT
Environmental monitoring
Infrared analysis
Infrared lasers
Infrared spectrometers
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ISOTOPE RATIO
Laser applications
LASERS
MIXING RATIO
OXYGEN 16
OXYGEN 18
Quantum cascade lasers
Scientific apparatus & instruments
SENSITIVITY
SPECTROMETERS
TUNING
WATER VAPOR
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Summary:A field-deployable mid-infrared quantum cascade laser-based spectrometer was designed and developed for measurements of H2(16)O and H2(18)O at 7.12 μm. H2(16)O and H2(18)O absorption features at 1390.52 cm(-1) and 1389.91 cm(-1), respectively, accessible within current tuning range of the laser, were targeted. The target lines were carefully selected to assure similar absorption levels and similar temperature sensitivities of the line strength due to comparable lower state energies. A real-time spectral fitting algorithm was implemented for isotopic concentration retrieval. Detection limits for H2(16)O and H2(18)O of 2.2 ppm and 7.0 ppb, respectively, were achieved at a dew point of 14 °C (volume mixing ratio of 15,766 ppm) in 1 s integration time, which resulted in a δ(18)O isotopic ratio measurement precision of 0.25‰. The ultimate minimum detection limits obtained after 160 s integration time for H2(16)O and H2(18)O, and δ(18)O measurements were 0.6 ppm, 1.7 ppb, and 0.05‰, respectively.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.4894161