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Title: 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 H{sub 2}{sup 16}O and H{sub 2}{sup 18}O at 7.12 μm. H{sub 2}{sup 16}O and H{sub 2}{sup 18}O absorption features at 1390.52 cm{sup −1} and 1389.91 cm{sup −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 H{sub 2}{sup 16}O and H{sub 2}{sup 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{sup 18}O isotopic ratio measurement precision of 0.25‰. The ultimate minimum detection limits obtained after 160 s integration time for H{sub 2}{sup 16}O and H{sub 2}{sup 18}O, and δ{sup 18}O measurements were 0.6 ppm, 1.7 ppb, and 0.05‰, respectively.
Authors:
; ;  [1] ;  [2] ; ; ;  [3]
  1. Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)
  2. Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540 (United States)
  3. Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544 (United States)
Publication Date:
OSTI Identifier:
22314441
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ACCURACY; ALGORITHMS; CONCENTRATION RATIO; DEW POINT; ISOTOPE RATIO; LASERS; MIXING RATIO; OXYGEN 16; OXYGEN 18; SENSITIVITY; SPECTROMETERS; TUNING; WATER VAPOR