Rapid and sensitive quantification of isotopic mixtures using a rapidly-swept external cavity quantum cascade laser

Brian E. Brumfield, Matthew S. Taubman, Mark C. Phillips

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13 Scopus citations


A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O liquid near the open-path Herriott cell, allowing the H/D exchange reaction with ambient H2O to produce HDO. Fluctuations in the ratio of D2O and HDO on timescales of < 1 s due to the combined effects of plume transport and the H/D exchange chemical reaction are observed. Noise-equivalent concentrations (1σ) (NEC) of 147.0 ppbv and 151.6 ppbv in a 25-ms measurement time are determined for D2O and HDO, respectively, with a 127-m optical path. These NECs are improved to 23.0 and 24.0 ppbv with a 1-s averaging time for D2O and HDO, respectively. NECs < 200 ppbv are also estimated for N2O, 1,1,1,2-tetrafluoroethane (F134A), CH4, acetone and SO2 for a 25-ms measurement time. The isotopic precision for measurement of the [D2O]/[HDO] concentration ratio of 33‰ and 5‰ is calculated for the current experimental conditions for measurement times of 25 ms and 1 s, respectively.

Original languageEnglish (US)
Article number33
Issue number2
StatePublished - Jun 1 2016
Externally publishedYes


  • External cavity quantum cascade laser
  • Infrared spectroscopy
  • Trace-gas sensing

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Instrumentation
  • Radiology Nuclear Medicine and imaging

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