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Photonics 2016, 3(2), 33; doi:10.3390/photonics3020033

Rapid and Sensitive Quantification of Isotopic Mixtures Using a Rapidly-Swept External Cavity Quantum Cascade Laser

Optical Sensing, Pacific Northwest National Laboratory, Richland, WA 99352, USA
This paper is an extended version of our conference paper presented at Brumfield, B.E.; Taubman, M.S.; Phillips, M.C. Demonstration of a rapidly-swept external cavity quantum cascade laser for rapid and sensitive quantification of chemical mixtures. In Proceedings of the SPIE Conference on Quantum Sensing and Nano Electronics and Photonics XIII, San Francisco, CA, USA, 13 February 2016.
Author to whom correspondence should be addressed.
Received: 31 March 2016 / Revised: 16 May 2016 / Accepted: 17 May 2016 / Published: 23 May 2016
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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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. View Full-Text
Keywords: external cavity quantum cascade laser; infrared spectroscopy; trace-gas sensing external cavity quantum cascade laser; infrared spectroscopy; trace-gas sensing

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Brumfield, B.E.; Taubman, M.S.; Phillips, M.C. Rapid and Sensitive Quantification of Isotopic Mixtures Using a Rapidly-Swept External Cavity Quantum Cascade Laser. Photonics 2016, 3, 33.

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