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High-resolution spectral analysis of ammonia near 6.2 μm using a cw EC-QCL coupled with cavity ring-down spectroscopy

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Abstract

We report on the development of a mid-infrared cavity ring-down spectrometer (CRDS) coupled with a continuous wave (cw) external cavity quantum cascade laser (EC-QCL), operating between 6.0 μm and 6.3 μm, for high-resolution spectroscopic studies of ammonia (NH3) which served as a bench-mark molecule in this spectral region. We characterized the EC-QCL based CRDS system in detail and achieved a noise-equivalent absorption (NEA) coefficient of 2.11 × 10−9 cm−1 Hz−1/2 for a 100 Hz data acquisition rate. We thereafter exploited the system for high-resolution spectroscopic analysis of interference-free 10 transition lines of the ν4 fundamental vibrational band of NH3 centred at ∼6.2 μm. We probed the strongest interference-free absorption line RQ(4,3) of ν4, centred at 1613.370 cm−1 for highly-sensitive trace detection of NH3 and subsequently achieved a minimum detection sensitivity (1σ) of 2.78 × 109 molecules per cm3 which translated into the detection limit of 740 parts-per-trillion by volume (pptv/10−12) at a pressure of 115 Torr for an integration time of ∼167 seconds. To demonstrate the efficacy of the present system in real-life applications, we finally measured the mixing ratios of NH3 present in ambient air and human exhaled breath with high sensitivity and molecular specificity.

Graphical abstract: High-resolution spectral analysis of ammonia near 6.2 μm using a cw EC-QCL coupled with cavity ring-down spectroscopy

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Publication details

The article was received on 12 Dec 2017, accepted on 23 Mar 2018 and first published on 23 Mar 2018


Article type: Paper
DOI: 10.1039/C7AN02008B
Citation: Analyst, 2018, Advance Article
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    High-resolution spectral analysis of ammonia near 6.2 μm using a cw EC-QCL coupled with cavity ring-down spectroscopy

    S. Maithani, S. Mandal, A. Maity, M. Pal and M. Pradhan, Analyst, 2018, Advance Article , DOI: 10.1039/C7AN02008B

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