Yu, YajunSanchez, Nancy P.Griffin, Robert J.Tittel, Frank K.2016-07-062016-07-062016Yu, Yajun, Sanchez, Nancy P., Griffin, Robert J., et al.. "CW EC-QCL-based sensor for simultaneous detection of H2O, HDO, N2O and CH4ﾠusing multi-pass absorption spectroscopy." <i>Optics Express,</i> 24, no. 10 (2016) The Optical Society: 10391-10401. http://dx.doi.org/10.1364/OE.24.010391.https://hdl.handle.net/1911/90809A sensor system based on a continuous wave, external-cavity quantum-cascade laser (CW EC-QCL) was demonstrated for simultaneous detection of atmospheric H2O, HDO, N2O and CH4using a compact, dense pattern multi-pass gas cell with an effective path-length of 57.6 m. The EC-QCL with a mode-hop-free spectral range of 1225-1285 cm−1 operating at ~7.8 µm was scanned covering four neighboring absorption lines, for H2O at 1281.161 cm−1, HDO at 1281.455 cm−1, N2O at 1281.53 cm−1 and CH4 at 1281.61 cm−1. A first-harmonic-normalized wavelength modulation spectroscopy with second-harmonic detection (WMS-2f/1f) strategy was employed for data processing. An Allan-Werle deviation analysis indicated that minimum detection limits of 1.77 ppmv for H2O, 3.92 ppbv for HDO, 1.43 ppbv for N2O, and 2.2 ppbv for CH4 were achieved with integration times of 50-s, 50-s, 100-s and 129-s, respectively. Experimental measurements of ambient air are also reported.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttp://dx.doi.org/10.1364/OE.24.010391