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  • Title: Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser.
    Author: Kosterev AA, Curl RF, Tittel FK, Gmachl C, Capasso F, Sivco DL, Baillargeon JN, Hutchinson AL, Cho AY.
    Journal: Opt Lett; 1999 Dec 01; 24(23):1762-4. PubMed ID: 11543189.
    Abstract:
    A quantum-cascade laser operating at a wavelength of 8.1 micrometers was used for high-sensitivity absorption spectroscopy of methane (CH4). The laser frequency was continuously scanned with current over more than 3 cm-1, and absorption spectra of the CH4 nu 4 P branch were recorded. The measured laser linewidth was 50 MHz. A CH4 concentration of 15.6 parts in 10(6) ( ppm) in 50 Torr of air was measured in a 43-cm path length with +/- 0.5-ppm accuracy when the signal was averaged over 400 scans. The minimum detectable absorption in such direct absorption measurements is estimated to be 1.1 x 10(-4). The content of 13CH4 and CH3D species in a CH4 sample was determined.
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