Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho

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121 Scopus citations

Abstract

A quantum-cascade laser operating at a wavelength of 8.1 μm 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 v4 P branch were recorded. The measured laser linewidth was 50 MHz. A CH4 concentration of 15.6 parts in 106 (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 × 10-4. The content of 13CH4 and CH3D species in a CH4 sample was determined.

Original languageEnglish (US)
Pages (from-to)1762-1764
Number of pages3
JournalOptics Letters
Volume24
Issue number23
DOIs
StatePublished - Dec 1 1999

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics

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