Sensitive detection of methane and nitrous oxide isotopomers using a continuous wave quantum cascade laser

Abstract

A continuous wave quantum cascade laser (QCL), operating near 8.1 μm, was used for wavelength modulation spectroscopy of methane (CH4) and nitrous oxide (N2O) stable isotopes. Several rotational transitions of 14N216O, 15N14N16O, 14N218O, 14N217O, 13CH4 and 12CH4 fundamental bands were detected. The noise-equivalent absorbance was measured to be less than 10-5 in a 1-Hz bandwidth. A characterization of the laser source was also performed. The use of a QCL spectrometer for high-precision isotope ratio measurements is discussed.