Selective optothermal detection of NO2 and H2O with a frequency-tuned CO waveguide laser

Abstract

The results are reported of the CO-laser optothermal (OT) detection of impurity gases when their absorption spectra overlap with those of an interfering gas. The influence of the latter was avoided using low gas pressures corresponding to a maximum of the OT sensitivity. Frequency tuned in the 5.2–6.3 μm wavelength range, 12C16O and 13C16O waveguide lasers were used. The fine frequency tuning at 490 MHz was achieved for 150 laser transitions of both molecules. The OT sensitivity was estimated by NO2 detection in the presence of water vapor. The minimal detectable concentration proved to be 60 ppb at P 19–18(14) transition of a 12C16O laser for NO2 and 75 ppb on P 12–11(13) transition of a 13C16O laser for H2O.