We report on recent progress applying quantum cascade laser based optical feedback cavity-enhanced absorption spectroscopy in sensing atmospheric methane in the mid-infrared spectral range. An instrument has been built employing a common V-shaped cavity with a powerful continuous-wave distributed feedback quantum cascade laser. The spectrometer has a noise equivalent absorption coefficient of 3.6 ×10−9 cm−1 Hz−1/2 (1σ) for a spectral scan of CH4 at 7.39 µm. From an Allan-Werle analysis of the optical power transmitted by the evacuated cavity a detection limit of 39 parts per trillion of CH4 at atmospheric pressure within 50 s acquisition time was found.
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