Extremely sensitive detection of NO_(2) employing off-axis integrated cavity output spectroscopy coupled with multiple-line integrated absorption spectroscopy

摘要

We report on the development of a new sensor for NO_(2) with ultrahigh sensitivity of detection. This has been accomplished by combining off-axis integrated cavity output spectroscopy (OA-ICOS) (which can provide large path lengths of the order of several kilometers in a small volume cell) with multiple-line integrated absorption spectroscopy (MLIAS) (where we integrate the absorption spectra over a large number of rotational-vibrational transitions of the molecular species to further improve the sensitivity). Employing an external cavity quantum cascade laser operating in the 1601-1670 cm~(-1) range and a high-finesse optical cavity, the absorption spectra of NO_(2) over 100 transitions in the R band have been recorded. From the observed linear relationship between the integrated absorption versus concentration of NO_(2) and the standard deviation of the integrated absorption signal, we report an effective sensitivity of detection of approximately 28 ppt (parts in 10~(12)) for NO_(2). To the best of our knowledge, this is among the most sensitive levels of detection of NO_(2) to date.