Abstract
We report on the development of a new sensor for 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 range and a high-finesse optical cavity, the absorption spectra of over 100 transitions in the R band have been recorded. From the observed linear relationship between the integrated absorption versus concentration of and the standard deviation of the integrated absorption signal, we report an effective sensitivity of detection of approximately (parts in ) for . To the best of our knowledge, this is among the most sensitive levels of detection of to date.
© 2011 Optical Society of America
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