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- Title
Cavity-enhanced absorption spectroscopy with a red LED source for NO<sub>x</sub> trace analysis.
- Authors
Triki, M.; Cermak, P.; Méjean, G.; Romanini, D.
- Abstract
Incoherent broad-band cavity-enhanced absorption spectroscopy (IBB-CEAS) based on arc lamps has been around for a few years, but only two reports exist using light-emitting diodes (LEDs). We present a setup based on a 643-nm LED which is of interest for the simultaneous detection of NO3 and NO2. The latter is chosen for testing as it is stable and available in calibrated diluted samples. A detection limit in the ppbv range is obtained with 2-min averaging (5×10-9 /cm rms baseline noise level), comparable to the best performance of chemiluminescence devices used for pollution monitoring. At 1-s acquisition time, the detection limit is below 10 ppbv. Extrapolation to NO3 yields a detection limit of a few pptv for a few minutes averaging. We also test the retrieval of absolute sample absorption (and concentration) using the cavity mirror reflectivity obtained with a commercial spectrophotometer, and we conclude that a calibration based on a reference sample of known concentration is preferable for accurate concentration measurements with IBB-CEAS. Finally, we present a rigorous frequency-domain derivation of cavity transmission as a function of wavelength for a broad-band spectrally smooth source, which complements the time-domain derivation by Fiedler et al. This derivation exposes an issue with multiple transverse mode excitation inherent to this technique, which may result in slightly distorted spectral profiles.
- Subjects
ABSORPTION; LIGHT emitting diodes; SPECTRUM analysis; REFLECTANCE; OPTICS
- Publication
Applied Physics B: Lasers & Optics, 2008, Vol 91, Issue 1, p195
- ISSN
0946-2171
- Publication type
Article
- DOI
10.1007/s00340-008-2958-x