Saturation dynamics and working limits of saturated absorption cavity ringdown spectroscopy.

Sadiek, I. and Friedrichs, Gernot (2016) Saturation dynamics and working limits of saturated absorption cavity ringdown spectroscopy. Physical Chemistry Chemical Physics, 18 (33). pp. 22978-22989. DOI 10.1039/C6CP01966H.

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Cavity ringdown spectroscopy (CRDS) in the linear absorption regime is a well-established method for sensitive trace gas detection, but only a few studies have addressed quantitative measurements in the presence of a saturated sample. In fact, saturation is usually avoided in order to escape from the required complex modeling of the saturation process that depends on the characteristics of the absorbing species, its interaction with the surrounding gas as well as on the temporal and spectral characteristics of the cavity excitation. Conversely, the novel saturated-absorption cavity ringdown spectroscopy approach (SCAR/Sat-CRDS) takes advantage of sample saturation in order to allow one to extract both the gas absorption and the empty cavity loss rates from a single ringdown event. Using a new continuous-wave infrared CRD spectrometer equipped with a tunable narrow-bandwidth highpower OPO laser system and a 18 bit digitizer, the transient dynamics of absorption saturation and the working limits of the Sat-CRDS approach in terms of its ability to extract reliable trace gas concentrations have been experimentally studied in this work. Using a strong methane transition as a test case, the excitation power P-0 and saturation power PS have been systematically varied to explore a wide range of saturation regimes. At pressures 5 mu bar < p < 2 mbar, the saturation intensity revealed a nearly linear pressure dependence showing that non-collisional processes contribute to the overall relaxation. A ratio of P-0/PS approximate to 15 turned out to be optimal with working limits of 5 < P-0/P-S < 300. Moreover, the ratio of the absorption and empty cavity loss rates, gamma(g)/gamma(c), has been varied to test the dynamic range of the method. At gamma(g) > gamma(c), a pronounced coupling between the two parameters has been observed. Finally, a standard error analysis was performed revealing that the Sat-CRDS approach holds its advantages over conventional CRDS implementations in particular when the attainable ultimate detection sensitivity is limited by uncertainties in the empty cavity ringdown constant.

Document Type: Article
Additional Information: Times Cited: 0 Sadiek, Ibrahim Friedrichs, Gernot
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R07
Kiel University
Kiel University > Kiel Marine Science
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1039/C6CP01966H
ISSN: 1463-9076
Projects: Future Ocean
Date Deposited: 16 Mar 2017 07:57
Last Modified: 23 Sep 2019 23:11

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