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Proceedings Paper

Sensitive Detection Of Hydrogen Chloride By Derivative Spectroscopy With A Diode Laser
Author(s): P. Pokrowsky; W. Herrmann
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Paper Abstract

Low concentration pollutants in the atmosphere can be detected by their infrared absorption spectrum. We use a diode laser spectrometer in a dual beam configuration for this purpose. The laser source is frequency modulated to provide the sensitivity enhancement associated with derivative spectroscopy. One of the laser beams is passed through a reference cell containing the gas to be detected in order to lock the laser frequency to the center of the absorption line. The other beam passes through a White cell with 64 in absorption path length. Sample air is sucked through this cell at a pressure of about 100 mbar. Although the pressure reduction reduces the density of absorbing molecules by a factor of ten, the increase in absorption cross section due to the norrowing linewidth nearly compensates this effect and drastically reduces interference from other gases. The absorption is observed as a modulation of the laser intensity at twice the modulation frequency. The intensity modulation is proportional to the second derivative of the absorption line. The spectrometer was used in a field experiment on board a research vessel in the North Sea for the measurement of HC] in the plume of incineration ships. An HC1 detection sensitivity of 100 ppb1/Hz was achieved.

Paper Details

Date Published: 8 September 1981
PDF: 7 pages
Proc. SPIE 0286, Laser Spectroscopy for Sensitive Detection, (8 September 1981); doi: 10.1117/12.965812
Show Author Affiliations
P. Pokrowsky, Insmut fur Physik, GKSS-Forscnungszentrum Geestnacht GmbH (West Germany)
W. Herrmann, Insmut fur Physik, GKSS-Forscnungszentrum Geesthacht GmbH (West Germany)

Published in SPIE Proceedings Vol. 0286:
Laser Spectroscopy for Sensitive Detection
Jerry A. Gelbwachs, Editor(s)

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