Sensitive Detection Of Hydrogen Chloride By Derivative Spectroscopy With A Diode Laser

P. Pokrowsky; W. Herrmann

doi:10.1117/12.965812

8 September 1981 Sensitive Detection Of Hydrogen Chloride By Derivative Spectroscopy With A Diode Laser

P. Pokrowsky, W. Herrmann

Author Affiliations +

Proceedings Volume 0286, Laser Spectroscopy for Sensitive Detection; (1981) https://doi.org/10.1117/12.965812
Event: 1981 Technical Symposium East, 1981, Washington, D.C., United States

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.

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P. Pokrowsky and W. Herrmann "Sensitive Detection Of Hydrogen Chloride By Derivative Spectroscopy With A Diode Laser", Proc. SPIE 0286, Laser Spectroscopy for Sensitive Detection, (8 September 1981); https://doi.org/10.1117/12.965812

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