We describe a simple spectrometer for sensitive trace gas detection in the atmosphere. A communication laser diode is used as a light source, and a commercial integrating sphere is used as a multipass absorption cell. We developed a theoretical formulation of the relative absorption of the optical power by trace gases in the sphere and applied it to two kinds of experimental result: one that is concerned with a structureless broad absorption band of butane with the use of a 1.2-μm multimode laser diode, and one that is related to the study of an isolated and sharp rovibrational line of water vapor in air at atmospheric pressure with the use of an 830-nm single-mode laser diode. With equivalent path lengths of several meters obtained with a 10-cm-i.d. integrating sphere we can demonstrate the usefulness of such a device as a broadband multipass cell for the measurement of small absorptions.
© 1996 Optical Society of America
Sébastien Tranchart, Ikhlef Hadj Bachir, and Jean-Luc Destombes, "Sensitive trace gas detection with near-infrared laser diodes and an integrating sphere," Appl. Opt. 35, 7070-7074 (1996)