COMPUTER CONTROLLED LASER OPTOACOUSTIC SPECTROSCOPY FOR TRACE GAS ANALYSIS.

Abstract

Optoacoustic spectroscopy is a relatively old technique first described by Alexander Graham Bell in 1881. However, over the intervening years, little use was made of the technique due to its low sensitivity. This was due to low source intensities of available infrared light sources which limited the optoacoustic signal strength. With the advent of laser infrared light sources in the 1960's, there has been a resurgence of interest in optoacoustics. No longer is low source intensity a major limitation to successful optoacoustic spectroscopy. Although adequate infrared light sources are available, the large window background signal observed in all optoacoustic systems has been the major limitation in extending trace gas detection limits to the ppb or sub-ppb level. Similarly, there has been little demonstration of the use of the optoacoustic technique in environments where mixtures of gases are present which have severe spectral overlap. This work will discuss a new windowless cell design that largely eliminates the signal background problem ubiquitous to all presently available optoacoustic cells. New methodologies will be discussed that allow analyses of mixtures to be performed even in cases where spectral overlap is severe. Limitations to both the windowless cell and the various multicomponent analysis strategies are discussed.