CHARACTERISTICS OF A PHOTOACOUSTIC AIR-POLLUTION DETECTOR AT CO2-LASER FREQUENCIES

The characteristics of a photoacoustic detection system for measurement of ambient trace atmospheric pollutants at CO2 laser frequencies are analyzed and described. Several photoacoustic variables are optimized in this study. An alternate-traverse acoustic cell to eliminate cell window signals is described. An ac biased 16-cm2 microphone is used. The observed modulation frequency dependence of the acoustic signal and a theoretical analysis are also presented. Trace gas interferents limit the practical sensitivity of the system, however, even with interferents present, a minimum measurable pressure change of 2.43 × 10−9 atm, and apparent absorptivity of 8.42 × 10−9/cm was obtained. Techniques to minimize effects of interferents are reported along with the methodology of the photoacoustic technique in trace gas measurements. © 1979 Optical Society of America.