Characteristics of a photoacoustic air pollution detector at CO₂ laser frequencies

Abstract

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

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