An experimental methodology for characterizing the responsivity of the photoacoustic cell for gases at reduced pressure by means of the vibrating strip as the calibrating sound source

Real time, high-sensitivity and interference-free Stark-tuned photoacoustic concentration detection of atmospheric pollutants at CO2 laser wavelengths requires subatmospheric pressures in the cell containing the gaseous sample of interest. The detected photoacoustic signal is in general directly proportional to the cell responsivity, a definition which implies, among the other parameters, the product of the microphone sensitivity and the absorption cross section of the measured species. For correct interpretation of the results it is necessary to determine the dependence of both of these quantities on pressure. A novel effective methodology is proposed, making no use of a test gas and based on a vibrating strip as the calibrating source. Once the cell responsivity has been determined the method described can be used to study the pressure dependence of the absorption cross section of an arbitrary gas.