GEOMETRICAL OPTIMIZATION OF A LONGITUDINAL RESONANT PHOTOACOUSTIC CELL FOR SENSITIVE AND FAST TRACE GAS-DETECTION

We present a quantitative discussion of the acoustic transmission line theory pertaining to experimental results from a resonant photoacoust ic cell excited in its first longitudinal mode. Window absorption is o ptimally suppressed by buffer volumes and tunable air columns. The aco ustic behavior of an ultrasensitive one inch condenser microphone is q uantitatively described. A small and sensitive photoacoustic cell has been developed for intracavity use in a CO2 waveguide laser permitting measurements of ethylene down to 6 pptv (long term stability 20 pptv) with a time response of 2 s at a trace gas flow of 6 1/h. To demonstr ate the fast time response within a biological application the instant ethylene release of a single tomato is measured. (C) 1996 American In stitute of Physics.