Resonant photoacoustic gas sensing by PC-based audio detection

A new and simple technique for data acquisition and processing in an experiment of resonant photoacoustic detection is presented. It is based on the use of the sound card of a desk or laptop computer for digitizing the signal from a microphone enclosed in an acoustical cavity and further processing by a high-resolution fast Fourier transform. The system is applied to the detection of NO₂ traces in air at atmospheric pressure with an amplitude-modulated visible laser and the results are compared with those obtained by a lock-in amplifier. For the same acquisition time the results for the ultimate measurable concentration were 50 ppbV with this system and 130 ppbV with a lock-in amplifier. PACS 42.62.Fi; 82.80.Kq; 43.60.+d