Differential mode excitation photoacoustic spectroscopy: a new photoacoustic detection scheme.

A robust and simple gas sensor based on a novel photoacoustic scheme named "differential mode excitation photoacoustic spectroscopy (DME-PAS)" is presented. This method takes advantage of the selective excitation of two different modes in a resonant photoacoustic cell. A blackbody light source is used for simplicity in combination with optical correlation to provide a good selectivity. The frequency response of the proposed resonant cell is modeled using the extended Helmholtz resonator theory. The DME-PAS device is tested using acetone vapor and a model developed to describe its response when the gas concentration is varied. The obtained limit of detection is 25 ppm m(-1) for acetone in room air. Using DME-PAS, the derived gas concentration is affected neither by intensity fluctuations of the light source nor by any microphone drifts.