Resonant Photoacoustic simultaneous detection of Methane and ethylene by means of a 1.63 m diode laser

A compact multi-component trace-gas detector based on the resonant photoacoustic technique and a NIR external cavity diode laser has been developed. It has been characterized using a mixture of ethylene and methane diluted in ambient air. A spectroscopic investigation of combination bands and overtones between 5900 and 6250 cm(-1), obtained with an IR pulsed laser photoacoustic spectrometer, allowed us to find a wavelength region where the 2v(3) overtone of CH(4) and the v(5) + v(9) combination band of C(2)H(4) show uncongested rotational lines. Using a single-mode scan of the diode laser in this region, around 6150 cm(-1), the sensitivity for the simultaneous detection of ethylene and methane is 8 ppm/mW and 40 ppm/mW respectively. Factors affecting the sensitivity and selectivity of the detection system and possible improvements suitable to reach the sub-ppm detection limit are discussed.