Ultrasensitive CO2 laser photoacoustic system

The present paper describes an extremely sensitive apparatus based upon laser photoacoustic spectroscopy (LPAS) methods which can be used for the detection and measurement of trace gases at very low concentrations (parts per trillion by volume – pptV). Two experimental set-ups were designed and characterized with the photoacoustic (PA) cell in an external configuration: the first one with a low power CO2 laser where the saturation effects are negligible, and a second one with a high power CO2 laser where the saturation effects are important and have to be taken into consideration. In the first case, the minimum detectable concentration was 0.9 ppbV (parts per billion by volume), while in the second case this parameter was improved to 0.29 ppbV. Comparing with the best results published previously in the literature, our minimum detectable concentration is better by a factor of 4.2 in the first case and by a factor of 13.1 in the second case. All measurements were done in nitrogen and ethylene with the 10P(14) line of a continuous wave CO2 laser. This technology can dramatically impact detection in numerous areas.