Photoacoustic detection of ozone using a quantum cascade laser

A 9.5-mum pulsed quantum cascade laser (QCL) and a differential photoacoustic (PA) detector were used to measure trace concentrations of similar to100 ppbv ozone at ambient pressure with high selectivity. The QCL was tuned by temperature variation between -41 degreesC and 30.6 degreesC and the corresponding wavelengths were determined by the PA spectrum of CO2. Good agreement was found between the measured PA spectrum and the simulated HITRAN spectrum of ozone. The PA signal showed a linear dependence on the ozone concentration in the investigated 4300-100 ppbv range. In comparison with recently published results, in which a similar QCL in combination with an optical absorption analysis technique was applied, an improvement in the ozone-detection sensitivity by a factor of about 200 was achieved.