QEPAS based detection of broadband absorbing molecules using a widely tunable, cw quantum cascade laser at 8.4 μm

Detection of molecules with wide unresolved rotational-vibrational absorption bands is demonstrated by using Quartz Enhanced Photoacoustic Spectroscopy and an amplitude modulated, high power, thermoelectrically cooled quantum cascade laser operating at 8.4 mu m in an external cavity configuration. The laser source exhibits single frequency tuning of 135 cm(-1) with a maximum optical output power of 50 mW. For trace-gas detection of Freon 125 (pentafluoroethane) at 1208.62 cm(-1) a normalized noise equivalent absorption coefficient of NNEA = 2.64 x 10(-9) cm(-1) center dot W/Hz(1/2) was obtained. Noise equivalent sensitivity at ppbv level as well as spectroscopic chemical analysis of a mixture of two broadband absorbers (Freon 125 and acetone) with overlapping absorption spectra were demonstrated. (c) 2007 Optical Society of America.