External cavity quantum cascade laser-based QEPAS for chlorodifluoromethane spectroscopy and sensing

摘要

Detection of chlorodifluoromethane (R-22) with unresolved rotational-vibrational absorption lines was demonstrated using quartz-enhanced photoacoustic spectroscopy (QEPAS) and an external cavity quantum cascade laser (EC-QCL). A spectral region spanning 1230-1420cm(-1) was measured. A mini quartz tuning fork with high resonance frequency of75kHz is first used to improve the QEPAS sensitivity. At a laser optical power of 2mW, a 1 sigma-normalized noise-equivalent absorption of 1.9x10(-8)cm(-1)WHz(-1/2) was achieved. The analysis of a mixture of two broadband absorbers (R-22 and acetone) with overlapping absorption spectra was demonstrated. The good linearity response of the measured QEPAS signal amplitude as a function of R-22 concentration indicates the QEPAS-based sensor has a great potential for continuous and noninvasive real-time monitoring of broadband absorbers.