Standoff detection of VOCs using external cavity quantum cascade laser spectroscopy

Broadband tunable external cavity quantum cascade lasers (ECQCLs) have emerged as attractive laser sources for mid-infrared spectroscopic applications to detect various chemical agents. Here we report on the development of a pulsed, broadband ECQCL-based sensor for open-path sensing multiple volatile organic compounds (VOCs). Instead of using a standard infrared mercury cadmium telluride detector, a quartz crystal tuning fork with a high resonant frequency (similar to 75 kHz) was used as a light detector for laser signal collection. For signal processing, a self-established spectral analysis model integrated with 1D cubic spline interpolation algorithm, multiple linear regression algorithm and fast Fourier transform was developed for quantitative and qualitative analysis of VOC components. The ECQCL sensor was successfully demonstrated for the stand-off detection of three VOCs mixing plume (i.e. ethanol, acetone and diethyl ether) at a distance of 40 m, proving its applicability for leak plumes in security fields.