Stabilizing infrared quantum cascade laser beams for standoff detection applications

We are developing a technology for standoff detection of chemicals on surfaces based on active broadband infrared imaging spectroscopy. This approach leverages one or more IR quantum cascade lasers (QCL), tuned to strong absorption bands in the analytes and directed to illuminate an area on a surface of interest. An IR focal plane array is used to image the surface response upon laser illumination. The broadband IR signal is processed as a hyperspectral image cube comprised of spatial, spectral and temporal dimensions as vectors within a detection algorithm. Such standoff spectroscopic imaging applications place stringent stability requirements on the wavelength, power, pulse width and spatial beam profile that pose a challenge for broadly tunable IR QCL. In this manuscript, we discuss methods to mitigate these challenges, including extensive calibration and active feedback stabilization. These mitigation methods should benefit many applications of IR QCL, including those for standoff detection, spectroscopy and imaging.