High-Speed Mid-Infrared Hyperspectral Imaging Using Quantum Cascade Lasers

We report on a standoff chemical detection system using widely tunable external-cavity quantum cascade lasers (EC-QCLs) to illuminate target surfaces in the mid infrared (lambda = 7.4 -10.5 mu m). Hyperspectral images (hypercubes) are acquired by synchronously operating the EC-QCLs with a LN2-cooled HgCdTe camera. The use of rapidly tunable lasers and a high-frame-rate camera enables the capture of hypercubes with 128 x 128 pixels and > 100 wavelengths in < 0.1 s. Furthermore, raster scanning of the laser illumination allowed imaging of a 100-cm(2) area at 5-m standoff. Raw hypercubes are post-processed to generate a hypercube that represents the surface reflectance relative to that of a diffuse reflectance standard. Results will be shown for liquids (e.g., silicone oil) and solid particles (e.g., caffeine, acetaminophen) on a variety of surfaces (e.g., aluminum, plastic, glass). Signature spectra are obtained for particulate loadings of RDX on glass of <1 mu g/cm(2).