2 and the references therein for a discussion of the trade-offs between these different approaches. 30 – 33 The approach described in this paper is classified as actively illuminated LWIR reflectance spectroscopy. The active illumination techniques can be further classified according to whether they measure the optical reflectance 16 – 29 or the photothermal effect. 11, 12 The LWIR approaches can be divided into those that are passive (utilizing ambient radiation) 13 – 15 and those that are active (utilizing illumination). Of the demonstrated standoff detection methods, the most promising ones include laser-induced breakdown spectroscopy (LIBS), 6, 7 Raman spectroscopy, 8 – 10 and long-wave infrared (LWIR) spectroscopy. 3, 4 However, there are many situations in which physical sampling is not feasible and it is highly desirable to perform noncontact and nondestructive testing at appreciable standoff distances ( > 1 m). 1, 2 Sensitive techniques, such as mass spectrometry and ion-mobility spectrometry, exist for trace chemical sensing, but these require a physical transfer of the chemicals into the instrument. Standoff detection of trace chemicals on surfaces is of great importance for a variety of commercial, law enforcement, intelligence, and military applications, such as explosives detection, drug detection, forensic analysis, contamination avoidance, border protection, cleaning validation, and process monitoring. Examples include the detection of 10 μg of saccharin powder on a wide range of substrates, 0.2 μg of an explosive residue on a computer keyboard, residual pharmaceuticals within a plastic baggie, and a contaminated fingerprint on cell phone case. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology. Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. Results are presented for standoff distances ranging from 0.1 to 25 m. The system is able to generate individual hypercubes in 60 cm 2 / s have been achieved. A trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared.