Detecting trace quantities of explosives, chemical or biological agents on a variety of surfaces is challenging—especially from a distance without physically collecting a sample. Spectroscopic techniques have been used, but even though they can be highly selective, they have poor sensitivity. Researchers are increasingly using thermal infrared imaging techniques because they can be safely used from a distance.
The concept behind thermal infrared imaging is, when a compound absorbs infrared light, it heats and re-emits most of the absorbed energy at different infrared wavelengths. These emitted wavelengths can be seen by the infrared camera and then analyzed so that the type of explosive can be determined. Researchers at the United States Naval Research Laboratory in Washington, DC, have combined the best of both worlds by pairing thermal imaging with spectroscopy in a Photo-Thermal Infrared Imaging Spectroscopy (PT-IRIS) technology. This photo-thermal infrared approach meets the goals of stand-off detection, which include being eye and skin safe, providing real-time analysis and being adaptable to other types of threats.