Examining explosive residues on surfaces with terahertz technology

It is well-known that many explosives have characteristic terahertz (THz) absorption features, and that THz waves can penetrate many dielectric materials. However security applications generally prohibit using THz technology for transmission measurements, either because of standoff distances, thick targets, or opaque targets (metals). As a result, we focus our attention on THz reflection spectroscopy. We have measured the THz reflectivity signature of RDX residues on smooth metal surfaces that contain about 0.4 mg of RDX. We discuss our efforts in detecting trace explosives in reflection as well as our recent results including THz spectroscopy of four explosives from I to 6 THZ, and measurement of the absolute absorption cross-section of explosives.