Explosives detection with a frequency modulation spectrometer.

An explosives detection instrument was designed and tested at SRI International. The instrument uses frequency modulation spectroscopy with midinfrared lead-salt diode lasers to perform high-sensitivity detection of characteristic nitrogen-containing decomposition products of explosives. Ultimately, the instrument should be capable of detecting and identifying subpicogram levels of plastic explosives, which would be suitable for screening passengers at airports. Using the laboratory breadboard instrument and two different explosive vapor generators, we demonstrated a lower limit of detection of 5-10 pg for cyclotrimethylene trinitramine and linearity of the signal over an order of magnitude.