Nitro explosive detection: from basic science to detection at a distance

Standoff detection of landmines has long been central to improve quality of life in a number of countries around the world. A large body of work in the literature focuses on detection of TNT in soil as central to landmine detection. In this presentation, we summarize our efforts toward detection of TNT, from traces to bulk amounts, based on the absorption fingerprint of TNT. Light absorption by TNT is broken into three regions: (1) visible light absorption by TNT, and (2) formation and detection of NO 2 upon UV irradiation of TNT and (3) formation and detection of NO following UV absorption by NO 2 . The absorption spectrum of TNT powder and particles has been determined from spectral analysis of backscattered visible light in traditional optical and near field optical microscopy measurements, respectively. The smallest amount of TNT detected in the near field measurements is 7 femtograms. The absorption spectra of TNT are rich in structure and similar to the one measured for gas phase NO 2 , with lines due to roto vibronic coupling of electronic excited states. Measurements of the backscattered visible light on samples, placed about 5 to 10 meters from the laser source, indicate a clear change in intensity as compared to samples containing TNT. Turning to the second light absorption region, NO 2 is detected upon UV irradiation of solid TNT. NO can also be detected by photolysis of NO 2 .