Nitroexplosives detection: from basic science to detection at a distance

In this contribution, 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) VIS light absorption by TNT, and (2) formation and detection of NO₂ upon UV irradiation of TNT and (3) formation and detection of NO following UV absorption by NO₂. The absorption spectrum of TNT powder and particles has been determined from spectral analysis of backscattered VIS light in traditional optical and near field optical microscopy measurements, respectively. The smallest amount of TNT detected in the near field measurements is 7 fg. The absorption spectra of TNT are rich in structure and similar to the one measured for gas phase NO₂, with lines due to rovibronic 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. The second light absorption region, NO₂ is detected upon UV irradiation of solid TNT.