Resonant enhanced Raman spectroscopy for explosives detection

The resonant Raman cross section for nitromethane, DNT and TNT in vapor phase has been measured in the wavelength range 210-300 nm. The nitromethane cross section was measured at room temperature and at a concentration of 32,500 ppm, whereas the DNT and TNT cross sections were measured in a concentration range of 26 ppm to 1445 ppm at elevated temperatures (81oC-128oC). The measured cross sections indicate the minimum cross section due to some self-absorption. The Raman cross section at or close to resonant wavelengths was found to be in the order of 10-27 to 10-26 cm2str-1 for DNT and TNT, and 8×10-28 cm2str-1 for nitromethane. Thus the resonant Raman cross section for these substances at or near resonant wavelengths is between 2,000 and 100,000 larger than their Raman cross section at 532 nm.