Multiplex coherent anti-Stokes Raman scattering spectroscopy for trace chemical detection.

Trace chemical detection is a particularly challenging problem of significant Army interest. Optical diagnostic techniques offer rapid, accurate, sensitive, and highly selective detection of hazardous materials in a variety of systems. Multiplex coherent anti-stokes Raman scattering (MCARS) spectroscopy generates a complete Raman spectrum from the material of interest using a combination of a supercontinuum pulse, which drives multiple molecular vibrations simultaneously, and a narrowband probe pulse.

Repopulation of nitrogen excited triplet state following laser-induced filamentation.

Laser-induced filamentation was used to study the dynamics of excited molecular nitrogen decay processes. It is well-known that upper excited nitrogen triplet states can be repopulated at time delays far longer than their fluorescence lifetimes. Examination of the time-resolved emission from several different species indicates that there are two major mechanisms acting to repopulate the N2(C(3)Πu) excited state.

Laser-based detection of TNT and RDX residues in real time under ambient conditions.

We detect thin films of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-hexanitro-1,3,5-triazine (RDX) by one- and two-laser photofragmentation-fragment detection spectroscopy in real time at ambient temperature and pressure. In the one-laser technique, a laser tuned to 226 nm excites the energetic material and both generates the characteristic NO photofragments and facilitates their detection by resonance-enhanced multiphoton ionization (REMPI) using their A-X (0,0) transitions near 226 nm. In contrast, in the two-laser technique, a 454 nm laser generates the analyte molecule in the gas phase by matrix-assisted desorption, and a second laser tuned to 226 nm both photofragments it and ionizes the resulting NO.