Deep Raman spectroscopy for the non-invasive standoff detection of concealed chemical threat agents

► We report deep Raman spctroscopy for the standoff nonivsaive detection of concaeled chemical threat agents. ► We introduce a combined time and space resolve Raman spectrometer for the depth profiling of the therat agents within diffusly scattring pacakging. ► The detection was carried out from a distance of 15m by a single measurement under real life background illuminations within 5s of data acquisition. ► The new spectrometer uses nanosecond laser excitation and nanosecond gated ICCD detection. ► The new spectrometer has strong potential for national security and forensic applications. Deep Raman spectroscopy has been utilized for the standoff detection of concealed chemical threat agents from a distance of 15m under real life background illumination conditions. By using combined time and space resolved measurements, various explosive precursors hidden in opaque plastic containers were identified non-invasively. Our results confirm that combined time and space resolved Raman spectroscopy leads to higher selectivity towards the sub-layer over the surface layer as well as enhanced rejection of fluorescence from the container surface when compared to standoff spatially offset Raman spectroscopy. Raman spectra that have minimal interference from the packaging material and good signal-to-noise ratio were acquired within 5s of measurement time. A new combined time and space resolved Raman spectrometer has been designed with nanosecond laser excitation and gated detection, making it of lower cost and complexity than picosecond-based laboratory systems.