Detection of explosive materials and their precursors through translucent commercial bottles using spatially offset Raman spectroscopy using excitation wavelength in visible range

The detection and analysis of hazardous materials through opaque barriers is important for law enforcement agencies. Conventional Raman spectroscopy provides fingerprint signatures of materials but lacks the ability to detect materials through opaque containers. Spatially offset Raman spectroscopy (SORS) overcomes the limitation of conventional Raman spectroscopy and allows the detection of materials through most commercial bottles and packaging materials. Moreover, SORS has the potential to detect hazardous materials through colored glass bottles, high-density polyethylene (HDPE) bottles, Teflon layers, etc., which is required in the screening of commercial packaging at airports and other vital facilities. SORS was investigated in the visible range with a 532-nm excitation source for the detection of urea and sodium nitrate through commercial packaging, i.e., a white HDPE bottle with a thickness of 1 mm. The effects of the spatial offset and integration time on the Raman spectra of the contents and container were evaluated. The trend of the change in the relative contributions from the contents and container was studied by varying the offset and integration time. P-nitrobenzoic acid was detected through the colored bottles in the study of reduction of fluorescence in the SORS effect.