Spatially offset Raman spectroscopy (SORS) for through-barrier proximal chemical and explosive detection

The capability to detect toxic chemicals and explosive materials through a wide range of container types has a variety of applications, including liquid screening at airport entrance points. Conventional Raman spectroscopy is commonly used for chemical detection, but can result in an intense spectral response due to scattering and/or fluorescence from the container when used for through-barrier applications. Such a response can reduce the effectiveness of the technique for analysis of the container contents by swamping the Raman signature of the target material. By producing two spectra containing different contributions from the container and the contents, spatially offset Raman spectroscopy (SORS) allows a spectrum of the contents to be obtained, even through fluorescing containers. This innovative technique could provide a through-barrier detection capability for a wider range of containers than conventional Raman spectroscopy, including containers made from coloured glass and opaque plastic. In this paper, the use of SORS for through-barrier detection is introduced, and its ability to detect a range of analytes through a range of container materials evaluated. The potential advantages of using a longer excitation wavelength (e.g. 1064 nm) to reduce sample fluorescence are also explored, focussing on target analytes mixed with fluorescent materials.