The dual requirement for high spatial and substance specificity makes stand-off in-theatre biological detection of surface biological contaminants extremely challenging. We will describe a novel combined fluorescence multispectral imaging (MSI) and stand-off Raman approach which are united through their use of deep-UV (sub-250 nm excitation. This allows high-confidence location and classification of candidate contamination sites over the camera field of view, and subsequent resonance-Raman classification of these identified sites. Stand-off Raman is enabled through the use of a novel, extremely high-throughput Spatial Heterodyne spectrometer. The viability of this approach is confirmed through its use on application relevant biological simulant samples.
We report on an investigation addressing the challenge of the rapid detection of in-theatre surface chemical, biological and explosive (CBE) contaminants at a stand-off distance (<1m). The techniques we will describe are fundamentally underpinned by highly characteristic, molecule-specific Raman scattering. The implementation of Raman-at-range is problematic due to the extremely weak scattering cross-sections associated with this process, particularly when undertaken at the near-infrared wavelengths usually mandated by the need to suppress fluorescence. Excitation at shorter (near-UV) wavelengths can result in a two-order increase in scatter and this, combined with the extremely high throughput associated with Spatial Heterodyne Spectrometer (SHS) instrumentation, proves a viable route to Raman-at-range. We then implement time resolved spectral measurements on the ~100ps time scale to exploit the difference in generation timescale associated with Raman scatter and fluorescence generation; once so divorced the characteristics (both temporal and spectral) of the previously-troublesome fluorescent light can be embraced as an additional detection tool. We will show how SHS instrumentation, coupled with low-noise detector technology, can offer over four orders of magnitude improvement in spectral signal-to-noise level compared to conventional Czerny-Turner ‘slitted’ spectrometers using lower-cost linear CCD detectors. Finally, we show how a move to the deep-UV “Resonance-Raman” excitation region of sub- 250nm excitation leads both to enormous improvements in generated Raman signal, and spectral separation of the precious Raman from the troublesome fluorescence signal. We show the viability of this approach with biological spore simulant samples provided by DSTL.
In this paper we present an exploration of the stability and repeatability of a hollow core microstructured fibre (HCMOF) Raman gas sensor. Raman gas detection using HC-MOFs is an exciting technique as it enables high sensitivity, multi-species detection using a small gas volume and within a small physical space. Several previous works have demonstrated the utility of HC-MOF fibres as Raman gas cells for the detection of a wide range of gas species such as methane and hydrogen. Here we take a first look at the Raman signal stability (in a single fibre) and signal reproducibility (from fibre-to-fibre). We show that a HC-MOF Raman system can achieve low within-day variability of 0.3 %CV and fibre-to-fibre variability of 7.6 %CV. Understanding the error within systems such as the one presented is critical in the development of HC-MOF-based gas sensors for practical applications.
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