We demonstrate how molecular spectroscopy methods using NIR and MIR lasers can provide rapid detection and
identification of many threat materials. It is increasingly recognised that one spectroscopic method will not be suited to
every target in every scenario, both in terms of spectroscopic selectivity and the context e.g. vapour phase or within a
sealed container. The orthogonal selection rules and capabilities of IR and Raman in combination allow the identification
of a very broad range of targets, both in liquid and vapour phase. Therefore, we introduce the benefits of the combining
infra-red absorbance based on Quantum Cascade lasers (QC-IR) and NIR Raman spectroscopy for nitrogenous and
peroxide based materials. Rapid scan rates up to 10Hz for QC-IR and Raman and are demonstrated using current
technology. However, understanding of the chemistry and spectroscopic signatures behind such materials is necessary
for accurate fast fitting algorithms to benefit of the full advantage with advances in hardware. This is especially true as
future users requirements move towards rapid multiplexed analysis and data fusion from a variety of sensors.
The type of explosive materials used in terrorist activities has seen a gradual shift from those that are commonly
manufactured but difficult to obtain, such as trinitrotoluene (TNT) and nitroglycerine (NG), to improvised explosive
devices (IEDs) made from substances that are more readily available. This shift has placed an emphasis on development
of instruments capable of detecting IEDs and their precursors, which are often small, volatile molecules well suited to
detection through mid-infrared absorption spectroscopy. Two such examples are ammonia, a breakdown product of
ammonium nitrate and urea nitrate, and hydrogen peroxide, an efficient oxidiser used in the production of triacetone
triperoxide (TATP) and hexamethyl triperoxide diamine (HMTD). At this meeting in 2007 we presented results of a
hydrogen peroxide detection portal utilising quantum cascade laser (QCL) technology. This trace detection system has
since undergone significant development to improve sensitivity and selectivity, and the results of this will be presented
alongside those of a similar system configured for bulk detection of ammonia. Detection of ammonia produced from the
breakdown of ammonium nitrate has been demonstrated, both on the optical bench and in a walkthrough portal. This
research has been supported by the UK government.
In recent years, quantum cascade lasers (QCL) have been proven in robust, high-performance gas analyzers designed for
continuous emission monitoring (CEM) in harsh environments. In 2006, Cascade Technologies reported progress
towards adapting its patented technology for homeland security applications by publishing initial results on explosive
compound detection. This paper presents the performance and results from a QCL-based people screening portal
developed during the past year and aimed at the detection of precursors used in the make up of improvised explosive
devices (IED). System tests have been carried out on a large number of potential interferents, together with target
precursor materials, reinforcing original assumptions that compound fingerprinting can be effectively demonstrated
using this technique. Results have shown that an extremely high degree of specificity can be achieved with a sub-second
response time. Furthermore, it has been shown that unambiguous precursor signature recognition can be extended to
compound mixtures associated with the intermediate stages in the make up of IEDs, whilst maintaining interferent
immunity. The portal sensitivity was configured for parts per billion (ppb) detection level thresholds, but is currently
being reconfigured for sub-ppb detection. In summary, the results obtained from the QCL based portal indicate that
development of a low cost detection system, with enhanced features such as low false positive and high throughput
screening of individuals or items, is possible. Development and testing was carried out with the support of the UK
government.
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