Fourier Transform infrared spectroscopy (FTIR) is regularly used in forensic analysis, however the application of high resolution Fourier Transform infrared spectroscopy for the detection of explosive materials and explosive precursors has not been fully explored. This project aimed to develop systematically a protocol for the analysis of explosives and precursors using Fourier Transform infrared spectroscopy and basic data analysis to enable the further development of a quantum cascade laser (QCL) based airport detection system. This paper details the development of the protocol and results of the initial analysis of compounds of interest.
Advances in the application of Quantum Cascade Lasers (QCL) to trace gas detection will be presented. The
solution is real time (~1 μsec per scan), is insensitive to turbulence and vibration, and performs multiple
measurements in one sweep. The QCL provides a large dynamic range, which is a linear response from ppt to
% level. The concentration can be derived with excellent immunity from cross interference. Point sensing
sensors developed by Cascade for home made and commercial explosives operate by monitoring key
constituents in real time and matching this to a spatial event (i.e. sniffer device placed close to an object or
person walking through portal (overt or covert). Programmable signature detection capability allows for
detection of multiple chemical compounds along the most likely array of explosive chemical formulation.
The advantages of configuration as "point sensing" or "stand off" will be discussed. In addition to explosives
this method is highly applicable to the detection of mobile drugs labs through volatile chemical release.
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.
Following the development of point sensing improvised explosive device (IED) technology[1] Cascade Technologies have
initial work in the development of equivalent stand-off capability. Stand-off detection of IEDs is a very important technical
requirement that would enable the safe identification and quantification of hazardous materials prior to a terrorist attack. This
could provide advanced warning of potential danger allowing evacuation and mitigation measures to be implemented.
With support from the UK government, Cascade Technologies is currently investigating technology developments aimed at
addressing the above stand-off IED detection capability gap. To demonstrate and validate the concept, a novel stand-off
platform will target the detection and identification of common high vapor pressure IED precursor compounds, such as
hydrogen peroxide (H2O2), emanating from a point source. By actively probing a scene with polarized light, the novel
platform will offer both enhanced selectivity and sensitivity as compared to traditional hyperspectral sensors, etc. The
presentation will highlight the concept of this novel detection technique as well as illustrating preliminary results.
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.
Following Cascade Technologies first success at using Quantum Cascade Lasers (QCL) for trace gas detection in the continuous emission monitoring market, the core technology platform is now being developed towards homeland security applications.
This paper will highlight the potential of QCL based trace gas sensor for detecting vapours of explosives. Furthermore we will present results that let foresee the use of such technologies at addressing security gaps for protection against terrorism in infrastructures where high throughput screening of individuals or items is required. Preliminary measurements have shown that rapid identification, or fingerprinting, of explosive is achievable in 10ms at extrapolated sensitivities in the sub-part per billion range.
The experiments were carried out with support form the Home Office Scientific Development Branch (HOSDB) in the UK and were focused at selecting a variety of explosive compounds and showing their detection using a novel sniffer platform system based on the use of quantum cascade lasers. Preliminary studies on the technology have indicated that direct fingerprinting (detection - identification) of explosive compounds such as NG and tagging agents such as EGDN by sniffing surrounding ambient air is achievable. Furthermore these studies have also indicated that detection of such compounds on packaging used to ship the sealed compounds is possible, making this platform a strong contender for detection through cross contamination on material that have been in contact with each other. Additionally, it was also possible to detect breakdown products associated with sample material NG providing a further capability that could be exploited to enhance the detection and identification of explosive compounds.
We show that by using a high resolution Fourier transform infrared spectrometer we can map the temporal characteristics of a pulsed quantum cascade laser into the wavenumber domain, and hence show that when a square current pulse is applied to a distributed feedback laser a linear sub-microsecond frequency chirp is developed. We describe a mid infrared spectrometer, that is based upon the use of this linear chirp, which can provide a real-time display of the spectral fingerprint of molecular gases. The sensitivity of the spectrometer is based upon the use of long pathlength White or Herriot cells, and the multiplex advantage associated with recording the entire spectral window during each electrical pulse. For a cell with a path length of 9.6 m, dilution measurements made on the ν9 band transistions of 1,1 difluoroethylene indicate a sensitivity of 30 parts per billion.
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