The most desirable configuration for detection of toxic chemicals utilises the maximum distance between detector and
hazard. This approach minimises the contamination of equipment or personnel. Where the target chemical is an involatile liquid, indirect detection of the liquid contamination is made difficult by inherently low vapour pressure. In this instance, direct detection of the chemical hazard is the best approach. Recent technology developments have allowed spectroscopic systems to provide multiple options for the stand-off detection of involatile chemical warfare agents (CWAs). Two different stand-off spectroscopic systems, based upon IR absorption and Raman spectroscopic techniques are described here. The Negative Contrast Imager (NCI) is based upon an optical parametric oscillator (OPO) source comprising a Q-switched intracavity MgO:PPLN crystal. This crystal has a fanned grating design and wavelength tuning is achieved by translating the PPLN crystal within the 1064 nm pump beam. This approach enables the production of shortwave and midwave IR radiation (1.5 – 1.8 μm and 2.6 – 3.8 μm, respectively), which is scanned across the scene of interest. Target materials that have an absorption feature commensurate with the wavelength of incoming radiation reduce the intensity of returned signal, resulting in dark pixels in the acquired image. This method enables location and classification of the target material. Stand-off Raman spectroscopy allows target chemicals to be identified at range through comparison of the acquired signature relative to a spectral database. In this work, we used a Raman system based upon a 1047 nm Nd:YLF laser source and a proprietary InGaAsP camera system. Utilisation of a longer excitation wavelength than most conventional stand-off detection systems (e.g. 532 or 785 nm) enables reduction of fluorescence from both the surface and the deposited chemicals, thereby revealing the Raman spectrum. NCI and Raman spectroscopy are able to detect CWAs on surfaces at distances of 2 – 10 metres and have potential to detect over longer ranges. We report the successful identification of at least 60 μl of nitrogen mustard at a distance of a 2 m and 10 m using NCI and Raman spectroscopy.
In the past few years, there has arisen an intense demand for new generation technologies which provide for the rapid
and sensitive stand-off detection of explosive compounds and hazardous chemicals. This has been fueled, in large part,
by the escalation of threats to homeland security and the debilitating effects of IED devices in both civilian and war
zones. In this paper, we describe two portable stand-off Raman spectrometers which have been developed by DeltaNu
and are intended for use in different test environments. The first, the DeltaNu ObserveR™, is a handheld785 nm laser
device suited for the close range detection of explosive materials during nighttime operations, or indoors under restricted
light conditions. The second device, the ObserveR LR, is a tripod-mounted, solar blind system that enables detection at
longer distances (ca. <30 m) with reduced fluorescence interference. A condensed summary is presented of different
tests that have been conducted using these devices, and results are discussed within the context of technological
improvements that will be required to adequately meet the challenge of robust explosive material detection.