Chemical, biological, radiological, nuclear and explosive (CBRNE) materials can be extremely difficult to detect at a distance using conventional material characterisation techniques, especially in trace amounts. Perhaps of most interest during recent years is the ability to detect residue explosives at a distance, as this could provide a means of detecting improvised explosive devices (IEDs) at a safe distance. LIBS has been shown to be a candidate technology for this, with pioneering developmental work being undertaken by a research group at U.S. Army Research Laboratory (ARL) at Aberdeen Proving Ground, Maryland, U.S.A. Applied Photonics Ltd have supplied a LIBSCAN 100 bench-top system and five experimental prototype Stand-Off LIBS (ST-LIBST) systems to the US Army for use by researchers at ARL (see US Army Research Laboratory). One of these ST-LIBST systems was used during two field trials at National Training Center (California) and another trial at Yuma Proving Ground (Arizona) during the period 2007 - 2008 (see the ST-LIBS™ section of our website).
For CBE threats, LIBS is an excellent tool for tracking the elemental inventory of a given target material, and this ability is boosted by the strong correlation of signal strength with stoichiometry. By use of broadband spectral capture, coupled with advanced chemometrics, a number of laboratories have demonstrated very good performance in True Positives (typically >95% and False Positives <5%). In the case of explosive materials, which as a chemical class exhibit an enhancement of oxygen and nitrogen (NOx-rich) relative to carbon and hydrogen, LIBS can track the increased N/O elemental content very well. Through the use of techniques such as double-pulse LIBS and advanced chemometric analysis of the raw LIBS data, ARL has demonstrated that LIBS is able to discriminate residue explosive from non-explosive materials at stand-off distances in excess of 50 metres. Much work, however, remains to be done to establish the full range of capabilities and limitations. Of particular concern are the safety risks relating to the use of high-power Class IV lasers, although work is ongoing to mitigate these risks through the use of alternative laser wavelengths and other technological means.
For further information on published work in this area, visit our Security Applications Links & Publications page under the Stand-Off LIBS section of our website.
The following spectra were recorded using one of our LIBSCAN 100 modular LIBS systems. The materials analysed are of relevance to CBRNE detection.