Improving Raman stand-off distance for the detection of chemical warfare agents

Operating a chemical detector system at a stand-off distance from a hazard is advantageous. By increasing the distance between the detector and the hazard, the risk of contamination decreases, whilst increasing personnel safety. The aim of this work is to develop an optical bench mounted system for presumptive identification of toxic chemical simulants at a stand-off distance. Unlike commercially available instruments, the Dstl system is not a light tight unit, but instead offers a platform in which different optical sub-components can be tested in an attempt to optimise the overall sensitivity of the system. By operating in a pulsed mode, not only is detector noise reduced but also the background radiation due to laboratory light. To test its performance, the Dstl Raman system was assessed at a stand-off distance of 2 m and collected spectra from Raman standard materials. Additional work was conducted with the Dstl Raman system to collect spectra from toxic chemicals associated with chemical warfare agents (CWAs). Indicative comparisons were made against data collected on commercially available systems, in order to identify future development for the Dstl system. Overall, this research piece aimed to exploit the powerful discriminatory nature of the Raman technique whilst demonstrating it under room lights and at useful stand-off distances. The Dstl stand-off Raman system performed well and provided clean spectra for the CWA simulant study. However all the tests reported here were measured on bulk samples and further work is needed to determine how the system performs against samples deposited as thin layers on realistic substrates