Standoff detection: classification of biological aerosols using laser induced fluorescence (LIF) technique

Abstract

The release of chemical, biological and explosive (CBE) hazardous materials is a very important and recurring topic concerning personal safety and security. Consistently, the public is shocked by attacks of varying dimensions, which expedites the retrieval of methods to detect and identify hazardous materials at an early stage without having contact to the danger area, inducing the correct counteractions in time to reduce the risk to the public and the emergency services. Especially the detection of biological agents is a major challenge. Laser-based stand-off detection methods, for example LIF, are distance-pillowed, discrete and reliable. The fluorescence signals are distinguishing for the excited molecules and thus allow a relatively accurate classification. Particularly important is the application under real outdoor conditions in order to consider the atmospheric effects, as well as the use of wavelengths in the eye-safe range below 400 nm. Hence, all LIF measurements were studied on a free transmission range at a distance of 20 m from the laser source upon 280 and 355 nm excitation, respectively, to increase the number of discriminating attributes. A number of different chemical and biological substances were tested for their characteristic fluorescence signals and fluorescence lifetimes. The latter are investigated by a gated iCCD camera and analyzed with dedicated software for spectral pattern recognition. The direct comparison of all results leads to a first classification of the various compounds. Finally, the substances are aerosolized to simulate a possible realistic propagation of these materials. The preliminary results confirm classification capabilities of the method.