Early detection and warning of standoff bio-threats using ultraviolet laser wavelengths

The paper presents the results of detection experiments conducted to detect bio-aerosol from a standoff distance of nearly 2 km using laser scattering and ultraviolet laser induced fluorescence (UV-LIF) LiDAR in the presence of potential interfering molecules (molecules having spectrum overlapping with the biological warfare agents). The presence of interfering molecules can make the detection of bio-aerosol difficult. Therefore, conduction of detection experiments in the presence of interfering molecules is a must to develop a system such as to keep the false signal at bay. The software for synchronized spectrum acquisition (gated mode) of UV-LIF signatures of bio-aerosol has been developed and integrated into the system. The detection algorithm on data discrimination has been implemented. Standoff experiments using the developed software have been carried out with the samples consisting of bio-aerosols and interfering molecules. The wavelengths used in the experiments are 266 and 355 nm as the fluorescence quantum yield of two prominent bio-markers is high at these excitation wavelengths. Spectra were acquired with the developed system and analyzed by the developed software. The bio-agents were detected and discriminated from the interfering molecules successfully. In addition to this, the scattering method is also utilized to make distinction between bio and non-bio-molecules using two identical photomultiplier tube detectors based on the depolarization method.