Development studies reveal that explosives detection is possible behind a barrier placed between a target and a standoff LIBS sensor. Barriers such as polymethylmethacrylate (PMMA) and a variety of glasses have been tested. Results for the detection of organic (DNT, TNT, C4 and H15) and inorganic (sodium chlorate) explosive residues placed up to 30 m from the sensor are presented. The standoff experiments have been evaluated in the emission (studies on laser beam transmission sent by the sensor) and collection (studies on plasma light emission collected by the sensor) channels. These experiments open wide perspectives for the detection of IEDs (improvised explosive devices) through windows located, for instance, inside vehicles, industrial warehouses and buildings where explosive residues have been produced, handled, stored or prepared.
We report on an experimental study of the effect of atmospheric turbulence on laser induced breakdown spectroscopy (LIBS) measurements. The characteristics of the atmosphere dictate specific performance constraints to this technology. Unlike classical laboratory LIBS systems where the distance to the sample is well known and characterized, LIBS systems working at several tens of meters to the target have specific atmospheric propagation conditions that cause the quality of the LIBS signals to be affected to a significant extent. Using a new LIBS based sensor system fitted with a nanosecond laser emitting at 1064 nm, propagation effects at distances of up to 120 m were investigated. The effects observed include wander and scintillation in the outgoing laser beam and in the return atomic emission signal. Plasmas were formed on aluminium targets. Average signal levels and signal fluctuations are measured so the effect of atmospheric turbulence on LIBS measurements is quantified.
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