In this work we examine the feasibility of active thermal sensing of buried objects. A 1.5 kW carbon dioxide laser is used to provide a thermal impulse to the surface of a sand test bed containing simulated metallic landmines. Time- dependent thermal images of the induced surface temperature differentials are obtained using an infrared focal plane array imaging system. Experimental results are reported for two target sizes and four thermal pulse conditions. Quantitative evaluation of the induced surface temperature differentials as a function of time are presented.
Intensity ratios of the resonant Na((lambda) equals 589 nm) to H(alpha ) ((lambda) equals 656 nm) emission lines have been measured for 10 GW/cm2 KrF laser radiation ((lambda) = 248 nm, tpulse equals 17 ns) interacting with 50 micrometers diameter saltwater droplets as a function of position in the breakdown region parallel to the incident laser beam. Results indicate the H(alpha ) emission intensity is highly non-uniform through the plasma plume and is highest in the plume ejected back toward the laser beam. In contrast, the Na emission line intensity shows a much weaker spatial dependence as a function of position within the plasma plume. Calibration data are also reported for the ratio of Na to H(alpha ) emission intensities as a function of Na concentration (0-2000 ppm) for approximately equals 20 micrometers diameter monodisperse droplets located at a fixed observation point in the plasma plume. Future research will extend the ratioing technique to remotely measure droplet salt concentrations in polydisperse saltwater sprays.
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