Herein, a poly(vinylpyrrolidone) (PVP)-free method is described for synthesizing Ag nanoplates that have localized surface plasmon resonance in the near-infrared (NIR) range. Citrate-capped Ag spherical nanoparticles are first grown into small Ag nanoplates that resonate in the range of 500-800 nm. The small Ag nanoplates are used as seeds to further grow into large Ag nanoplates with a lateral dimension of 100-600 nm and a plasmon resonance wavelength of 800-1660 nm and above. The number of growth steps can be increased as desired. Without introducing additional citrate into the solutions of small Ag nanoplate seeds, large Ag nanoplates can be synthesized within minutes. The entire synthesis is completely PVP free, which promotes the nanoparticle growth along the lateral direction to form large Ag nanoplates. The multistep growth and the minimum usage of citrate are essential for the fast growth of high-aspect-ratio Ag nanoplates resonating in the NIR range.
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 ofthe 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.
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