Abstract
Summary form only given. We study a new method for producing ultrafine particles (nanoparticles) that employs pulsed-laser ablation of microparticles. Pulsed Nd:YAG laser radiation, 10-ns pulses at 1064 nm, was used to ablate 20-/spl mu/m glass microspheres; and pulsed excimer laser radiation, 15-ns pulses at 248 nm, was used to ablate /spl sim/-2-/spl mu/m feedstock of silver, gold, and Permalloy under both normal atmospheric conditions and other ambients. Pump-probe imaging verified that breakdown in the dielectric particles initiated near the back surface due to internal focusing and became the source for shock wave formation. After plasma breakdown and shock wave propagation through the initial particle, a large fraction of the original mass was converted to nanoparticles. In order to better understand this process, we have illuminated exploding glass particles with time-delayed second-harmonic laser pulses to image both the ejected material (shadow image) and the propagating shock wave (Schlieren image).
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