Dynamics of laser ablation of microparticles prior to nanoparticle generation

To better understand the process of nanoparticle formation when microsphere s are ablated by a high-energy laser pulse, we investigated the Nd:YAG lase r-induced breakdown of 20 mum glass microspheres using time-resolved optica l shadow images and Schlieren images. Time-resolved imaging showed the loca tion of the initial breakdown and the shockwave motion over its first 300 m um of expansion. From these measurements, we determined the shockwave veloc ity dependence on laser fluence. Measured shockwave velocities were in the range of 1-10 km/s. We also developed a numerical model that simulated brea kdown in the glass microsphere and the propagation of this disturbance thro ugh the edge of the sphere where it could launch an air shock. Our objectiv e was to simulate the shockwave velocity dependence on laser fluence and to generate glass density, temperature, and mass velocity profiles after brea kdown. The simulation and experimental data compared favorably. (C) 2001 Am erican Institute of Physics.