Dynamics of laser ablation of microparticles prior to nanoparticle generation

Abstract

To better understand the process of nanoparticle formation when microspheres are ablated by a high-energy laser pulse, we investigated the Nd:YAG laser-induced breakdown of 20 μm glass microspheres using time-resolved optical shadow images and Schlieren images. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 300 μm of expansion. From these measurements, we determined the shockwave velocity dependence on laser fluence. Measured shockwave velocities were in the range of 1–10 km/s. We also developed a numerical model that simulated breakdown in the glass microsphere and the propagation of this disturbance through the edge of the sphere where it could launch an air shock. Our objective was to simulate the shockwave velocity dependence on laser fluence and to generate glass density, temperature, and mass velocity profiles after breakdown. The simulation and experimental data compared favorably.