Aspects of particulate production from metals exposed to pulsed laser radiation

Experiments have been carried out to investigate particulate production from Al and Cu targets during pulsed laser ablation in vacuum. Ablated material, comprising atomic and particulate fluxes, was deposited onto flat glass and concave mylar substrates. Optical and atomic force microscopy was used to obtain particulate number densities, size and polar distributions as a function of laser focused spot size and power density. Particulate size distributions were fitted to Boltzmann probability distributions, with the increase in energy of the system related to the increase in surface energy during the formation and emission of a spherical particulate from the target surface, qualitatively explaining the observed difference in particulate emission from Al and Cu targets. The laser power density threshold for particulate emission occurred coincident with that calculated for atomic material removal, with a further increase in emission occurring at power densities above 109 W/cm2. Polar particulate emission was fitted to cosθ distributions, indicating that particulates were not emitted in any preferred direction. Particulate production was consistent with a subsurface boiling/cavitation emission process.