Abstract

We discuss results from molecular dynamics simulations of femtosecond ablation using up to thirty million atoms. These simulations provide a detailed picture of the highly non-equilibrium state of the target material during first few picoseconds after irradiation. Also, information is provided on the ablated material; which may include a liquid film, liquid droplets, and individual atoms. The size and temperature distributions of the ejecta will be discussed. The roles of tensile stress and the nucleation of voids in the removal of material from the target are assessed. The influence of the pulse energy density, initial target temperature, and the equilibration time between the energetic electrons and the ions in the target will be discussed. An important issue for the application to laser shaping of materials is the final surface roughness after material removal. We show that void nucleation is the dominant mechanism causing surface roughening, and we suggest methods to mitigate this problem. The application to pulsed laser deposition is discussed in relation to the ejecta size distribution predicted by the model. We show that the structure of the target can be modified so as to change the size distributions, and improve the uniformity of the films. We discuss Monte Carlo models that can treat the longer time-scales of the impact of the ablation flux on the substrate and the subsequent evolution of the deposit.

 

Biography

Dr. Gilmer is a staff physicist at Lawrence Livermore National Laboratory. Dr. Gilmer holds a B.S. degree from Davidson College in Physics and Mathematics, and a Ph. D. in Physics from the University of Virginia. He then took a postdoctoral position at Cornell, joined the Physics Department at Washington and Lee University for several years, took an Alfred P. Sloan fellowship at Delft Technical University, and then joined the technical staff at Bell Laboratories where he worked for three decades. Over the years his research has been focused on computer simulations of materials processing at the atomistic level, including crystal growth, thin film deposition, ion implantation and laser excitations. At Livermore he is working in several areas related to the National Ignition Facility for inertial confinement fusion and in silicon device processing. He has strong personal connections to Virginia Tech, including a brother Thomas who served on the Physics faculty in several positions for a number of years, and a son Hendrik who recently graduated with a Bachelors degree in Electrical Engineering – and who found a job that utilized his training!