When 3:30 PM - 4:30 PM Mar 17, 2006
Where 1504 Dow Connector
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Molecular Dynamics Modeling of Short-Pulse Laser Ablation: Applications to Laser Shaping of Materials and Puled Laser Deposition

George Gilmer, Lawrence Livermore National Laboratory

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.