Computational model for multiscale simulation of laser ablation
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Computational model for multiscale simulation of laser ablation Leonid V. Zhigilei∗ Department of Materials Science & Engineering, University of Virginia, Charlottesville, Virginia 22904
ABSTRACT Multiscale computational approach that combines different methods to study laser ablation phenomenon is presented. The methods include the molecular dynamics (MD) breathing sphere model for simulation of the initial stage of laser ablation, a combined MD finite element method (FEM) approach for simulation of propagation of the laser-induced pressure waves out from the MD computational cell, and the direct simulation Monte Carlo (DSMC) method for simulation of the ablation plume expansion. The multiscale approach addresses different processes involved in laser ablation with appropriate resolutions and, at the same time, accounts for the interrelations between the processes. A description of the ablation plume appropriate for making a connection between the MD simulation of laser ablation and the DSMC simulation of the ablation plume expansion is discussed. INTRODUCTION The interaction of laser pulses with organic matter leading to the massive material removal (ablation) from a target is a subject of scientific as well as applied interest [1,2]. Important practical applications include laser surgery, matrix-assisted laser desorption/ionization (MALDI) of biomolecules for mass - spectrometric investigations, and surface microfabrication of polymer thin films. During the last several years extensive experimental [1-6], computational [7-16], and theoretical [2,17] efforts have resulted in considerable progress in understanding of many aspects of laser ablation of organic materials. In a big part this progress is due to the development of advanced computational methods and their application to various processes induced by pulsed laser irradiation. In particular, a molecular-level breathing sphere model has yielded a wealth of information on the microscopic mechanisms of laser ablation [7,9,13], parameters of the ejected plume (velocity distributions of matrix and analyte molecules in MALDI [8,10], cluster ejection [11,12,13]) and their dependence on the irradiation conditions (laser fluence [7,9,11], pulse duration [13], initial temperature of the sample [12]). At smaller time- and length-scales, conventional atomic-level MD simulations have demonstrated the ability of this technique to provide detailed information on the dynamics of intermolecular redistribution of the deposited laser energy [14,16] and conformational changes in the molecules undergoing laser desorption [15]. Atomic-level MD simulation technique has been also applied to laser ablation of inorganic materials and first interesting results have been reported [18,19,20]. At the level of the plume expansion, direct simulation Monte Carlo [21-24] and particle-in-cell [25,26,27] methods has been shown to be suitable for realistic simulations of the multi-component ablation plume development on the time- and length-scales of a real experimental configuration. The effec
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