Modeling of Free Electron Laser Ablation

Abstract

Abstract : Development of a coarse-grained chemical reaction model (CGCRM) for incorporation into molecular dynamics (MD) simulations in order to assess the effects of chemical reactions on the ablation process. This model has been successfully applied to the ablation of organic systems and is now being implemented for polymers and biological materials. Development of a combined molecular dynamics and direct simulations Monte Carlo (DSMC) methodology for combining the output from the MD simulations including the presence of clusters into the DSMC calculations that allow for long time and large space development of the plume. Developed a new protocol, substrate-assisted laser-initiated ejection, for mass spectrometry of biological molecules embedded in a water matrix, the simulations were aimed at modeling Charles Lin's (Harvard) drug delivery experiments but have inspired a new set of Mass Spectrometry experiments in Nick Winograd's group (Penn State). Sub-contract to UVa was used to support a graduate (MS) student, Elodie Leveugle. During the reporting period, the focus of the research project of Ms. Leveugle was on the microscopic mechanisms of photomechanical spallation of molecular targets. It has been revealed in a series of large-scale MD simulations that the relaxation of laser-induced thermoelastic stresses is responsible for the nucleation, growth and coalescence of voids in a broad sub-surface region of the irradiated target. Two stages have been identified in the evolution of voids in laser spallation, the initial void nucleation and growth, with the number of voids of all sizes increasing, followed by void coarsening and coalescence, when the number of large void increases at the expense of quickly decreasing population of small voids.