Computational Study of the Generation of Crystal Defects and Controlled Modification of Surface Microstructure by Short Pulse Laser Irradiation

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This award supports computational and theoretical research, and education aimed at investigation of a range of fast non-equilibrium processes responsible for material modification and surface nanostructuring by pico- and femtosecond scale laser pulses. The research involves large-scale simulation and has potential for making a transformative impact on the fundamental understanding of material response and microstructure evolution under extreme conditions of ultrafast heating and cooling, as well as for opening new directions for controlled laser material modification with nanoscale resolution. The goal of this research program is to reveal, through large-scale atomistic simulations, the fundamental processes responsible for the modification of surface microstructure of metal targets irradiated by short laser pulses. A computational model combining the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling will be used to perform a detailed analysis of the mechanisms of laser-induced generation of crystal defects and their role in the evolution of surface microstructure and atomic mixing. The conditions leading to the formation of a nanocrystalline surface structure and the atomic-level processes controlling the nucleation and growth of crystallites within a strongly undercooled liquid region of the target will be investigated with a particular focus on the effect of the free surface on the nucleation kinetics and crystallographic orientation of the new grains. The relative contribution of different diffusive and non-diffusive mechanisms of atomic mixing occurring under conditions of rapid melting/solidification, plastic deformation and laser-induced supersaturation with point defects will be investigated in combined molecular dynamics and kinetic Monte Carlo simulations performed for binary alloys and multi-layered targets. The physical processes responsible for the formation/stabilization of metastable crystalline and amorphous phases will be investigated and related to the irradiation conditions in short pulse laser processing. This award supports educational initiatives in the areas of scientific computing and laser-materials interactions include the active involvement of graduate and undergraduate students into various aspects of high-performance computing, development of a new graduate course on Laser-Materials Interactions, as well as incorporation of the research results into an existing course, Introduction to Atomistic Simulations. The PI will continue to maintain close contacts with the Office of Minority Programs in recruiting undergraduate students from traditionally under-represented groups. International collaborations with groups from Germany, France, Russia, and Iraq will involve short and long-term mutual visits and will enrich the educational and cultural experience of the participating graduate and undergraduate students. The educational component of this project also includes a design of an interactive web-site ?Materials under Extreme Conditions.? A non-technical description of general concepts of ultrafast materials phenomena induced by short pulse laser irradiation will be illustrated by the research results obtained in this program and presented in the form of images, computer animations, and simple interactive simulations.