Atomic/Molecular-Level Simulations of Laser–Materials Interactions

Abstract

Summary. Molecular/atomic-level computer modeling of laser-materials interactions is playing an increasingly important role in the investigation of complex and highly nonequilibrium processes involved in short-pulse laser processing and surface modification. This chapter provides an overview of recent progress in the development of computational methods for simulation of laser interactions with organic materials and metals. The capabilities, advantages, and limitations of the molecular dynamics simulation technique are discussed and illustrated by representative examples. The results obtained in the investigations of the laser-induced generation and accumulation of crystal defects, mechanisms of laser melting, photomechanical effects and spallation, as well as phase explosion and massive material removal from the target (ablation) are outlined and related to the irradiation conditions and properties of the target material. The implications of the computational predictions for practical applications, as well as for the theoretical description of the laser-induced processes are discussed. IntroductionShort-pulse lasers are used in a diverse range of applications, from advanced materials processing, cutting, drilling, and surface micro-and nanostructuring [1,2] to pulsed-laser deposition of thin films and coatings [3], laser surgery [4,5], and artwork restoration [6,7], and to the exploration of the conditions for inertial confinement fusion, with the world's most energetic laser system being built at the National Ignition Facility at Lawrence Livermore National Laboratory [8]. At the fundamental science level, short-pulse laser irradiation has the ability to bring material into a highly nonequilibrium state and provides a unique opportunity to probe the material behavior under extreme conditions. In particular, optical pump-probe experiments have been used to investigate transient changes in the electronic structure of the irradiated surface with high (often subpicosecond) temporal resolution [9][10][11][12][13], whereas recent advances in time-resolved X-ray and electron diffraction

Atomistic Simulation Study of Short Pulse Laser-Induced Generation of Crystal Defects in Metal Targets

“…Before discussing the effect of the spatial confinement on the material response to the laser excitation, we would like to distinguish it from the thermal and stress confinement realized when the characteristic times of the redistribution of the absorbed laser energy by thermal conduction or stress waves are longer than the time of the temperature increase due to the laser energy deposition [113,120,121,152,167,238]. The condition for the thermal confinement, in particular, can be expressed as ) 2 /( } , max{ , Ref.…”

“…In the absence of the overlayer, the expansion of the surface region results in the tensile stresses and, concurrently, a transient temperature drop that can be estimated by considering the expansion as an isentropic process, for which   [118,121] where cp is the specific heat capacity per unit volume and  is the volume coefficient of thermal expansion. At the same time, the equilibrium melting temperature is also affected by the negative stresses, with the variation of the melting temperature described by the Clapeyron…”

“…Together, the advantages of the two methods can be combined to overcome the individual limitations of TTM and MD method. Accordingly, a hybrid atomistic-continuum (TTM-MD) model has been developed in order to accurately describe the diverse range of processes induced by short pulse laser irradiation of a metal target [115][116][117][118][119][120][121].…”

“…Indeed, the emission of partial dislocations from the melting front [121,177], plastic deformation of films heated by a laser pulse [178], generation of nanocrystalline structure [179] and dislocations [180,181] around the regions of localized laser energy deposition, strong supersaturation of a surface layer with vacancies [129], and transformation of a lattice-mismatched interface into a threedimensional periodic array of stacking fault pyramids outlined by stair-rod partial dislocations [141] have been observed in MD simulations.…”

“…Molecular dynamics (MD) simulations are playing an increasingly important role in investigations of the complex and highly non-equilibrium processes induced by short pulse laser irradiation, see reviews [121,160]. In particular, MD simulations of laser interactions with metal targets have provided important insights into the mechanisms and atomic-level dynamics of laser melting [118,120,129,141,143,161,162].spallation [117,118,120,152,153] and explosive boiling [120,146].…”