Computer modeling of laser interactions with materials

Short-pulse laser irradiation can induce a range of fast non-equilibrium processes in an irradiated target, from strong overheating and fast melting to an explosive boiling and massive material removal (ablation). Practical applications of pulsed laser irradiation range from surface micro/nano-processing and pulsed laser deposition of thin films and coatings to laser surgery and mass spectrometry of biomolecules. We are performing computational investigation of laser-materials interactions aimed at obtaining a fundamental understanding of the fast non-equilibrium processes induced by short pulse laser irradiation, as well as on the analysis of practical implications of the revealed physical picture for the advancement of laser technologies.

Laser interactions with metals

Computer modeling of laser interactions with metals is a new active direction in our group. Currently two graduate students, Dmitri Ivanov and Bill Duff are working on this project. We are developing a hybrid model that combines classical molecular dynamics (MD) method for simulation of non-equilibrium processes of lattice superheating and fast phase transformations with a continuum description of the laser excitation and subsequent relaxation of the conduction band electrons based on the two-temperature model (TTM). In the hybrid TTM-MD method, MD substitutes the TTM equation for the lattice temperature and the diffusion equation for the electron temperature is solved simultaneously with MD integration of the equations of motion of atoms [PRB03]. First applications of the TTM-MD model have provided insights into the microscopic mechanisms of laser melting and disintegration of Ni and Au films [PRL03, PRB03, APA04b, ASS05], photomechanical spallation of bulk Ni targets [APA04a, HPLA04], as well as disintegration and ablation of Cu targets [PRB02]. The hybrid model was also used in a recent study of shock-induced heating and melting of a grain boundary region in an Al crystal [SHOCK03]. Recent progress in the model development and new results on laser interaction with metal targets are described on our web page on laser - metal interactions.

Laser interactions with organic targets

We are developing a coarse-grained mesoscopic model for simulation of laser ablation of organic targets. The initial work performed at Penn State (Group of Barbara J. Garrison) and University of Virginia was focused on laser ablation/desorption of simple molecular systems with application in matrix-assisted laser desorption/ionization (MALDI) of biomolecules. This work has provided detailed information on the microscopic mechanisms of laser ablation [CPL97, JAP00], parameters of the ejected plume (velocity distributions of matrix and analyte molecules in MALDI [APL97, RCMS98], cluster ejection [APL99, APA03]) and their dependence on the irradiation conditions (laser fluence, pulse duration, initial temperature of the sample [APA99]). The results obtained for molecular systems and MALDI are reviewed in two recent review papers [CR03, IJMS03] and described on our web page on ablation of molecular substrates.
Recent studies included a detailed analysis of the mechanisms of cluster formation in laser ablation [APA03] and investigation of the evolution of voids in photomechanical front-surface laser spallation of the irradiated target [APA04a, APA04c].
Subsequent work is focused on the extension of the computational model to more complex composite organic targets, such as soft biological tissue (Elodie Leveugle), as well as on investigation of the ionization mechanisms in MALDI (collaboration with Richard Knochenmuss).

Publications: you can find a complete list of our papers on laser interactions with materials by following this link.

Animations from simulations of laser melting, spallation, and ablation: you can view animated sequences of snapshots from the simulations of laser melting, spallation, and ablation by clicking on images below.

Animated sequences of snapshots from MD simulations of photomechanical damage/spallation of a molecular target

Animated sequences of snapshots from TTM-MD simulations of laser melting

Animated sequences of snapshots from coarse-grained MD simulations of laser ablation