Numerical simulation of ballistic electron dynamics and heat transport in metallic targets exposed to ultrashort laser pulse

Abstract

The role of ballistic electrons generated during ultrashort pulse laser (USPL) absorption in metallic targets was investigated in a wide range of laser intensities using our developed simulation package FEMTO-2D. The simulation package is based on the numerical solution of the two-temperature model with the assumption of local thermal equilibrium for electron and lattice subsystems within the simulation cell at any time step. Electron thermodynamic parameters were calculated through the processes of material transition from the cold solid state into the dense plasma state during and after the pulse based on the collision theory. The appropriate model for temperature dependent thermodynamic parameters allows defining the heat transport during an early stage of the USPL-matter interaction directly, without relying on the effective absorption depth model. The study investigated, for the first time, using integrated computer simulation the role of ballistic electrons in energy transfer and heat conduction during USPL deposition. The simulation predictions of the electron heat transport dynamics during and shortly after the laser pulse were benchmarked for the gold target against available experimental data and were able to confirm the dominant role of the ballistic electrons in the initial heat propagation within 100–120 nm of the target at laser intensities below 1013 W/cm2.