Generalized Thermo-Elastodynamics for Polycrystalline Metallic Thin Films in Response to Ultrafast Laser Heating

Abstract

A generalized thermo-elastodynamic model applicable to investigating single- and polycrystalline metallic films for their coupled thermal-mechanical responses to ultrafast laser heating is presented. Built upon the two-temperature model, the governing field equations feature hyperbolic electron and lattice energy transports that admit finite propagation speed and incorporate a term of energy dissipation to the generation of thermally induced mechanical disturbance. Electron energy transport in polycrystalline thin film is investigated in-depth by considering temperature dependence and size effect due to film surface and grain boundary scattering. Numerical results generated using the generalized one-dimensional model for a single-crystalline gold film are favorably examined against published experimental data for validation. Several averaged grain diameters are considered to explore the coupled thermal-mechanical responses in polycrystalline gold films of different thicknesses to better understand the dynamics and size effect on energy transport subject to pulsed femtosecond laser.