Ultrafast thermalization dynamics in Au/Ni film excited by femtosecond laser double-pulse vortex beam

Abstract

We theoretically investigated ultrafast thermalization dynamics of spatio-temporal evolutions of temperature fields in typical Au/Ni film excited by femtosecond laser double-pulse vortex beam. It is proposed that the enhanced energy deposition in the layered Au/Ni film can be unprecedentedly facilitated via applying femtosecond laser double-pulse vortex beam, preferentially giving rise to vortical thermalization for the phonon system of bottom Ni layer on picosecond timescale. It can be explained as the intensified dynamics of double-pulse vortex beam interacting with the excited intermediate state of Au/Ni film and the following energy competitive processes of the electron thermal diffusion and the electron-phonon coupling in respective layers. Moreover, the electron-phonon coupling period of Au/Ni film with respect to the crucial laser parameters of pulse separation and vortex beam fluence are explored in details. The results can be basically helpful for understanding the ultrafast dynamics of vortical thermalization for advancing the potential applications of compound-cavity fabrication, stimulated emission depletion (STED) imaging and ultrahigh time-resolved spectroscopy, etc.