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

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 femto-second 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 un-derstanding the ultrafast dynamics of vortical thermalization for advancing the potential applications of compound-cavity fabrication, stimulated emission depletion (STED) imaging and ultrahigh time-resolved spec-troscopy, etc.