Ultrafast light coupling with metal surfaces shows strong potential for nanostructuring applications relying on the capacity to localize light energy on the nanoscale. Controlling light confinement requires to understand the transient variation of the optical response during ultrafast irradiation. The fundamental approach we propose based on ab initio calculations allows elucidating the influence of electron-phonon nonequilibrium on optical properties. This results from the investigation of the primary processes responsible for the optical change during laser-solid interaction. Calculations are carried out in the framework of the density functional theory associated to quantum molecular dynamics. Our results shed light on the intricate role of electronic structure modifications and possible optical transitions, driving the laser energy absorption into the material. The revealed key processes based on Fermi smearing on an evolving density of states are of paramount interest for controlling laser energy deposition, surface plasmon excitation and subsequent surface nanostructuring. The calculations predict the possibility of an ultrafast laser-driven plasmonic switch on a typically non-plasmonic material (W), confirmed by pump-probe ellipsometric measurements . The consequence of our results is far reaching as they propose also a route for achieving the highest energy confinement under ultrashort laser irradiation.
 E. Bévillon, J.P. Colombier, V. Recoules, H. Zhang, C. Li, R. Stoian, “Ultrafast switching of surface plasmonic conditions in nonplasmonic metals”, Physical Review B 93 (16), 165416 (2016).
During propagation of high-power femtosecond laser pulse in air dynamic balance between Kerr self-focusing and laser
plasma defocusing results in high localization of the energy in a hundred microns region. Stable long laser filament
forms. For systems of atmospheric optics it is important to control high fluence of the filament. We investigated
numerically the influence of pulse duration and atmospheric aerosol particles scattering on energetic characteristics of
the filamented laser pulse. It was shown that in the conditions of pulse energy remaining the same increase of pulse
duration results in considerable increase of filament length and high-fluence energy transporting by pulse. It is
demonstrated that scattering on atmospheric aerosol particles causes high-fluence energy losses but doesn't prevent
further filament propagation.
The robustness and recoverability of the high-power femtosecond laser pulse filament in the presence of atmospheric
aerosol scattering layer was studied by means of computer simulation. The obtained patterns of fluence and electron
density in a laser filament demonstrate that these parameters acquire a stochastic character inside the aerosol layer and
recover on leaving it. Filament energy decreases with distance inside the layer because of the water particles scattering
and after the layer because of the amplitude-phase perturbations induced by aerosol particles. The equivalence of
nonlinear aerosol medium and linear damping medium with equal to disperse dissipations was investigated.