Plasmonic and Hydrodynamic Effects in Ultrafast Laser-Induced Periodic Surface Structures on Metals

We report results on the development of laser-induced periodic surface structures produced by ultrashort laser pulses irradiating metallic surfaces. The surface topology features are discussed in terms of periodicity and amplitude contrast of the pattern formation, and in relation to the chronological sequence of laser-induced events. Resonant excitation of Surface Plasmons in metallic gratings show that the surface wave excited during the femtosecond laser pulse can initiate the observed patterning. Metallic behavior under nonequilibrium conditions on the picosecond timescale is then investigated to correlate the amount of material experiencing solid-to-liquid transitions and the subsequent structure amplitude. With the derived observation, the calculation of the transient nonequilibrium thermodynamic characteristics of excited nickel is performed, allowing to define characteristic timescales of thermocapillary processes which may occur under multi-pulse irradiation.