Ultrafast laser-induced periodic-surface structure: Formation mechanisms and plasmonic effects

Abstract : Ultrafast laser radiation has a strong potential for surface structuring on ultimate scales due to a strongly localized character of energy deposition. Depending on laser parameters and material properties, these self-formed structures develop with varying periodicity and amplitudes. We propose here a study concerning the effect of energy coupling on laserinduced periodic surface structure (LIPSS) formation. We generated LIPSS on various materials with different electronic configuration in order to investigate the influence of the electron-phonon coupling strength and thermal diffusion efficiency on the specific contrast of LIPSS. Representative metals (simple, transition, noble) with a large range of coupling strengths were exposed to ultrafast laser excitation and the patterning surface was investigated ex-situ by atomic force microscopy, and scanning electron microscopy. The relative strength and the electron temperature dependence of the electron-phonon coupling in the metals are identified as key factors affecting the initial energy redistribution and the dimensional size of the region undergoing transient melting and resolidification. It appears that growth of the contrast and increase of the ripples height are correlated to the evolution of the constant of coupling and to the amount of material experiencing solid-to-liquid transitions. Plasmonic effects are also investigated as a key parameter for ultrafast laser energy coupling and explanation of ripples orientation with laser polarization.