Nanostructuring of silicon surface with near-field enhanced in femtosecond laser ablation

Intense ultrashort laser pulses are able to produce periodic nanostructures through ultrafast ablation of solid surfaces, where the observed size of nanostructures is much smaller than the laser wavelength [1,2]. Intensive studies have been made for a variety of target materials to elucidate the nanostructuring. However, the physical process is not completely understood yet. Based on a series of experimental studies for hard thin films such diamond-like carbon and TiN [2,3], we have shown that near-field enhanced with femtosecond (fs) laser pulses plays the essential role in initiating the nanoscale ablation on the target surface [4], and the origin of nano-periodicity observed can be attributed to the excitation of surface plasmon polaritons (SPPs) in the surface layer [5] where the dielectric properties are rapidly changed due to the generation of high-density free electrons.