Sub-100-nm periodic nanostructure formation induced by short-range surface plasmon polaritons excited with few-cycle laser pulses

We have demonstrated that intense 7-fs, similar to 810-nm laser pulses can produce a much finer periodic nanostructure on a diamond-like carbon film through ablation in air than that formed with intense 100-fs, similar to 800-nm laser pulses. The minimum period size is similar to 60nm, corresponding to similar to 1/13 of the center wavelength. To understand the physical mechanism responsible for the finer nanostructuring, we have observed a bonding structural change in the nanostructure with micro-Raman spectroscopy and a scanning transmission electron microscope. It has been found that the modified layer thickness with the 7-fs pulses is much thinner than that with the 100-fs pulses. The results show that the 7-fs pulses create a few-nm-thick layer with high-density electrons and excite short-range surface plasmon polaritons, which have a large wave number around the layer and induce the plasmonic near-field nanoablation. The period size estimated by using a model target reproduces well the observed size of nanostructures.