Reflectivity Change in Nanoscale Modification of DLC Film with Femtosecond Laser Pulses

We have measured the reflectivity of fs-laser irradiated diamond-like carbon (DLC) film, using the pump and probe technique, to understand interaction processes responsible for the bonding structure change and the nanostructure formation that were recently observed in the low-fluence ablation of DLC surface. The results have shown that the characteristic reflectivity change observed as a function of the superimposed laser shots is correlated with the selective change in the bonding structure from sp 3 to sp 2 to induce a swelling of the film surface, and that the nanostructure formation on the DLC surface is certainly preceded by the change in the bonding structure. The experimental results suggest that a local field created with the low fluence fs laser pulse plays an essential role to form the periodic nanostructure on the film surface.