Reflectivity in femtosecond-laser-induced structural changes of diamond-like carbon film

We report characteristic changes in reflectivity of diamond-like-carbon (DLC) films following irradiation of femtosecond laser pulses at laser fluence around the ablation threshold, where we have observed the formation of periodic nanostructure on the film surface and the modification of bonding structure from DLC to glassy carbon in our recent experiments. The experimental results have shown that the reflectivity change should be a reliable measure to monitor the experimental condition to produce the structural changes, being closely associated with the fundamental physical process to induce these phenomena. PACS 79.20.Ds; 81.40.Tv; 42.62.Cf