Periodic nanostructure formed on TiN and DLC by femtosecond laser pulses

Hard coatings of TiN and DLC were irradiated by 800- and 267-nm, femtosecond (fs) laser pulses at an energy fluence slightly above the ablation threshold. On the ablated thin-film surfaces, the linearly-polarized fs pulses produce arrays of fine periodic structures that are almost oriented to the direction perpendicular to the laser polarization, while the circularly-polarized light forms fine dot structures. The size of these surface structures is 1/10-1/5 of the laser wavelength and decreases with a decrease in the laser wavelength.