Femtosecond-Laser-Induced Nanostructures Formed on Hard Coatings of TiN and DLC

摘要

Linearly- and circularly-polarized femtosecond (fs) Ti:sapphire laser pulses at 800 and 267 nm were focused in air to ablate hard thin films of TiN and DLC deposited on stainless steel plates. The morphology of the thin film surfaces that were ablated by the fs laser pulses at an energy fluence slightly above the ablation threshold was observed and characterized with a field emission-scanning electron microscope. With the linearly-polarized light, arrays of fine slender granular structure were produced on the ablated surface, which were almost oriented to the direction perpendicular to the laser polarization. On the other hand, the circularly-polarized light is found to form fine dot structures on the film surface. The size of these surface structures was 1/10～1/5 of the laser wavelength used and was observed to decrease with a decrease in the laser wavelength. It should be noted that the size of surface structures observed is much smaller than that of the well-known surface ripple patterns produced by the laser-induced surface electromagnetic wave.