Suppression of ripples on ablated Ni surface via a polarization grating

Gratings were recorded on the surface of nickel by ablation without formation of ripples using an interference of two p-polarized femtosecond laser beams at a π/4 angle of incidence. The mechanism of ripples' suppression is explained by formation of a polarization grating and by ablation at the locations where the polarization is normal to the Ni surface. The aspect ratio of the ablated grooves was ~3 with the period !570 nm at the central wavelength of irradiation of 800 nm. This method is applicable for laser structuring of different materials and a recorded grating structure can be scaled with the irradiation wavelength.