Sub-wavelength surface structuring on stainless steel by femtosecond laser pulses

Abstract

In this research, the formation of laser-induced periodic surface structures (LIPSS) on the stainless steel surface by femtosecond laser pulses was investigated under static irradiation and line-scanning experiment. In the experiment, we used a commercial amplified Ti:sapphire laser system that generated 164 fs laser pulses with a maximum pulse energy (Ep) of 1 mJ at a 1 kHz repetition rate and with a central wavelength λ = 780 nm. To obtain a fine periodic ordering of surface nanostructures, the laser beam, through a 0.2 mm pinhole aperture positioned near the 5× objective lens, was focused onto the sample. The samples were mounted on an XYZ-translation stage and irradiated in static and line-scanning experiment. The morphology of the induced periodic structure was examined by scanning electron microscopy. The surface profile was measured by atomic force microscopy. High-spatial-frequency LIPSS (HSFL) with a period of 255 ± 21 nm were obtained over the entire ablated area. HSFL were found to form on low-spatial-frequency LIPSS (LSFL). From our results we elucidated the relationship between the formation of LSFL and HSFL to obtain an enhanced understanding of the mechanism of HSFL formation by femtosecond laser pulses. A large number of applications have been proposed, such as improvement of the optical properties of the surface, new cutting tool development and hard diamond. More applications could be found as the spatial period of HSFL on different materials comes into sub-100 nm.