Femtosecond laser induced micro/nano structures on metals

In this study, novel annular microstructures on metal surfaces were fabricated with a femtosecond laser beam propagating through a microhole and irradiating on the surface of stainless steel SUS 304. The results showed that, with the use of a linearly polarized femtosecond laser beam (800 nm, 120 fs) irradiating through a microhole of diameter 80~100 μm and depth 800 μm, annular microstructures with a period of 4~8 μm were formed. Differing from the laser induced periodic surface structure (LIPSS), the formed annular microstructures are independent of laser polarization. This study speculates that this formation mechanism is due to the interference between the incident laser beam and the reflected beams from the microhole walls.