Beam-shape-dependent periodic surface nanostructure using circularly polarized femtosecond laser

In this work, a novel surface periodic nanostructure generation methodology employing shaped circularly polarized femtosecond laser beam was introduced. The orientation of the periodic nanostructure exhibits strong dependence on the beam shape instead of the polarization state of incident laser. In experiments, focused circularly polarized femtosecond laser beams with line-shaped cross section were utilized to normally irradiate the surface of semiconductor or metal, and periodic ripples were generated within the ablation zones. The thresholds for laser pulse energy, pulse number, and beam width of incident laser for ripples generation were investigated. Furthermore, the generation of periodic nanostructures with varying orientations was demonstrated using shaped laser beam with multi- and single-exposure strategies. Our findings suggest a potential means to relax the necessity for high linear polarization in the formation of periodic surface nanostructures.