Polarization-independent surface nanostructuring by femtosecond laser irradiation via microsphere in far field and ambient air

Abstract Ultrafast lasers have garnered significant interest in the realm of surface nanofabrication. However, their dynamic electric field distribution is influenced by the polarization direction when pursuing high machining precision, which leads to high polarization dependence of laser nanostructuring. Here, polarization-independent surface nanostructuring is realized on Sb 2 S 3 thin films by femtosecond laser irradiation via a microsphere in the far field and ambient air. The formation of nanogrooves is ascribed to surface thermal stress during melting, re-solidification, and super-cooling under high-repetition-rate femtosecond laser irradiation. The influence of materials melting and ablation on the electric field distribution during the laser processing is analyzed. In the molten state, the distribution of the electric field remains unaffected by polarization, enabling the realization of polarization-independent nanoprocessing based on the thermal stress induced by a temperature gradient. The feature sizes of surface nanostructures can be precisely adjusted by varying laser fluence, and the minimum size down to approximately 38 nm (λ/27) is achieved. This innovative laser nanostructuring technique, operating in the far field and ambient air, holds considerable promise for advancing next-generation nanofabrication.