Microsphere femtosecond laser sub-50 nm structuring in far field via non-linear absorption

Abstract

Creation of arbitrary features with high resolution is critically important in the fabrication of nano-optoelectronic devices. Here, sub-50 nm surface structuring is achieved directly on Sb₂S₃ thin films via microsphere femtosecond laser irradiation in far field. By varying laser fluence and scanning speed, nano-feature sizes can be flexibly tuned. Such small patterns are attributed to the co-effect of microsphere focusing, two-photons absorption, top threshold effect, and high-repetition-rate femtosecond laser-induced incubation effect. The minimum feature size can be reduced down to ~30 nm (<italic>λ</italic>/26) by manipulating film thickness. The fitting analysis between the ablation width and depth predicts that the feature size can be down to ~15 nm at the film thickness of ~10 nm. A nano-grating is fabricated, which demonstrates desirable beam diffraction performance. This nano-scale resolution would be highly attractive for next-generation laser nano-lithography in far field and in ambient air.