High-efficiency-and-quality nanostructuring of molybdenum surfaces by orthogonally polarized blue femtosecond lasers

Abstract

Femtosecond laser-induced periodic surface structures featured by a mask-free and one-step procedure provide a new fascinating prospect for the high precision manufacture applicable to diverse materials, but still face challenges in both the fabrication efficiency and the structure quality. Here, a homogenous large-area nanolithography is implemented on molybdenum surface, through using cylindrical focusing of double temporally delayed blue femtosecond lasers with orthogonal polarizations. The achieved grating structures present some unique features including the ablated narrow groove width of 100 nm, the small period of 245 nm, the smooth ridge profiles, and especially the uniform distribution in a mm-scaled range without bending, spitting and interruption. The calculated structure orientation angle shows an unprecedentedly minimum dispersion value of 5°, indicting a significant improvement on the structure uniformity compared with the observations of the single-beam femtosecond laser irradiation. The simulation results reveal that the transient spatiotemporal correlations between the localized electromagnetic field distributions from the double orthogonally polarized laser pulses constitutes a positive feedback mechanism to regularize the growth of the surface structures. A macro-sized surface pattern of such uniform structures displays good monochromatic colors and excellent broadband antireflection performances. This efficient laser nanolithography facilitates the applications in the fields of nanooptics.