Switchable formation of diverse regular nanostructures on metal by dual correlated femtosecond laser irradiations

Manipulation of material properties via femtosecond laser-induced periodic surface structures is of significant importance for many practical applications in optics, tribology and wettability, but it is still a substantial challenge for single-beam femtosecond laser irradiation. We here report a strategy to uniformly generate largearea periodic nanostructures on molybdenum surface by utilizing cylindrical focusing of double time-delayed femtosecond blue lasers with orthogonal linear polarizations. It is found that three different types of periodic surface structures can be controlled and actively transformed through properly adjusting the energy fluence ratios between double laser pulses. The remarkable long-range uniform property is clearly identified by both the microscopic observation and Fourier frequency analysis. The obtained minimum structural size and period approximate 140 nm and 260 nm, respectively. The underlying mechanisms are attributed to the complex surface plasmon excitation during the temporally correlated dynamic process of dual laser-material interactions. These investigations help to facilitate femtosecond laser nanostructuring into a robust and versatile way.

Automated summary

Manipulation of material properties through femtosecond laser-induced periodic surface structures is a major challenge for single-beam femtosecond laser irradiation. In this study, we developed a strategy to uniformly generate large-area periodic nanostructures on molybdenum surface using double time-delayed femtosecond blue lasers with orthogonal linear polarizations. Through adjusting the energy fluence ratios between the two laser pulses, three different types of periodic surface structures can be controlled. The obtained structural sizes and periods are approximately 140 nm and 260 nm, respectively. This research contributes to the advancement of femtosecond laser nanostructuring.