Generation of periodic nanobumps through a double-scan method with femtosecond lasers

Abstract

Ultrafast laser surface structuring is a promising technique for precisely controlling the surface functions of materials. Nanoripples, the typical laser-induced periodic surface structures, are effective at regulating surface colors, but only in one view direction. To overcome this issue, effective methods for fabricating other types of structures are needed. In this study, we successfully form periodic nanobump structures using a simple double-scan approach, in which the same surface is subjected to two consecutive laser scans with different polarization directions. The formation behavior of these intriguing nanostructures is investigated in relation to laser parameters such as peak laser fluence, overlapping ratio, and polarization angle between two scans. The formation mechanism is hypothesized and confirmed. The obtained nanobumps exhibit exceptional optical performance compared to nanoripples by enhancing the visibility angle, hence expanding the possible applications of the ultrafast laser surface structuring technique.