Controllable fabrication of metallic micro/nano hybrid structuring surface for antireflection by picosecond laser direct writing

We investigate the effect of micro/nano hybrid structures in cemented tungsten carbide with a focus on optical absorption enhancement. Distinct micro/nano hybrid structures, including regular LIPSS, semi-continuous nano-bumps and nanoscale to microscale protrusions, were induced on WC-Co alloy by picosecond laser irradiation, and reflectance performances of these controllable hybrid structures were compared. We provide insight into mechanisms responsible for protrusion formation by associating hydrodynamic instabilities of molten materials during laser irradiation. Spectral reflectance measurement reveals significant reduction of optical reflectance at laser-treated surfaces in visible wavelength range. The laser induced hybrid structures on WC-Co alloy show potential applications for solar photo-thermal conversion. Investigations of morphology evolution and reflectance performance pave the way for functional surface design via surface structuring process.