Effects of nanostructure-covered femtosecond laser-induced periodic surface structures on optical absorptance of metals

In this paper, we find, for the first time, that optical absorptance of metals can be significantly enhanced by a new type of surface structures following femtosecond laser ablation, namely nanostructure-covered periodic surface structures. Especially, the effect of the nanostructure-covered periodic structures on optical absorptance of metals has a clear polarization dependence that suggests a more controllable way to modify material optical properties with femtosecond laser processing.