Rotationally symmetric colorization of metal surfaces through omnidirectional femtosecond laser-induced periodic surface structures.

Following femtosecond (fs) laser pulse irradiation, the formation of a new type of low-spatial-frequency laser-induced periodic surface structure (LSFL) patterns, namely, omnidirectional LSFLs (OD-LSFLs) with the periodic ordering of their orientations, are investigated on Ni in this Letter. Using a liquid crystal polymer patterned depolarizer, we periodically rotate the polarization of fs laser pulses across the laser spot and create OD-LSFLs by raster scanning fs laser pulses. We also show that the period of the OD-LSFL orientation rotation can be controlled with the defocused distance, and OD-LSFLs can significantly expand the viewing angle of the structural colors in the azimuthal direction without noticeable color degradations.