Azimuthal angle- and scanning pitch-dependent colorization of metals by ultrashort laser pulses

Abstract

We report the modification of optical properties of 304 stainless steel surfaces by femtosecond laser direct writing with different scanning pitches. Regularly arranged ripples with a spatial period of ~700 nm were obtained, rendering vivid structural colors when we illuminated the surface with white light. Diffraction spectra were generated to investigate the spectral properties of the structural colors. Results indicate that the diffraction maximum strongly depends on scanning pitch and azimuthal angle, but that the central wavelength is insensitive to both of them. The reflectance properties were also investigated. This study adds a new parameter, the scanning pitch, to the list of parameters in the production of controllable colorized metal, which may find a range of applications in color display, decoration, and so on.