Metal surface coloration by oxide periodic structures formed with nanosecond laser pulses

- Steel surface coloration was made by small-scale spatially periodic structures.
- AFM, SEM and Raman scattering measurements of obtained structures were done.
- The surface color depends on the period, height and orientation of structures.
- Structures orientation is a function of laser polarization or incident angle.
- Formed markings change their color under the different viewing angles.

In this work, we studied a method of laser-induced coloration of metals, where small-scale spatially periodic structures play a key role in the process of color formation. The formation of such structures on a surface of AISI 304 stainless steel was demonstrated for the 1.06 µm fiber laser with nanosecond duration of pulses and random (elliptical) polarization. The color of the surface depends on the period, height and orientation of periodic surface structures. Adjustment of the polarization of the laser radiation or change of laser incidence angle can be used to control the orientation of the structures. The formation of markings that change their color under the different viewing angles becomes possible. The potential application of the method is metal product protection against falsification.