Laser Writing of Multilayer Structural Colors for Full‐Color Marking on Steel.

Laser‐induced periodic surface structure (LIPSS) can form structural color on the metal surfaces with high production efficiency and thermal stability, and has been used in various industrial applications such as unfaded color marking and anti‐counterfeiting. Herein, a novel fabrication scheme of multilayer LIPSS is proposed by multiple writing in situ with changing the laser polarization direction, to exhibit an effect of color superposition. To verify this approach, the color formation mechanism of LIPSS on the stainless‐steel surface is analyzed by finite‐element numerical calculation and reveals that the high‐angular dispersion of LIPSS is mainly the result of optical diffraction occurring on the surface of periodic structures. The relationship between the angular dispersion of multilayer LIPSS and laser‐processing parameters is established. Through the proposed multilayer LIPSS coloring technology, vivid full‐color patterns on the steel surface are demonstrated, and the in situ superposition of three‐layer graphs is realized, which can greatly enrich the color levels and be competitive in industrial applications. [ABSTRACT FROM AUTHOR]