Sequential colorization of steel surface by ps laser texturing

To render metal surfaces to various desirable colors without changing their chemical composition is necessary and important in many applications including decoration, marking, data storage, and anti counterfeiting. In this paper, we report a surface micro/nano texturing technique by utilizing a high power (with an average power up to 100 W) and high repetition rate (with a maximum of 2 MHz) picosecond laser beam to colorize metal surfaces. Sequential colors varying from golden to deep plum were realized on steel surfaces by simply changing the ps laser scanning speeds. Systematic analyses on the spectral response and micro/nano structure characterization were reported. Spectrum shifting effect corresponding to color change was explained through surface plasmon resonance mechanism. The current research demonstrates that a high power and high repetition rate ps laser is capable of forming sequential colors on steel surfaces with a processing speed up to several meters per second, making this technology an efficient and affordable candidate for practical industrial applications. The research can pave the way for ps laser surface texturing technique to be applied to colorize conventional engineering materials.