Colorization of copper surfaces by nanostructure modifications with ultrashort laser pulses

Abstract

A colorization of copper surfaces after nanostructure modifications with ultrashort laser pulses was studied. Femtosecond laser has been used for experiments. A relative motion of the laser beam on the material was realized. Tracks on the material obtained in a multi-pulse mode with an energy density lower than the threshold ablation were studied using scanning electron microscopy and atomic force microscopy. By the surface treatment with a laser pulses duration smaller than 30 fs, almost-wavelength periodic structures were formed and finally the surface brightness was increased. It was demonstrated that small nanostructure modifications changed the surface colour significantly. Using backscattered and secondary electron modes of scanning electron microscopy images were obtained from four sample regions that showed different colours, such as dark purple-red, turquoise, yellow-orange and grey-green. It was found that one of the main reasons for the difference in colour of images is the oxidation degree.