Colorizing of the stainless steel surface by single-beam direct femtosecond laser writing

This paper reports on the colorizing of the stainless steel surface by controlling the irradiation conditions of a single-beam femtosecond laser. We change the color of the stainless steel surface by femtosecond laser induced periodic self-organized nanogratings or microgratings on the sample surface. Colorizing of metal surface by periodic microholes, produced by femtosecond laser, is achieved for the first time. The laser modified stainless steel surfaces show different colors under different incident or azimuthal angles of the incident light, which changes in color indicate the dependence of the metal color on the angles (incident and azimuthal) of the incident light. We report, for the first time, the changes of metal color due to the change of the azimuthal angles of the incident light. Furthermore, the changes in the color of the laser modified metal surfaces are mainly due to the excitation of surface plasmon polaritons (SPPs) on the metal surface. The resonant angle of SPPs is different for different wavelength of light. As a result, under different incident or azimuthal angles different wavelength of light is trapped on the surface depending on the resonance for that particular wavelength; light of other wavelengths react naturally and contributes for the color change of the stainless steel surfaces. Finally, we discovered that the nanostructures produced inside the self-organized nanogratings and microholes play important roles for the propagation of the SPPs in parallel with the nanogratings and mcroholes, which nanostructures are responsible for a complex SPPs excitation on the sample surface.