Full-Color Femtosecond Laser Painting on Titanium Films at 35000 DPI Resolution

We demonstrate high-resolution structural coloring of titanium thin films using femtosecond laser irradiation at visible (515 nm) and near-IR (1030 nm) wavelengths. By fabricating a novel Ti-TiO₂-Ti multilayer structure optimized for oxidation with ultrashort laser pulses, we achieve a full spectrum of colors with an ultimate sub-500 nm feature size and a maximal resolution of up to 35000 dpi. A systematic study reveals a key trade-off: while visible light enables higher resolution due to tighter focusing, near-IR radiation supports a more controllable and stable oxidation process, yielding a wider and more vivid color palette. Optical simulations attribute this superior performance of the near-IR light to a more homogeneous absorption profile that is maintained throughout the oxidation process. Finally, we highlight the practical value of our approach by demonstrating scalable multilevel structural coloring as well as hidden information encryption using natural anisotropy of the locally produced nanogratings with a facile scattering signal readout.