Burst-mode femtosecond laser coloring on pure titanium products

Coloring on pure titanium without toxic chemicals or thermal distortion remains a key challenge for consumer products. Here, we introduce burst-mode femtosecond laser processing that tailors oxide growth on the titanium surface by varying the number of sub-pulses within each 400 kHz burst. We observe a continuous transition from muted, low-saturation hues to vivid, uniform colors as the sub-pulse count gradually increases from 1 to 10. This evolution arises from the synergy between ultrafast non-thermal oxidation and gentle heat accumulation, which progressively smooths the oxide surface and suppresses iridescent microstructures. The resulting colors are free of electrolyte residues and the underlying titanium retains its original flatness. The technique thus offers an acid-free and maskless route for high-resolution decoration of pure titanium products.