Crown-like structure development on titanium exposed to multipulse Nd:YAG laser irradiation

We report micrometre-sized crown-like structure growth on a Ti surface by multipulse Nd:YAG (λ=1.064 μm,τ=170 ns) laser irradiation in air at atmospheric pressure. The irradiation was performed at 8×107 W/cm2 laser-pulse intensity, below the ablation threshold. A ring-shape structure develops in the centre of the irradiation spot after the action of five laser pulses. The further increase of the laser-pulse number leads gradually to a crown-like structure, which has, for 150 pulses, a height of 120–140 μm above the non-irradiated Ti surface. The forming crater’s depth does not exceed the height of the grown structure. In the neighbouring zone, after the action of 25 laser pulses, microcracks of the oxide surface layer develop. With the next pulses this leads to the formation of a surface microrelief. The crown-like-structure growth is originated by molten material movement attributed to the laser-induced plasma-recoil pressure.