Impact of assisting atmospheric pressure plasma on the formation of micro- and nanoparticles during picosecond-laser ablation of titanium.

In this work, we investigated the generation of particles during pure laser and plasma-assisted laser ablation of titanium. Experiments were performed using a NIR picosecond laser at a wavelength of 1030 nm and a pulse duration of 8 ps. For plasma-assisted ablation, an atmospheric pressure dielectric barrier discharge plasma was applied where the process gas was argon. Quantitative particle distributions at sizes from 10 nm to 10 μm were determined. In addition, we evaluated the amount of ablated material via laser scanning microscopy. The ablated volume was significantly increased by a factor of 2 to 3 in the case of plasma-assisted ablation, depending on the applied laser dose. It is shown that the increase in particle volume and number of particles was lower than the ablated volume. However, when applying plasma simultaneously, the generation of small nanoparticles increases notably by a factor of up to 6.63 at a laser dose of 0.7  kJ/mm for particles with a mean diameter of 10 nm. The results suggest that even smaller particles than measurable are generated. Hence, plasma-assisted laser ablation could enhance the process efficiency, reduce the particle agglomeration, and give rise to an increase in generation of nanoparticles at the same time.