Controlled through-hole ablation of polymer microspheres

We report on ablation of complex micro-patterns on/in polymethylmethacrylate (PMMA) microspheres of 2–7µm diameter. By controlling the irradiation fluence, different ablation patterns can be reproduced: (i) the ablation of the opposite side to that irradiated, (ii) two-side ablation along the propagation of the beam and (iii) a through-hole ablation of the PMMA microsphere. Microspheres were laser trapped and held by tightly focused cw-illumination at 1064 nm while the ablation was carried out by a coaxial irradiation of a single laser pulse of 7 ns duration at 355 nm wavelength. Calculations of spatial intensity distribution of Mie light scattering by a laser-trapped microsphere corroborated the ablation patterns observed experimentally. Laser microfabrication of through-holes in microspheres is explained by the ablation-triggered shock waves. The ponderomotive action of the laser beam is discussed.