Microstructuring of polymer films by femtosecond pulses through optically trapped polystyrene microspheres

We report the laser ablation of polymers by femtosecond (18 and 54 fs) pulses focused by 1 and 3.8 μm diameter spherical microlenses, which are held by optical traps. It is shown that this technique allows one to produce surface structures with lateral dimensions up to λ/6 (125 nm). It is found that the size of the structures depends on the diameter of the microlens; the highest spatial resolution is achieved by using 1 μm diameter microlenses.