Development of a novel surface processing system using femtosecond pulse train

When a laser pulse interacts with metal or semiconductor target, the coherent phonon, which is the coherent motions of lattice and molecule vibrations in solids, is excited by the interaction of electrons and high latitude electric field. It has unique properties of decaying in approximately several picoseconds and substance specific frequency. Owing to that, femtosecond laser processing is the local processing with little heat diffusion and little thermal damage to the target, due to the ultrafast time scales. We propose a novel femtosecond pulse ablation process with oscillation of the coherent phonon by femtosecond pulse train. The pulse train is shaped using Spatial Light Modulator (SLM), which shift the phase of the passing light. And coherent phonon oscillations are enhanced and decayed due to the controlling the shape of pulse train. It is able to activate the lattice motion for processing efficiently, and hence the target is expected to be ablated with high accuracy and less thermal damage.