Selective Ablation of Thin Films by Ultrashort Laser Pulses

Laser ablation of bulk solid could obtain superior machining accuracy by utilizing ultrashort pulses due to the smaller laser-induced thermal diffusion length, which minimizes the heat affected zone. In selective laser ablation of thin films, the precise control of the heat affected zone in the vertical direction becomes critical in order to avoid the damage of the substrate. For this application an effective thermal penetration depth can be defined determined by not only the optical penetration depth, but also the lattice thermal diffusion length in short pulse ablation or the hot- electron penetration depth in case of ultrashort laser ablation. The ablation characteristics, such as the threshold fluence and the multi-pulse incubation effect, are strongly dependent on the film thickness when it is in the range of the effective thermal penetration depth.