Microstructuring using femtosecond pulsed laser ablation

A self-induced mechanism leading to the formation of periodic microstructures has been observed during femtosecond pulsed laser ablation with a high repetition laser source. The bottom of an ablated area shows two different kinds of microstructures. A periodic ripple or a chaotic columnar structure emerges. It has been observed that the second morphology grows out of the first one dependent mainly on the amount of fired laser pulses. This transition and the influence of several parameters on it are described. Both structures have several variations in morphology. Regarding the possible applications of such structures, this is of special interest. The presented experiments give a first glimpse of the possible microstructures emerging after ultrafast laser machining. Concerning the physical background of the found phenomena, it has been observed that a liquid phase is present in the ablation process. The formation of ripples may be closely linked to that fact. Existing models on ripple formation could not be linked to the ripple spacing found in the experiments.