Multipulseffekte beim Mikro-Materialabtrag von Stahllegierungen mit Pikosekunden-Laserpulsen

Description

In the present thesis, a model-based method is presented to increase ablation efficiency of picosecond pulsed laser structuring. This method considers multi-pulse effects during laser-based micro structuring and the usage of flat-top beam shaping. For material removal of steel alloys, reasons and effects of pulse number depending ablation behavior called incubation were investigated. The analyzed reduced reflectivity of the substrate surface, which was already processed, represents one reason for decreasing ablation threshold at higher number of laser pulses. The energy penetration depth, which decreases with increasing number of pulses, affects incubation to the same extent. Digital holographic beam shaping by means of a liquid-crystal-on-silicon based spatial light modulator was investigated, aiming at the flexible adaption of the spatial intensity distribution. It has been shown, that the shaped homogeneous flat-top profile can be simulated when aberrations of the optical setup are considered and the range of spatial frequencies during beam shaping is enlarged. The geometry of the generated micro features was calculated by the presented model, which is based on the simulation of the intensity profile and the analyzed multi-pulse effects. For this purpose, pulse number depending variation and saturation of the ablation threshold as well as the energy penetration depth were implemented within the model.