In-Situ Analysis of Heat Accumulation during Ultrashort Pulsed Laser Ablation

Ultrashort pulse (USP) laser processing with pulse durations below 10 ps enables laser structuring with good surface quality, highest precision and low thermal load for the processed workpieces. However, when it comes to scale up the productivity of such processes by increasing the average power, accumulation of the remaining residual energy gets relevant and can influence the processing results significantly. For instance, heat accumulation can induce distinct melt layers. Thus the melt-free, high precision ablation, which is the main advantage of USP processing, is compromised. This is especially pronounced for high repetition rate processes. For a better insight into this effect, the development of the workpiece temperature during USP ablation processes is measured with a thermographic system. With this setup, the residual energy is determined and changes of the heat input during the processing time are identified. These changes are attributed to changes of the surface roughness during the processes within this work. Furthermore, the validity of simple physical model considerations is discussed. Keywords: ultrashort pulsed ablation, heat accumulation, residual heat, high repetition rate, thermographic, in-situ, ultrafast laser ablation