Puls-zu-Puls-Wechselwirkungen beim Ultrakurzpuls-Laserabtrag mit hohen Repetitionsraten

The application of ultrashort pulsed laser sources with pulse durations inthe range of up to 10 picoseconds enables very precise materials processingwith negligible thermal load for the processed work pieces. While themachining quality is excellent, the comparable small productivity in termsof ablation rate is the main shortcoming that inhibits a widespread industrialapplication in many cases.Subject of this dissertation is the upscaling of USP laser ablation tohigher productivity by using average power of several hundred Watts whileincreasing the pulse repetition rates to several megahertz. Initially, theeffects that are limiting the upscaling process are identified and investigated.When using high repetition rates, these limiting effects are heataccumulation on the one hand and shielding by plasma or particle plumeson the other hand. Within the presented dissertation a theoretical model isdeveloped, which is capable of describing the impact of these two effects onthe achievable productivity. The high relevance of the two effects for theUSP laser ablation with high repetition rates is confirmed by experimentalresults. Heat accumulation is leading to the generation of melted and veryrough surfaces, which cannot be accepted for most applications. On theother hand, shielding effects lead to a decrease of the achieved productivityof up to 50 %. Therefore, these effects need to be considered when doingan upscaling by using high repetition rates. By comparing experimentalresults and the developed theoretical description, heat accumulation andshielding effects can be attributed to underlying physical quantities.On the basis of the developed process understanding, a significant increaseof the ablation rate to a value of more than 30 mm3/min is achieved forthe processing of Inconel 718. In addition to the approach of applyingfast scanning technology to use high repetition rates, a new approach ispresented. Based on the specific utilization of heat accumulation, it ispossible to achieve comparable high repetition rates at good surface qualityusing conventional, high flexible galvanometerscanners