Micro processing with ultrafast bursts of pulses

Abstract

Ultrashort-pulsed lasers allow a precise, low thermal damage and material independent micro processing. However the full potential of ultrashort pulsed lasers with their currently available laser power cannot be used due to limitations in ablation rate per pulse keeping the high quality in ablation. Beside scaling up by multi spot technology, the application of ultrashort pulse bursts is another possibility to increase the ablation rate. In this paper a newly developed ultrashort pulsed laser with a seeder frequency of 500 MHz has been investigated in cylinder micro engraving application. The laser offers the possibility to control the shape of a burst sequence in amplitude and timing. The influence of the pulse sequence on the ablation rate and quality in combination with the different metals has been investigated. The pulse burst frequency has been changed between 1 - 5 MHz with a scanning speed of 16 m/s. The pulse to pulse overlap at the work piece was adjusted from 0% to 90%. Comparing to single pulse ablation the ablation rate with GHz pulse burst is increased by factor 2.2. The surface roughness is Ra = 0.38µm with GHz pulse burst, whereas the roughness is Ra = 1.423 µm with single pulse. In this paper experimental ablation results and quality aspects will be presented and discussed.