| Abstract [eng] |
Efficient Laser Ablation of Metals Using Ultrashort Bursts: Drilling and Milling The need for various microstructures in different materials increases because of the rapidly improving technologies. This need is met mostly by laser micro-machining, which is a fast, precise and universal method. Ablation efficiency depends on many laser parameters, such as: average laser power, pulse repetition rate, pulse duration, pulse overlap and others. Several experiments were carried out in this work, during which a state-of-the-art laser was used. This laser was able to work in burst and bi-burst regimes, which were used to find a set of optimal parameters for the highest ablation efficiency in laser drilling and milling processes. During the experiment the pulse number in the burst and bi-burst regimes were changed. The pulse duration was 210 fs, pulse repetition rate was 100 kHz and pulse repetition rate inside the burst was 64.68 MHz. If each of the laser pulses inside the burst consists of a burst themselves, then the mode was bi-burst. Pulse repetition rate inside the bi-burst mode was 4.88 GHz. Moreover, the beam waist radius was increased by moving the sample surface out of the focal position to change the fluence. The experiment was carried on two metals copper and stainless steel, that are frequently used in various industries. Using the burst regime, the ablation efficiency was increased by 10% on copper when 3 pulses were inside the burst. The ablation efficiency was increased from 5.3 μm3/μJ to 5.8 μm3/μJ, when the fluence was 2 – 3 J/cm2. The highest machining quality was also inside this fluence region, which corresponded to a surface roughness of 0.3 μm. Using the bi-burst method the ablation rate dramatically decreased. Ablation efficiency of 6.9 μm3/μJ was achieved on stainless steel. However, no further improvements were seen while using burst and bi-burst regimes. During laser drilling on copper the ablation efficiency was increased by 16% from 7.6 μm3/μJ to 8.8 μm3/μJ when 3 pulses were inside the burst. Laser drilling was 50% more efficient than laser milling due to the more favorable ablation mechanism. |
