| Abstract [eng] |
The high throughput in the laser microfabrication is a key factor for most of industry companies. In this work the efficient laser ablation of stainless steel and copper with pico- and sub-nanosecond pulses was investigated. The model of efficient ablation was applied. It was demonstrated, that there is an optimum laser fluence point for maximum material removal rate. Using existing ablation model the influence of distance between pulses on sample surface and pulse overlap was calculated. It was shown that, when distance between pulses is zero or pulses overlap is 100 %, the most efficient material removal take place. In contrary, if distance between pulses increases the ablation rate drops down and reaches negative value at the point where beam spot is smaller than pulse distance. Experiments were carried out to find out the efficient ablation point by varying beam focusing conditions. All parameters were kept constant while beam focusing was varied to find optimum fluence. Experiments were done for two different pulse repetition rates: 100 kHz and 500 kHz in case of 13 ps pulse duration laser. It was shown that material removal rate reaches maximum at 10 J/cm2 for 100 kHz and 0.8 J/cm2 for 500 kHz while processing trenches. The efficient ablation of copper was investigated with 300 ps pulse duration laser machining cavities. It was found out that optimum fluence for copper was about 9 J/cm2. Using experimentally calculated optimum beam radius, the structure with increasing trench width was machined. The overall removal rate was reached of 10.2 µm3/µs while processing at the point far from optimum resulted in 7 times smaller material removal rate. Furthermore, surface roughness was 5 times smaller for trenches machined with optimum fluence. The efficient ablation model was investigated and the most important parameters concerning ablation rate were extracted: effective energy penetration depth, ablation threshold and optimum fluence. It was shown that material ablation rate can be easily increased if working wisely in optimum fluence range. Also, cavities machined with fluence around the optimum point had the smallest surface roughness. |
