Micro-milling process improvement using an agile pulse-shaping fiber laser

摘要

We demonstrate the usefulness of INO's pulse-shaping fiber laser platform to rapidly develop complex laser micro-machining processes. The versatility of such laser sources allows for straightforward control of the emitting energy envelop on the nanosecond timescale to create multi-amplitude level pulses and/or multi-pulse regimes. The pulses are amplified in an amplifier chain in a MOPA configuration that delivers output energy per pulse up to 60 μJ at 1064 nm at a repetition rate of 200 kHz with excellent beam quality (M~2 < 1.1) and narrow line widths suitable for efficient frequency conversion. Also, their pulse-on-demand and pulse-to-pulse shape selection capability at high repetition rates makes those agile laser sources suitable for the implementation of high-throughput complex laser processing. Micro-milling experiments were carried out on two metals, aluminum and stainless steel, having very different thermal properties. For aluminum, our results show that the material removal efficiency depends strongly on the pulse shape, especially near the ablation threshold, and can be maximized to develop efficient laser micro-milling processes. But, the material removal efficiency is not always correlated with a good surface quality. However, the roughness of the milled surface can be improved by removing a few layers of material using another type of pulse shape. The agility of INO's fiber laser enables the implementation of a fast laser process including two steps employing different pulse characteristics for maximizing the material removal rate and obtaining a good surface quality at the same time. A comparison of material removal efficiency with stainless steel, well known to be difficult to mill on the micron scale, is also presented.