New random trigger-feature for ultrashort-pulsed laser increases throughput, accuracy and quality in micromachining applications

摘要

For most micromachining applications, the laser focus has to be moved across the workpiece, either by steering the beam or by moving the workpiece. To maximize throughput, this movement should be as fast as possible. However, the required positioning accuracy often limits the obtainable speed. Especially the machining of small and complex features with high precision is constrained by the motion-system's maximum acceleration, limiting the obtainable moving spot velocity to very low values. In general, processing speed can vary widely within the same processing job. To obtain optimum quality at maximum throughput, ideally the pulse energy and the pulse-to-pulse pitch on the workpiece are kept constant. This is only possible if laser-pulses can be randomly triggered, synchronized to the current spot velocity. For ultrafast lasers this is not easily possible, as by design they are usually operated at a fixed pulse repetition rate. The pulse frequency can only be changed by dividing down with integer numbers which leads to a rather coarse frequency grid, especially when applied close to the maximum used operating frequency. This work reports on a new technique allowing random triggering of an ultrafast laser. The resulting timing uncertainty is less than ±25ns, which is negligible for real-world applications, energy stability is <2% rms. The technique allows using acceleration-ramps of the implemented motion system instead of applying additional override moves or skywriting techniques. This can reduce the processing time by up to 40%. Results of applying this technique to different processing geometries and strategies will be presented.