Generation of tailored picosecond-pulse-trains for micro-machining

Abstract

Novel solid-state picosecond lasers provide a strong benefit for high precision micro-machining. Pulse repetition rates as high as > 500 kHz with pulse energies of > 4 µJ enable fast machining with the precision of low fluence ablation. In addition, new potentials for these lasers are given by advanced modulators with digital timing control that allow the user to generate sequences or groups of pulses: E.g. a sequence of two pulses can be generated and repeated up to 300 kHz. The amplitude of these two pulses can be adjusted independently and the delay is selectable in 20 ns steps. This kind of pulse-strategies with picosecond lasers can support higher ablation rates, similar to the machining results that were demonstrated with double ns-pulses, recently. In another application, groups of > 20 pulses were repeated with > 50 kHz for ultra-precise machining. The distribution of the energy yields a few hundred nJ per pulse and results in an ablation depth per pulse in the range of several nm. Therefore the ablation depth formed by a group can be digitally controlled by the number of pulses in group. Samples for high quality drilling, cutting and structuring of several materials will be presented and the new potentials of this kind of picosecond laser processing with improved precision and speed will be discussed.

Six 38.7 W pulses in a burst of pulse-burst picosecond 1064 nm laser system at 1 kHz

“…In the amplification process, the pulses in front of bursts consume more gain, and so amplitudes of pulses in bursts would gradually decrease [5,13,18] . Here, by slightly adjusting the intensity of the pump and the rotation angle of the QWP (Fig.…”

“…Ultrashort pulse-burst picosecond lasers have been widely used in the production of equipment for x rays, industrial processing, communications engineering, biology sciences, and other fields [1][2][3][4][5][6][7][8][9] . High-energy pulse-burst picosecond lasers with a narrow pulse spacing are good x ray spectrum transform pump sources [1][2][3] .…”

“…Since the speed of light is faster, the geometric space would be much larger for this. An optical switch device was another method for choosing pulse bursts with high PRFs [4,5] . In terms of precision processing, Nebel et al [5] reported a single pulse energy of 100 nJ for pulse bursts of 2, 10, and 20 pulses by controlling the high voltage of Pockels cells (PCs).…”

“…An optical switch device was another method for choosing pulse bursts with high PRFs [4,5] . In terms of precision processing, Nebel et al [5] reported a single pulse energy of 100 nJ for pulse bursts of 2, 10, and 20 pulses by controlling the high voltage of Pockels cells (PCs). Owing to limitation of the response time of high voltage optical switch-offs, the pulse spacing was mostly more than nanoseconds.…”

“…When it was irradiated on an aluminum slab target at a peak pump intensity of 1.0 TW∕cm 2 , a time-integrated small signal gain coefficient of 1.7 cm −1 was observed at 300 μm from the target surface for a 154.7 Å Li-like Al laser, and the effective ablation rate was calculated to be ∼30 mm 3 /min [2] . Manufacturing processes using picosecond lasers generate less heat and have high precision, so they are applied in the manufacturing of several materials and are commonly used in micro and nanoprocessing [4,5] . A pulse burst can effectively reduce the threshold and improve the processing speed, so it has a better effect compared to a single pulse.…”