Enhanced multiple pulses incubation of high-repetition-rate femtosecond laser via seed guidance

Abstract

Multiple pulses incubation based on defects accumulation in laser processing can reduce material ablation threshold and improve machining accuracy, but the randomness of the laser-induced defects leads to unstable incubation. Here, the enhanced multiple pulses incubation strategy of a high-repetition-rate femtosecond laser via seed guidance is proposed to improve machining accuracy. The stable multiple pulses incubation is attributed to a pre-designed seed at a laser processing starting point and a high-repetition-rate femtosecond laser being used. A defect called seed is first prepared on the substrate at a high laser fluence, which significantly increases the absorption of subsequent laser pulses energy. Taking the seed as the starting point of laser processing, subsequent pulses can realize laser ablation at a much lower laser fluence and create new seeds. With the multiple pulses irradiation of the high-repetition-rate femtosecond laser, the stable incubation is finally realized by forming cascade seeds along the scanning path. The material ablation threshold is significantly reduced via the enhanced incubation effect. At a lower laser fluence, the fabricated size is reduced from ∼2.5 to ∼0.7 μm on a silicon substrate. Using this strategy, high-performance reflection grating and a superhydrophobic functional surface are fabricated on silicon substrates. Meanwhile, this strategy can also be extended to transparent material processing.