Efficiency of ultrafast laser ablation in burst mode as a function of intra-burst repetition rate and pulse fluence

Abstract

Laser ablation in burst mode enables operation close to the optimum pulse fluence of the material thus maximizing the ablation efficiency and reducing the heat affected zone. In addition, burst mode operation can enhance the ablation rate in some materials due to thermal interaction between burst pulses via the material. We have measured ablation rates for burst mode ablation on various materials (metals, semiconductors, dielectrics) as a function of pulse fluence, intra-burst repetition rate (60 MHz, 180 MHz, 360 MHz, 720 MHz, 1.44 GHz) and the number of pulses per burst (1-30), using a 40 μJ, 1035 nm Yb:Fiber MOPA with 300 fs pulse duration and repetition rates between 100 kHz and 250 kHz. The ablated geometries were rectangular cavities with side lengths of about 0.3 mm times 2 mm. The ablation efficiencies in burst mode operation are compared with the efficiencies that can be obtained with single pulse operation at high repetition rates and the same pulse fluence. Depending on material, number of pulses in the burst, intra-burst repetition rate and the ablation geometry, the ablation efficiency can be equal, lower or multiple times higher as compared to non-burst operation.