Femtosecond Laser Ablation in Burst Mode as a Function of Pulse Fluence and Intra-Burst Repetition Rate

Abstract

Ablation rates were measured in burst mode operation for 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 and 250 kHz. Burst mode operation allows operation near the optimum fluence for laser ablation, thus maximizing the ablation rate. Depending on the 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 compared to non-burst operation. For metals and large area ablation, burst mode operation enables ac-cess to the maximum ablation rate by using more than 5 pulses per burst. Intra-burst repetition rates higher than 180 MHz, or using less than 5 pulses usually leads to a decrease in ablation efficiency due to shielding by the ejected material/plasma. For materials with low thermal conductivity, like glasses or plastics, and for semiconductors materials, interaction between burst pulses can substan-tially increase the maximum ablation rate over the 1-pulse case, leading to more efficient ablation as the number of burst pulses and the intra-burst frequencies are increased.