Residual heat during laser ablation of metals with bursts of ultra-short pulses

The usage of pulse bursts allows increasing the throughput, which still represents a key factor for machining with ultra-short pulsed lasers. The influence of the number of pulses within a burst on the specific removal rate is investigated for copper and stainless steel. Furthermore, calorimetric measurements were performed to estimate the residual energy coefficient as well as the absorptance of machined surfaces for copper to explain the reduced specific removal rate for a 2-pulse burst and the similar or even higher rate for a 3-pulse burst compared to single pulse ablation. Based on the measurements, a description of the process using single pulses and pulse bursts with up to three pulses is presented.

Investigation of Femtosecond Laser Ablation Threshold for Nickel Template

This paper presents a theoretical and experimental investigation into the ablation threshold of nickel template by femtosecond laser in air at atmospheric pressure. The laser pulses used for the study are 800 nm in wavelength, 100fs in pulse duration, and 1KHz in repetition rate. The two-temperature model is used to predict the single-pulse ablation threshold for nickel theoretically. Micro-hole ablation experiments are carried out in air by focusing the femtosecond laser beam on the nickel target surface at normal incidence with the long-focus objective lens of enlargement factor 50 and NA=0.7 to determine the single-pulse and multi-pulse ablation thresholds for nickel by setting up the relationship between the measured hole diameters and the pulse energies. The single pulse ablation threshold of 4132.98 Jm-2obtained experimentally is very close to that of 3907.99 Jm-2predicted by two-temperature model. The incubation factorξ, which describes the changes of the multi-pulse ablation thresholds with the number of pulses, is determined to be 0.812 for nickel.