Femtosecond laser ablation of Al-Mg alloy in vacuum and air

Ablation rates of Al-Mg alloy were studied as a function of laser fluences in air and vacuum. The central wavelength was 800 nm and the pulse duration was 35 fs. Three distinct ablation regimes were identified from the ablation rate curves. Ablation thresholds of 0.16 J/cm2, and 0.73 J/cm2 were obtained in the low and moderate laser fluence regimes, respectively. In the case of the third ablation regime, the ablation rate in vacuum is much higher than that in air, which may be due to the oxidation effects and strong defocusing effects associated with the non-equilibrium ionization of air. The damage threshold decreased with the increase of the pulse number, showing an accumulation effect. The fs laser ablated craters showed smooth edges, and laser-induced periodic surface structures (LIPSS) were observed around craters.