Continuous GHz femtosecond laser interacting with aluminum film: Simulation and experiment

Abstract

GHz femtosecond laser has attracted more research interest due to the so-called high-efficiency cold ablation effect. In this study, behavior of continuous GHz (cGHz), i.e., GHz repetition frequency femtosecond laser with no burst mode, interacting with aluminum (Al) film has been investigated numerically and experimentally. For this purpose, an axisymmetric two-temperature model was used, accounting for the thermodynamical evolution of Al film. Laser irradiating Al film experiments were also carried out simultaneously. The calculated temperature field evolution was in good agreement with the observed experimental results. Effects of laser fluence and scanning speed on morphology, area, height, and volume of the residual Al film were then sequentially studied. Interestingly to see, for this cGHz femtosecond laser source, melting and re-solidification lead to the material removal under low laser fluence, say, ≤0.0337 J/cm2 in this study. For the whole Al film, with laser fluence increasing, the outmost lattice evaporation and beneath lattice melting occur together, both responsible for material removal and morphology variation. Finally, a potentially beneficial GHz femtosecond laser mode for high-quality microfabrication is proposed.