Pulse-by-pulse evolution of surface morphology driven by femtosecond laser pulses

Abstract

Surface morphology is a key factor that determines the quality of laser-based micromachining processes. However, the governing laws of surface morphology in the laser processing process are yet to be clarified, and optimization of processing parameters has to rely on trial and error. Specifically, under multiple-pulse irradiation, it has been difficult to quantify the evolution of the surface morphology because the surface morphology changes with each pulse irradiation, and the ablation process changes accordingly. In this study, we investigated the evolution of surface morphology under femtosecond laser irradiation. Copper and silicon were used as targets, whose surface morphology changes exhibited seemingly opposite behaviors with respect to fluence. Using thousands of datasets, we obtained an evolution equation for surface morphology in terms of surface area, which acts as a good probe of the residual surface energy after ablation. Our model successfully quantifies the cumulative effect of multiple-pulse irradiation on surface morphology changes.