Experimental study on the laser-matter-plume interaction and its effects on ablation characteristics during nanosecond pulsed laser scanning ablation process.

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Nanosecond pulsed lasers have been widely applied to interact with and characterize many different materials. For the purpose of a broader application, the current challenge is to achieve a speedup of ablation process, which is commonly thought to be possible by raising the on-target laser intensity. But the use of high intensity lasers results in severe laser-matter-plume interaction, leading to unwanted effects (e.g. saturation, shielding and thermal damage), which further affect the ablation process and ablation quality. However, laser-matter-plume interaction and its effects on ablation characteristics during laser scanning ablation processes are not well understood. In this paper, shadowgraph images and optical images during a laser ablation process were taken with a pump-probe shadowgraph imaging setup and an ultrahigh-speed camera. The results demonstrate that, under a high incoming laser density, laser-matter-plume interaction presents a periodical process, and thus cause a major impact on ablation regimes and microstructure formations. Moreover, the characteristics of micromorphologies and ejected particles suggest that the laser-matter-plume interaction has a significant influence on the ablation process, which, in turn, provides a more comprehensive understanding of the influence of laser-matter-plume interaction on the scanning ablation process. Consequently, laser-matter-plume interaction and its influence on the ablation process were summarized and clarified.