Plasma mediated ns-laser erosion of SiC monitored using Raman spectroscopy and in-operando LIBS

In this study, the mechanism of nanosecond laser-assisted material erosion is revealed to be dominated by multiphoton absorption and material ejection in a gaseous plasma plume. The role of ambient gas (air or argon) in plasma removal is also reported. When cutting in air, the fact that fewer debris are found after the bigger hole forms suggest that oxygen assists material removal as gaseous products. In support of this preliminary hypothesis, the ablation mechanism was studied using a unique Raman microscope, with co-located nano-mechanical scratch testing, and with In-situ laser-induced breakdown spectroscopy (LIBS). From this it was confirmed that oxygen and nitrogen in air helps to gasify carbon in a plasma plume containing Si+, C₂ radical CO₂, CO, and CN. It was also confirmed that the structure of the ablation debris are sedimentary, with carbon network deposits overlaying Si deposits (Raman maps). The underlying SiC is in good condition with no residual stress as the ablation debris are loosely bound and can be removed by shear force. Therefore, the actual heat-affected zone is minimal. Thus, effective and clean laser cutting can be conveniently achieved with plasma-mediated erosion, in air. However, narrower cuts are best achieved under Ar.