Mechanisms of Laser-Material Interaction in Microsecond Laser Ablation using a CW Single-Mode Fibre

Mechanisms of Laser-Material Interaction in Microsecond Laser Ablation using a CW Single-Mode Fibre


Laser ablation with pulse durations in the microsecond range is a viable solution for applications that require large MRR with moderate hole quality. The purpose of this investigation is to examine, both experimentally and theoretically, the laser-material interaction mechanisms during microsecond laser ablation using a 300W, CW single-mode fibre laser with modulation control. The experimental portion of the investigation includes improved laser control and ablation tests. Many in-process monitoring such as photodiode measurements of the vapour intensity, high-speed photography, and spectroscopic plasma measurements were conducted. The theoretical portion is a thermo-hydrodynamic model that considers beam absorption due to multiple reflections, vaporization-induced pressure, and heat convection in the melt, and the free surface at the liquid-vapour interface. Due to very high irradiance of the fibre laser beam, the absorbed energy not only is sufficient to melt and vaporize the material, but also is able to dissociate vapour into intense plasma. The hole drilling by microsecond laser ablation is due to a combination of adiabatic evaporation and ejection of fine droplets. This paper describes the interactions between the bulk material, the laser beam, and the vapour/plasma and a process anatomy is presented to describe the temporal behaviours of these interactions.