Effect of indirect irradiation on surface morphology of Au film by nanosecond laser

Indirect nanosecond-pulsed laser ablation of Au film of 10 nm–600 nm has been performed to investigate the ablated surface morphology of Au film as compared to direct pulsed laser ablation. This work shows that both the direct and indirect ablations give similar trend of ablation threshold fluence for film thickness equal or less than 170 nm. In this region, the ablation mechanism is driven by melting and vaporization. However, for film thickness greater than 170 nm, indirect ablation exhibits superior film quality with 3.0–3.6 factors less applied laser fluence compared to direct ablation and thus has no heat-affected zone and no recast material. As a result, the ablation mechanism for indirect ablation is driven by photomechanical process. This work highlighted the significant role of irradiation orientation (direct and indirect) as well as the correlation of heat penetration depth with different Au film thickness in influencing the ablation mechanism of Au film on glass substrate.