Combined experimental and theoretical investigation of multiple-nanosecond laser ablation of metals

A detailed understanding of the physical determinants of the ablation rate in the multiple-nanosecond regime is of key importance for technological applications. Here, experiments and theoretical modeling are employed to investigate the ablation of thick aluminium plates produced by intense, multiple-nanosecond laser pulses. Opto-acoustic experimental measurements indicate that the ablation rate decays exponentially with the number of consecutive laser pulses. To understand in detail this behavior, we developed a theoretical photo-thermal model in which the complex phenomena associated with laser ablation are accounted for as supplementary terms in the classical heat equation. The ablation is considered as a thermal evaporation process induced by laser-absorption into the sample. Ablation rate decreases with the number of laser pulses due to reduction of the incident laser intensity with lateral area of the drilled hole. The photo-thermal model proposed here is validated by the good agreement between the experimental and the theoretical ablation rate that is obtained by integrating numerically the heat equation.