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A spectroscopic and theoretical study of the laser ablation rate of Al

We investigated experimentally and theoretically the laser ablation of Al by using nanosecond laser-pulses at 532 nm wavelength in atmospheric air. We analyzed experimentally the dependence of the ablation rate on the laser fluence and pulse number. The fluence was varied between 3 and 3000 J/cm2 by changing the laser-energy, while pulse number was varied between 4 and 60 in steps of 4. The optical microscopy data indicate that the ablation rate increases approximately linearly with the 1/3 power of the fluence. For high fluences (hundreds of J/cm2) the ablation rate is demonstrated to be very large (~2 micron/pulse) and approximately constant during 30 consecutive pulses and much smaller during the next pulses. The dependence of the ablation rate on pulse number was further addressed by spectrometric analysis of the ablation-plasmas produced at high fluences. We found that the plasma temperature varies similarly to the ablation rate when increasing the pulse number. The ablation rate in the low fluence regime was addressed theoretically within the frame of a photo-thermal model which accounts for the material heating, melting and evaporation upon laser radiation. The theoretical and experimental results are in good agreement indicating the validity of the model for low laser fluences.