Effect of laser fluence on the ablation rate of metals in the infrared, visible, and ultraviolet nanosecond pulses irradiation regime Available to Purchase

We performed experiments to investigate the dependence of the ablation rate of three metals (aluminium, titanium and copper) on the fluence of nanosecond laser pulses at 1064, 532 and 355 nm wavelength in atmospheric air. We assessed the ablation rate for values of the fluence in the range of 1-600 J/cm² by changing the irradiated area at the target surface, while exchanging the harmonics modules of a Nd-YAG laser system to vary the wavelength. The data indicate that, at each wavelength, the ablation rate for the three metals studied here increases approximately logarithmically with the fluence. By analysing the logarithmic dependence of the ablation rate on fluence, we find three main characteristics that describe metal ablation in nanosecond regime. First, the ablation threshold fluence is directly related to the optical penetration depth, which depends on the irradiated material and wavelength. Second, the ablation rate decays with the optical penetration depth and thermal diffusivity of the material, the aluminium ablation being the most efficient. Third, the ablation rate of metals increases with increasing laser wavelength. The increase of the ablation rate with wavelength is related to the superposition of two effects: the increase of plasma absorption with wavelength, which leads to an enhanced recoil pressure on the melted surface of the target, and the increase of the evaporation and melt ejection rates due to the large recoil pressure.