We investigated the process of laser micro-drilling of copper and iron by using nanosecond laser-pulses at 532nm
wavelength in atmospheric air. We analyzed the ablated volume, ablation rate, crater diameter, and craters quality as
functions of laser-fluence and beam-diameter. The fluence was varied between 10 and 6000 J/cm2 by changing the laserenergy.
The results indicate that the ablated volume increases linearly with fluence, whereas the ablation rate and crater
diameter increase linearly with the fluence's square root. The ablated volume, ablation rate, and crater diameter, increase
with thermal diffusivity of the materials. Additionally, the ablation threshold-fluence is demonstrated to be directly
related to the optical penetration depth.
The ablated volume, ablation rate, and crater diameter were further assessed for beam-diameters in the range of
10-50 microns by translating the targets away from the focal plane while keeping a constant fluence. The results indicate
that the ablated volume increases linearly with beam-diameter, whereas the ablation rate and crater diameter increase
linearly with the inverse of the beam-diameter's square root.
To investigate the craters quality we measured the dimension of the thermally affected zone (TAZ) around the
craters as a function of fluence. At fluences up to 400 J/cm2, where strong ionization occurs within the plume, the crater
diameter is <15 microns (comparable with beam diameter) and there is small TAZ around the craters. Further increase of
the fluence leads to a significant increase of TAZ, indicating that the expanding plasma plays a major role in metals
ablation in this fluence domain.