## 2 Experimental Methodology  
An Al-6061 orthogonal dry milled part, of an overall size of 10 cm \(\times\) 3 cm \(\times\) 0.9 cm, was the laser-irradiated target of our study. Figure 1a shows a schematic of the optical setup for the laser-irradiation experiments.  
The optical geometry for the laser-irradiation experiments is shown in detail in Figure 1a: The laser source used for the interaction with the Al sample is a pulsed laser source (6-ns pulse duration) emitting radiation of 0.7 mJ energy per pulse at 532 nm. The value of 0.6 mJ was the threshold below which no detectable effect was induced by the laser on the target surface. The output of the laser system is guided through metallic mirrors to a converging lens (\(f\) = 100 cm) and the beam is then focused onto the target surface. The profilometry setup is incorporated into the optical setup, as demonstrated in Figure 1a. It constitutes the final part of the geometrical arrangement and is used for the characterization of the samples before and after they were irradiated with the laser pulse. The advantage of the experimental configuration is that the position of the sample can be maintained without the necessity of any change, during both the interaction and the characterization measurements, and, therefore, the interaction area on the target surface can be well determined and studied. The profilometry configuration is based on a Michelson white light interferometer, described in detail in [7]. Briefly, a beam splitter separates the white light emitted from the source, generating the reference and object beams, the latter being reflected by the sample surface. A metallic mirror placed on a linear piezoelectric actuator is moved and used for altering the optical path of the reference beam. The two beams are recombined on a CCD camera, which is connected to a PC. A series of surface images and interferograms for the different positions of the moving metallic mirror are acquired and processed, allowing for the determination of the surface topology [7].  
A typical 2D grayscale surface image of the SA as extracted from the profilometry measurements is demonstrated in Figure 1b: The selected area imaged in this figure covered a length of \(x=3\) mm. The profile of the surface roughness plotted at the center of the selected area is shown in Figure 1c,d, using a roughness meter (Roughness gauge TESA Rugosurf 20) and the profilometry setup, respectively, for validation. It is worth noting that, even though the surface roughness topology was accurately determined by both techniques, profilometry offered the advantage of measuring the roughness at the exact region of interaction with the laser pulse, as already mentioned, but also the advantage of extracting an average line-out plot in contrast to the line-out from the roughness meter, which was taken along a single line. This average line-out plot resulted from averaging the roughness values of all the points within a selected area (yellow rectangular area) of the same \(x\) position and along the \(y\) axis. This way, the generated plot is representative of the overall surface of the original sample, eliminating effects from local discontinuities or measured artifacts. Such an average roughness plot was extracted from Figure 1b,d. In order to investigate the effect of roughness on the structural changes due to the laser, the laser spot was focused on the position of the maximum roughness variation (\(\sim\)3 \(\upmu\)m depth). The dimensions of the elliptical laser spot determined the area of interest, which covered a region of \(x=400\)\(\upmu\)m. The average roughness profile of this area (Figure 1e) was used as a pattern for the downscaling of the models.