## 3 Results  
### Single-Pulse-Burst Craters  
For the PC samples, a low number of pulses was first tested, beginning with \(N=1\) and rising up to 100 pulses at a relatively high laser powers (\(p=40\) to 78 mW). A representative image of this experimental series is shown in Figure 2a. All the produced craters in this experiment series showed the same structure inside the crater and no structure around the crater. The inside shows an irregular sponge-like structure, like the one observed later with extruded CAB, with a high surface area. With lower laser powers (range \(p=8\) to 20 mW), the number of pulses was increased to compensate for the reduction in laser power (\(N=500\) to 1000). In this parameter range, we found that our PC samples showed laser-induced periodic surface structures (LIPSS). In some cases, both LIPSS variants (as described, for instance, in [13]) could be observed on the same sample: (1) high-spatial-frequency (HSF) LIPSS inside the crater and at the edge; (2) low-spatial-frequency (LSF) LIPSS appearing faintly in a first ring around the crater (orientated approximately perpendicular to the HSF-LIPSS), followed by a second ring of debris. In Figure 2b, the ring containing the LSF-LIPSS can be seen in between the two added red circles. For \(p=11\) mW and \(N=500\), a similar result was observed. Details from Figure 2b can be seen in Figure 2c,d. Figure 2c is a zoom-in, where an area covered with LSF-LIPSS, which was before located between the two red circles, is better visible. In Figure 2d, the HSF-LIPSS can be clearly seen in the bottom left corner, and LSF-LIPSS are visible in the neighboring areas to the right and above. These two structures together are only observed in fs-laser processing. They form perpendicular to one another. Please note that the LSF-LIPSS are shallow and rather indistinct. The power range in which the structures could be observed was small (\(p=11\) mW with \(N=500\) or \(750\) to \(p=15\) mW with \(N=500\), corresponding to a peak fluence range from \(F_{0}=0.92\) to \(1.25\) J/cm\({}^{2}\)). At  
Figure 2: SEM images of single-burst craters on PC with (a) \(p=50\) mW, \(f=1\) kHz, \(N=50\) and \(F_{0}=2.09\) J/cm\({}^{2}\) and (b) with \(p=11\) mW, \(f=1\) kHz, \(N=750\) and \(F_{0}=0.92\) J/cm\({}^{2}\). The images (**c**,**d**) are zoom-ins of image (**b**) at two different positions and with two different magnifications. In image (**b**), faint LSF-LIPSS are visible in the area between the two red circles, which are more obvious in the zoom-in in image (**c**). In image (**c**), the red arrow points to an area with LSF-LIPSS which was previously located between the two red circles, and in image (**d**), the red arrow points to an area with HSF-LIPSS at the edge of the crater. laser powers below \(p=10\) mW, only the HSF-LIPSS inside the crater could be observed, as well as with powers above \(p=15\) mW. Figure 3 shows a typical image of the structures inside a single-pulse-burst crater in this parameter range. Here the nominal laser power was \(p=8\) mW and the focus position was about \(50\) um below the surface of the PC sample. Only a part of the surface is covered with HSF-LIPSS. Interestingly, the HSF-LIPSS form preferentially on some terraces within the irregular sponge-like structures. For the extruded CAB samples, several craters with different number of pulses were achieved using the pulsed mode of the laser setup. Figure 4 shows a typical crater with a diameter of \(40\) to \(45\) um, which is already quite small. The diameters of the craters can vary significantly for this material (e.g., \(p=13\) mW resulted in diameters from \(20\) to \(50\) um). Inside, the craters show a sponge-like structure without spatial regularity. This structure could be observed in power ranges from \(p=12\) to \(18\) mW. Below \(p=10\) mW, the craters are slightly bigger but show a smooth surface, indicating that the sample is melting during the structuring process. A laser power increase here also increased the depth of the craters.