## 3 Results  
Different patterns created by direct laser writing (DLW) on the Ni/Al reactive foils are presented exemplarily in Figure 1. The shape seen in Figure 1d was the one selected for the microstructural characterization carried out in this work. For all samples, the lines were cut through the total thickness of the film. Figure 2a-c shows SEM micrographs of the cut region of the three different samples, and it is possible to see that the amount of debris varies among the different laser parameters. Furthermore, the 150 fs_1 kHz sample (Figure 2b) appears to have the smoothest cut line, while the other two samples exhibit a more irregular edge profile. The width of the debris deposition before cleaning can be seen in Table 2. Among the samples examined, the one with the most extensive debris was 150 fs_1 kHz, while the sample with the smallest amount of debris, and thus the cleanest cut, was 150 fs_5 kHz. After cleaning in an ultrasonic bath, the debris region outside the trenches was completely removed and was considerably reduced on the inside. EDS measurements were performed to qualitatively determine debris composition. The acceleration voltage was limited to 5 kV to have most of the excited volume close to the sample surface. Figure 2d shows the spectra of an unstructured reference area and of the debris. The reference spectrum of an untreated region mainly shows signals of silver, copper, and indium, as could be expected due to the InCuSil layer. No signal of aluminum or nickel can be seen, which means that the electron interaction volume is confined in the InCuSil layer. The debris exhibits strong signals of oxygen, nickel, aluminum, and carbon and minor signals of silicon, sulfur, and silver. Silicon and silver are constituents of the InCuSil layer that covers the RMF in the as-received state. The signals of silver and copper in the blue curve (150 fs_5 kHz) hint to a thinner debris layer, so the underlying InCuSil coating could be excited as well. The presence of traces of sulfur could be attributed to the tendency of silver to react with traces of atmospheric sulfur. Oxygen being the dominant peak in the spectrum indicates that the debris is of oxidic nature, whereas nickel and aluminum signals are evidence for the debris being redeposited material from the trench. The source of carbon is unknown. \begin{table}
\begin{tabular}{c c c} \hline
**100 fs\_1 kHz** & **150 fs\_1 kHz** & **150 fs\_5 kHz** \\ \hline
49.29 \(\pm\) 1.58 μm & 83.73 \(\pm\) 1.23 μm & 26.23 \(\pm\) 0.83 μm \\ \hline \end{tabular}
\end{table} 
Table 2: Extent of the debris and oxide layer present outside the lines cut by the laser for the different laser parameters. Figure 1: Different shapes created by DLW on the Ni/Al RMF. (**a**) Single hole, (**b**) double C, and (**c**) comb, all cut at 100 fs and 1 kHz; (**d**) single lines, cut at 150 fs and 1 kHz. The area structured is 16 mm\({}^{2}\) for all samples, and all lines and holes penetrated through the 40 μm thickness of the foil. The inner structure and thickness of the debris zones was investigated in FIB cross sections. Figure 3a shows an overview of the cross section extending from the cut edge (left) over the full width of the debris zone of sample 100 fs_1 kHz. A continuous decay of debris thickness can be seen. Figure 3b shows a detailed view of the edge at the transition from the ablation zone of the laser trench to the oxidic debris on the surface. The latter is porous, with a thickness of 4.85 um at the highest point close to the ablation zone. The presence of the undamaged InCuSil layer between the oxide and the RMF indicates the transition from direct layer ablation to a region of debris redeposition. It becomes clear that this transition cannot be seen in a top-view micrograph as it is hidden under oxidic debris. Note that maximum debris layer thickness varies strongly among the samples, ranging from 4.85 um (100 fs_1 kHz) to 12.18 um (150 fs_1 kHz); however, the porous appearance does not change.