## 3 Results and Discussion
### Influence of the Number of Burst Modes Processed on Cutting Results  
Keeping the repetition frequency of the laser at 100 kHz and the energy at 11.5 W, the laser-cut samples were examined with the number of burst modes of 1, 2, 3, 4, and 5, respectively, and the results are shown in Figure 8. The concentration of energy in a single pulse results in relatively severe ablation of the sample cross-section near the upper surface area and incomplete modification of the sample near the lower surface area, as well as the appearance of a diagonal pattern. The overall modification was most uniform and effective when the number of burst modes was 2. After the first sub-pulse in the pulse train acts on the material surface, a large number of free electrons are generated due to ionization. As a result, the above factors led to significant changes in the optical properties of the material surface. After the first sub-pulse, the optical properties of the material surface changed. Therefore, when a second sub-pulse was applied after a certain pulse delay, the energy of the second sub-pulse was redistributed. This changed the light-absorption process, which in turn affected the electron density distribution. As the number of burst modes was further \begin{table}
\begin{tabular}{c c c} \hline \hline
**Incident Laser Power (W)** & \
\begin{tabular}{c} **Average Roughness of** \\ **Cross-Section (nm)** \\ \end{tabular} &
\begin{tabular}{c} **Maximum Difference in the** \\ **Regions (nm)** \\ \end{tabular} \\ \hline
8.4 & 185.92 & 7.33 \\
11.5 & 159.58 & 15.67 \\
14.2 & 204.83 & 13.33 \\
16.83 & 236.58 & 68 \\
19.01 & 315.5 & 98.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Table of average roughness of cross-section and maximum difference in the regions for different incident powers. increased, the energy distributed by individual pulses decreased, producing the effect of inadequate modification [22]. The cross-sectional retexturing varied as the number of burst modes increased, and the higher the number of burst modes, the larger the area of inhomogeneous retexturing, as shown in Figure 8 below. The morphology of local AFM for other sample cross-sections with burst modes 1, 2, 3, 4, and 5 were examined, as shown in Figure 9.  
It can be observed through the local topography that there were more un-modified areas when the number of burst modes was 1; the overall modification was the most uniform and fine when the number of burst modes was 2; when the number of burst modes was 3, due to the decrease in the energy contained in the individual pulses, there were localized un-modified areas, which were reflected in the image by the increase in the height of the highest protrusion in the modified area and the appearance of the sticky area. When the number of burst modes was 4, the sticky area of the un-modified area was further enlarged, and when the number of burst modes was 5, there were blocky areas of the unmodified area. The peak heights of the samples showed an overall increasing trend starting with burst mode 2. The roughness of the cross-section of the samples was examined by using AFM, and the results of the variation of roughness with the number of burst modes are shown in Figure 10a. The optimum results were obtained with the number of burst modes of 2, with an average roughness of 158 nm, and when the number of burst modes was increased, the roughness was also increased. At burst mode number 3, the roughness of the sample cross-section was increased slightly, but the overall modification was relatively uniform, and the roughness of different areas did not differ much. With a burst mode number of 4, areas near the incidence plane (area) had better texture modification than other areas. The  
Figure 8: Diagrams of the sample cross-section for different burst mode numbers with 1 μm spacing and 11.5 W laser incident power. (**a–e**) represent cross-sections of the samples for burst mode numbers of 1–5, respectively.