## 3 Results and Discussion
### Influence of Incident Laser Power on the Cutting Effect  
When the incident laser power changes, the intensity distribution of the Bessel beam will also be affected. As shown in Figure 7, when the processing point spacing is 1 \(\upmu\)m and the number of burst modes is 2, the defocusing distance is adjusted so that the focal depth covers the entire section. When the incident laser power is too high, such as greater than 12.5 W, the Bessel beam may cause excessive crystallization of the material during sample processing. This excessive crystallization cannot improve the machining quality but may lead to increased section roughness. The roughness of the sample section under different energies was characterized, and the results are shown in Figure 8a below. The test results of different power roughness are as follows: when the incident power is 12.5 W, the average roughness is the lowest and the ablation is the most uniform; when the incident energy is less than this value, the ablation is not uniform, and the focal depth of the Bezier beam cannot cover the whole section, resulting in high roughness; when the incident energy is greater than 12.5 W, with  
Figure 6: **(a)** Local AFM topography of the sample section under different pulse numbers when the processing point spacing is 1 \(\upmu\)m and the laser incident power is 12.5 W. **(b)** Fracture strength diagram under different pulse numbers when the processing point spacing is 1 \(\upmu\)m and the laser incident power is 12.5 W.  
Figure 7: Schematic diagram of the sample under different laser incident power when the processing point spacing is 1 \(\upmu\)m and the burst mode is 2. **(a–e)** is the cross section under different laser incident energies, and **(f)** is the enlarged image of the local ablative crystal position when the laser incident power is 20 W.  
the increase in the incident energy, the section roughness further increases, and the section roughness uniformity decreases; and when the incident energy is greater than 15 W, the standard deviation of roughness decreases. The average roughness of the section is the lowest, and the standard deviation of the roughness decreases with the increase in the incident energy, and the standard deviation of the average roughness also increases. This recrystallization phenomenon increases the roughness in the region where the Bezier beam energy distribution is large. In this paper, it is suggested that the local electron density changes lead to several potential changes, and the local high temperature leads to this phenomenon. As shown in Table 3, when the laser injection power is 17.5 W and 20 W, the maximum roughness difference in different regions reaches 202.05 nm and 373.3 nm, respectively. Therefore, it is assumed that with the further increase in the laser injection power, the internal crystallization will increase, resulting in a further increase in the roughness difference between different regions. The fracture strength of laser incident power is characterized by the average roughness of the cross section and the maximum difference in each region under different incident powers in Table 3. The results are shown in Figure 8b. In Figure 8b, when the laser frequency is set to 100 kHz, the processing point spacing is 1 \(\upmu\)m, and the laser injection power is 7.5 W; it is observed that the modification effect is incomplete and the breaking strength is greater than 20 N. With the increase in laser power, the energy of the Bessel beam increases correspondingly, and it can cover a larger modified area. When the laser injection power reaches 12.5 W, the modified layer completely covers the whole section, and the fracture strength decreases significantly. After the laser injection power is further increased, the fracture strength is stable at about 2 N, which shows the effect of high power on the modification effect. Figure 8: **(a)** Sample section roughness variation with laser incident power when the processing point spacing is 1 \(\upmu\)m and the burst mode is 2.