## 3 Results and Discussion
### Influence of Incident Laser Power on Cutting Results  
The incident laser power affects the intensity distribution of the Bessel beam. The effect of different laser incident powers on the machining quality was investigated in this section. The processing point spacing was 1 \(\upmu\)m, the number of burst modes was 2, and the defocus distance was adjusted to cover the whole cross-section. As shown in Figure 6a, there was ablation non-uniformity in the cross-section; when the incident energy was greater than 11.5 W, the excessive laser incident energy led to crystallization of the material in the machining region, which improved the roughness of the cross-section.  
The roughness of the sample cross-section was characterized with regard to different energies, and the results are shown in Figure 7a below.  
Figure 6: Diagrams of the samples at different laser incident powers when the processing point spacing was 1 \(\upmu\)m and the burst mode was 2. (**a–e**) represent the cross-sections at different laser incident energies, and (**f**) represents the enlarged pattern of the location of the local ablation crystals when the laser incident power was 19.01 W.  
Figure 7: (**a**) Schemes of the variation in the sample cross-section roughness with the laser incident power for a processing point spacing of 1 \(\upmu\)m and burst mode of 2. (**b**) Schemes of the variation in the breaking strength with the laser incident power for a processing point spacing of 1 \(\upmu\)m and burst mode of 2.  
The results of different power roughness detections are shown below: when the incident power was 11.5 W, the average roughness was the lowest, and the ablation was the most uniform; when the incident energy was less than this value, the ablation was not uniform and the roughness was relatively high; when the incident energy was higher than 11.5 W, the roughness of the cross-section increased further with the increase in the incident energy, and the roughness uniformity of the cross-section decreased. The standard deviation of roughness decreased when the incident energy was higher than 16 W. The average roughness of the cross-section was the lowest, and the standard deviation of roughness decreased with the increase in incident energy. Also, the standard deviation of the average roughness increased.  
This recrystallization phenomenon in regions with large Bessel beam energy distributions increased the roughness of the region. We agreed that locally changed electron densities resulting in several electrical potentials coupled with high local temperatures were the likely causes of this phenomenon. As shown in Table 3, at laser injection powers of 16.83 W and 19.01 W, the maximum difference in roughness in different regions reached 68 nm and 98.67 nm, respectively. As a result, this paper hypothesizes that with a further increase in laser injection power, the internal crystallization increases subsequently, leading to a further increase in the roughness difference between different regions.  
The breaking strength of laser incident power was characterized, and the results are shown in Figure 7b.  
As shown in Figure 7b, with a laser frequency of 100 kHz, a processing point spacing of 1 \(\upmu\)m, and a laser injection power of 8.4 W, the modification was incomplete, and the breaking strength was larger than 20 N. When the power was increased, the main flap energy of the Bessel beam was increased, and the modification area increased. When the laser injection power was 11.5 W, the modified layer completely covered the whole cross-section, and the breaking strength was significantly reduced, and when the power was further increased, the breaking strength was maintained near 10 N