## 4 Results and Discussions
### Influence of Different Laser Pulse Energy on Ablation Depth  
The evolutions of maximum temperature under different laser pulse energies were investigated in this paper by numerical simulation. The results are shown in Figure 7. These temperature variations share a similar trend: An extreme temperature value is reached  
Figure 6: The morphology of single-dot experiment with LWJ. during the laser pulse duration, then the surface layer which exceeds the melting point is peeled by the water jet. Hence, the laser heat flux will be applied to the remaining material. In this stage, a weak balance of surface temperature is achieved by the combined effect of laser and water jet until the end of the pulse duration. Then, a sharp drop in temperature arises whereafter a gradually slow trend begins throughout the rest of one 1/f period. The different maximum temperatures are listed in Figure 7 with the insertion of a red line at the same location (2973.15 K). According to the theory of LWJ machining, the CMCs material removal can only occur in the area above the red line. Obviously, a stronger processing capability could be obtained under a higher laser pulse energy. To achieve a more reliable numerical result, the processing capabilities of each individual pulse energy were calculated. Figure 8 reveals the cross-section status of the CMCs model after the treatment of LWJ. As demonstrated in Figure 8a, the material of the top surface is peeled with a smooth transition at the edge. The diameter of the overall area is approximately 55 \(\upmu\)m with a 50 \(\upmu\)m size of the central flat zone. The substrate status at 1.38 \(\times\) 10\({}^{-6}\)s (\(t\) = 16 \(\times\) tp) is shown in Figure 8b. Corresponding to Figure 5g, an annular distribution of high temperature with 1855 K is obtained, which spreads downward to 3 \(\upmu\)m on the \(z\)-axis. This result indicates that thermal diffusion could be effectively restricted using the method of LWJ. In the last time step of one 1/f period, the substrate temperature is minimized by the heat convection of water and air, as shown in Figure 8c. An annular distribution of temperature similar to Figure 8b is still presented with a diffusion distance of 5-10 \(\upmu\)m. However, the maximum temperature is only 494.5 K, which is far below the thermal damage threshold of CMCs and hardly affects the SiC fibers. The central flat zone  
Figure 7: Evolution of maximum temperature of CMCs surface in different laser pulse energies: (a) 0.4 mj; (b) 0.6 mj; (c) 0.8 mj; (d) 1 mj. was adopted as a judgment criterion to evaluate the material removal, a depth of 0.853 \(\upmu\)m could be achieved by means of measuring the coordinates. Furthermore, from Figure 7, it was discovered that the difference among maximum temperatures is able to reach more than 1200 K. The differentiated temperature fields are reflected in the efficiency of material removal. Figure 9 displays the numerical results of CMCs material removal in different laser pulse energies. The ablation depths with 0.4 mJ, 0.6 mJ, 0.8 mJ and 1 mJ are 0.267 \(\upmu\)m, 0.371 \(\upmu\)m, 0.559 \(\upmu\)m, and 0.853 \(\upmu\)m, respectively. On the basis of this type of theoretical calculation, one assumption is put forward. In the case of 1 mJ pulse energy and 50 KHz repetition frequency, a micro-hole with a significant machining depth of 41.65 mm and a diameter of 55 \(\upmu\)m would be acquired in 1 s. Even though this result occurs in an ideal situation, this finding is somewhat counterintuitive and has few possibilities in the actual experiment. Figure 8: Status analysis of material removal with LWJ at **(a)**\(t\) = 4.3 \(\times\) 10\({}^{-8}\) s; **(b)**\(t\) = 1.38 \(\times\) 10\({}^{-6}\) s; **(c)**\(t\) = 1.99 \(\times\) 10\({}^{-5}\) s.  
Figure 9: Numerical results of CMCs material removal in different laser pulse energies. For this numerical result, there are some possible explanations.