# Experimental Study on Femtosecond Laser Processing Performance of Single-Crystal Silicon Carbide
## 3 Results and Discussions
### Experimental Results  
#### 3.2.1 Analysis of Single Factor Experimental Results  
Figure 3 shows the fluence distribution of Gaussian beam. The spatial distribution of Gaussian beam shows that the energy is mainly concentrated in the center of the laser spot, so only the energy at the center of the spot is greater than the ablation threshold energy. As the laser fluence increases, the central radius of the spot area with energy greater than the ablation threshold increases. The distribution of laser fluence in the direction of spot radius is [9]:  
\[F(r)=F_{max}e^{-\frac{2r^{2}}{\omega_{0}^{2}}} \tag{1}\]  
where \(F_{max}\). is the peak fluence, \(r\) is the radial size, and \(\omega_{0}\) is the waist radius. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Variable** & **Depth (\(\mu\)m)** & **Width (\(\mu\)m)** & **MRR (\(\mu\)m\({}^{3}\)/s)** & **HAZ (\(\mu\)m)** & \(\Theta\) (\({}^{\circ}\)) \\ \hline Fluence (J/cm\({}^{2}\)) & *** & *** & *** & *** & *** \\ Scan speed (\(\mu\)m/s) & *** & *** & - & *** & *** \\ Repetition rate (Hz) & *** & ** & *** & *** & *** \\ Multi-scanning & *** & ** & *** & *** & *** \\ NA & *** & *** & *** & *** & *** \\ \hline \end{tabular}  
* insignificant \(p\) \(>\) 0.1.  
\end{table} 
Table 2: Significance analysis of the effect of process parameters on the morphology of grooves. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Variable** & **Depth (\(\mu\)m)** & **Width (\(\mu\)m)** & **Aspect Ratio** & **MRR (\(\mu\)m\({}^{3}\)/s)** & **HAZ (\(\mu\)m)** \\ \hline Fluence (J/cm\({}^{2}\)) & *** & *** & *** & *** & *** \\ Scan speed (\(\mu\)m/s) & *** & *** & *** & *** & *** \\ Multipass scanning & *** & *** & *** & *** & *** \\ Polarization angle (\({}^{\circ}\)) & - & - & - & - & *** \\ z-layer feed (\(\mu\)m) & *** & *** & *** & *** & *** \\ \hline \end{tabular}  
* insignificant \(p\) \(>\) 0.1.  
\end{table} 
Table 3: Significance analysis of process parameters on processing characteristics. From Equation (1), it can be seen that in the direction of laser radius, the laser fluence decreases exponentially with the increase in radius. As the peak fluence increases, more energy is injected into the workpiece in the laser propagation direction, and the change in the depth direction of the groove is more significant than the change in the width direction of the groove. Figure 4 shows the effect of fluence on the size of groove, MRR, HAZ and side wall inclination angle. As shown in Figure 4a, as the fluence increases, the temperature and carrier density in the conduction band increase, thereby increasing light absorption [23]. The more energy is deposited in the material and the groove is wider and deeper. As shown in Figure 4b, the MRR increases with the increase in laser fluence. Due to the high laser fluence allowing more energy to be input into the material at a constant scan speed and pulse repetition rate, the depth and width of the groove increase, resulting in an increase in the cross-sectional area of the groove. It can be seen from Figure 4c that with the increase in laser fluence, the laser cladding layer increases and the HAZ increases. The recoil force is the main reason for the irregular edges of redeposition and recasting humps [24]. As shown in Figure 4d, as the laser fluence increases, material removal increases, the inclination angle of the sidewall increases and the grooves become steeper. Figure 4: _Cont._  
Figure 3: Fluence distribution of Gaussian beam (\(F_{1}>F_{2}\)). Figure 5 shows the effect of scan speed on the size of groove, MRR, HAZ and side wall inclination angle. With the increase in laser scan speed, the laser energy received by SiC in unit time decreases and the width, depth, side wall inclination angle and HAZ of the groove gradually decrease.