## 3 Results and Discussion
### Influence of Pulse Energy on CVD Diamond Coating Ablation  
SEM photographs of the diamond coating surface irradiated under different pulse energies at the scanning speed of 1 mm/s and repetition rate of 1 kHz are displayed in Figure 5. It can be found that the variation of pulse energies has a considerable influence on the morphology of the diamond  
Figure 4: Raman spectra of the diamond coatings irradiated under different scanning speeds. (**a**) As-grown, (**b**) 2.0 mm/s, (**c**) 1.8 mm/s, (**d**) 1.6 mm/s, (**e**) 1.4 mm/s, and (f)1.2 mm/s. Figure 3: White light (WL) interferometer reconstructed results of fs laser-irradiated regions under different scanning speeds. (**a**) 2.0 mm/s, (**b**) 1.8 mm/s, (**c**) 1.6 mm/s, (**d**) 1.4 mm/s, (**e**) 1.2 mm/s, and (**f**) the surface roughness Ra and removal rate per laser pulse of diamond coating vs. scanning speed. coatings. When the pulse energy is low, the accumulated energy in the irradiated region is not enough to evaporate the materials but only to melt them. With the shifting of the laser spot, the melting materials re-solidified on the surface of the coating and compacted the arrangement of the laser-induced periodic structures owing to the abrupt temperature dropping, and the irradiated region showed a homogeneous morphology (see Figure 5a). When pulse energy rose to 80 \(\upmu\)J or higher, the morphology of the coating changed dramatically, displaying a loose periodic structure with a large number of melting slags adhering to them. In this stage, the ablation of the diamond coating combined with melting and vaporization. The melted materials could not re-solidify on the coating surface. Instead, they are vaporized by the intensive fs pulses. The three-dimensional topographies of the diamond coatings produced under the given conditions are presented in Figure 6. It can be observed from the y profile of the coating surface that the depth of the irradiated region increased as the pulse energy rise from 50 \(\upmu\)J to 100 \(\upmu\)J. The surface roughness Ra and MRR are plotted against pulse energies in Figure 7. The tendency of the surface roughness is consistent with the variation of the x profile obtained along the irradiated grooves (see Figure 6). A strong dependency of Ra on MRR was observed under the given condition that the higher the MRR, the greater the Ra. The dependency of Ra on MRR observed in this part is in good agreement with the conclusion proposed by [PERSON] et al. [30]. It is easy to understand that when adopting high-energy to irradiate the target, the interaction between laser and target becomes more intensive, thus causing the surface smoothness to worsen. The integrated deconvolution fitted Raman spectra of the diamond coating surfaces irradiated under different laser pulse energies are shown in Figure 8. As expected, increasing pulse energies is severely detrimental to the content of diamond. With the rise of the pulse energies, the diamond peak disappears finally. Again, consistent with the results discussed in Section 3.1, the compressive stress in the diamond coatings can be released by ablation enhancement. The Raman spectrum at 80 \(\upmu\)J shows a similar characteristic to the Raman spectrum at 1.2 mm/s in Figure 4f, suggesting the degree of ablation under the two processing conditions is close to each other, while the surface roughness under the two conditions also proves this point. Moreover, the relative intensity of D peaks increases significantly as  
Figure 5: SEM photographs of fs laser-irradiated regions under different single pulse energies. (**a**) 50 \(\upmu\)J, (**b**) 70 \(\upmu\)J, (**c**) 80 \(\upmu\)J, and (**d**) 100 \(\upmu\)J. The red arrow indicates the direction of laser polarization. pulse energy rises, which indicates a growth of sp2 hybridized carbon phases and serious dislocations in the diamond lattice. Figure 6: WL interferometer reconstructed results of fs laser-irradiated regions under different pulse energy.