## 3 Results and Discussions
Under the action of a laser with a fixed pulse frequency, the higher the energy density, the more obvious the temperature accumulation is and the higher the fall temperature. When the laser energy density is constant, the fallback temperature increases as the number of pulses increases. Figure 6 shows the differences between various samples. The morphology illustrated that elliptical surface structures although the laser beam spot is a circle. Similar to the results by simulation, the axis of the ellipse is precisely as the axis of the carbon fiber. From the top view, the elliptical performance is clearer, when the laser beam irradiates just right on the cross-section of fibers. Moreover, due to the braided structure, the position of the laser beam on these samples are all at the upper fibers. At the same time, all long axes of ellipses are corresponding to these upper fibers. The bottom row shows the right view of the samples' morphology focusing on debris. It is clear that all sample appear debris at the top surface around the hole. The highlight is the variety of debris size in the horizontal and vertical axes. The debris is only gathered in the long axis of the ellipse and is less in the short axis, which is either due to the magnetizable effect or is related to the formed pattern of the carbon fiber. Figure 5: Under the condition of multi-pulse laser, the temperature rise time of laser damaged CFRP (braided) surface changes with the pulse number. Furthermore, the shape of the ablation hole under the surface is regular cone but not an elliptic cone. The elliptical phenomenon only appears on the material surface. When the prepreg material formed to a carbon fiber plate, the blank between the fibers in adjacent layers is filled by epoxy. However, the epoxy will be removed at the initial moment of laser processing, and the heat in z direction will hardly transfer into the next layer especially via the air. In order to further analyze the anisotropy of heat conduction in CFRP, it can be discussed from a microscopic perspective. The heat transfer of metal material depends on the lattice thermal vibration wave and free electron flow. Therefore, the heat transfer of metal materials mainly depends on free electrons. However, the heat transfer of non-metallic materials mainly depends on lattice vibration, which does not follow the Weideman-Franz law. Carbon fiber belongs to this type of non-metallic materials. The atoms at a high temperature have a larger amplitude, and those at a low temperature have a smaller amplitude. The heat energy is transferred gradually from high to low in order to balance the temperature. Therefore, the phenomenon is attributable to the differences among the three directions of fibers. Figure 7 is a schematic of the thermal vibrations of the lattice. The vibration of atoms in the lattice at a certain temperature has a corresponding amplitude (displacement). The atoms at a high temperature have a larger amplitude, and those at a low temperature have a smaller amplitude. The heat energy is transferred gradually from high to low in order to balance the temperature. Therefore, the phenomenon is attributable to the differences among the three directions of fibers. Figure 6: Morphology of CFRP measured by a 3D surface measuring instrument. Sample (**A**) N = 1, I = 990 J/cm\({}^{2}\), \(\tau_{\rm p}\) = 1 ms; Sample (**B**) N = 5, I = 103 J/cm\({}^{2}\), \(\tau_{\rm p}\) = 1 ms; Sample (**C**) N = 10, I = 149 J/cm\({}^{2}\), \(\tau_{\rm p}\) = 1 ms.  
Figure 7: Schematic of the thermal vibrations of a lattice (plaid dot, the position of the atom before the vibration; filled dot, the position of the atom after the vibration). Moreover, the property of CFRP composite is sensitive to particular laser condition. When the laser irradiates on carbon fibers, due to the organized oscillations of lattice vibration of material, the fiber would crack and burst apart in the horizontal direction.