## 3 Results and Discussions
When the energy density is about 80 J/cm\({}^{2}\), the target thickness of 5 mm even needs 100 us to heat up to 3500 \({}^{\circ}\)C, while the target thickness of 1 mm only needs 70 us under the same laser conditions. This difference is determined by the thermal conductivity of the material. When the laser energy reaches the thicker material, the upper layer can better transfer the energy to the lower layer, and its thermal conductivity coefficient is much greater than that of air. The thin CFRP is more obstructed when transferring heat outward, so the heating time is shorter and the speed is faster. Figure 2: The relationship between the laser heating CFRP surface heating time and the energy density and pulse width under a single pulse. The experimental results of CFRP surface temperature with time under different laser energy density are shown in the Figure 4. It can be seen from the figure that under the condition of single pulse, when the laser energy density is different, the surface temperature of CFRP increases with the laser action time. Due to the high energy density of the laser, the surface temperature of the CFRP material rises rapidly, and the time to reach the vaporization point is only within a few microseconds. Since the strength and elastic modulus of carbon fiber materials remain basically unchanged at high temperatures above 2000 \({}^{\circ}\)C, it can be considered that the process of heating up is mostly fiber oxidation and resin decomposition. Carbon fiber will continue to absorb laser energy and then continue to heat up until it reaches the gasification point of 3500 \({}^{\circ}\)C. After the carbon fiber reaches the gasification point of 3500 \({}^{\circ}\)C, with the continuous injection of laser energy, the target surface temperature should continue to increase. However, since the upper limit of the thermometer is 3500 \({}^{\circ}\)C, the output temperature of the thermometer is always 3500 \({}^{\circ}\)C, which shows an isotherm in the Figure 4.  
When multiple pulses continuously act on the woven CFRP material, its surface temperature increases and decreases repeatedly with the laser pulse. Under the action of different energy densities, the temperature drop rate and fall value are different at the end of each pulse. The greater the energy density, the slower the temperature decline rate, and the fall temperature measured in the experiment shows that it has a significant temperature  
Figure 4: Under the condition of single pulse, the surface temperature of laser damaged CFRP changes with time. (d = 1 mm, \(\tau_{\text{p}}\) = 1 ms). Figure 3: The relationship between the temperature rise, time of laser irradiate CFRP surface, and the thickness of the material under the experimental condition of single pulse (\(\tau_{\text{p}}\) = 1 ms). accumulation effect. In the experiment, five laser pulses were used to irradiate the CFRP target with a braided structure. The pulse width was 1 ms, the repetition frequency was 10 Hz, and the laser output energy was adjusted (152-699 J/cm\({}^{2}\)) to obtain the end of each pulse and the target at the time of the next pulse. The temperature of the surface is the initial temperature at which each pulse acts on the target starting from the second pulse. As shown in Figure 5, under the action of lasers with different energy densities, the temperature drop of the material after each pulse is different. After the end of the first pulse, under five different laser injection energies, there was no temperature accumulation higher than 350 \({}^{\circ}\)C. When the energy density is 392 J/cm\({}^{2}\) and 699 J/cm\({}^{2}\), after the end of the second pulse, the temperature will obviously accumulate when the third pulse arrives; when 241 J/cm\({}^{2}\) and 152 J/cm\({}^{2}\), they are in the third and fourth After the end of each pulse, the temperature drops back above the initial temperature.