# Laser Irradiation on Limestone and Cracking: An Experimental Approach
## 3 Results
### Micro-Fractures after Laser Irradiation  
Figure 9 shows the images of the surface of the dried sample after irradiation with the power of 90 W for 90 s, 120 s, 150 s, and 180 s (corresponding rock numbers are #1, #2, #3, and #4 respectively). It can be seen from Figure 9e-h that after the limestone is placed for one month, its cracks develop more obviously. Sample 1 has two outwardly extending cracks near the small hole, but not through the specimen. Sample 2 has one crack radiating outward to the edge of the rock surface. Sample 3 has two cracks extending to the edge of the rock surface, and the two cracks are in the same direction. Sample 4 has two cracks running through the rock surface, one of which turns at the edge. The cracks are developed after the specimens have been left for a while, and the cracks are more complex in specimens with long irradiation times. Figure 8: Plots of (**a**) modified specific energy versus irradiation time; (**b**) rate of perforation versus irradiation time. Figure 9: Surface morphology of dried sample after laser irradiation at a power of 90 W (**a**) 90 s; (**b**) 120 s; (**c**) 150 s; (**d**) 180 s; (**e**) 90 s after one month; (**f**) 120 s after one month; (**g**) 150 s after one month; (**h**) 180 s after one month. Figure 10 shows the images of the surface of the soaked sample after irradiation with the power of 90 W for 90 s, 120 s, 150 s, and 180 s (corresponding rock numbers are #9, #10, #11, and #12 respectively). It can be seen from Figure 10e-h that after the limestone is placed for one month, its cracks develop more obviously. Sample 9 has a fracture extending to the edge of the rock surface. Sample 10 has two fine cracks extending outward. Sample 11 has three cracks expanding to the edges and the cracks become curved. Sample 12 has four cracks running through the surface of the rock and the degree of curvature of the cracks has increased significantly. The later crack development of the soaked sample is significantly better than that of the dried sample, indicating that the soaked samples have advantages in the later-stage crack growth after laser irradiation. Figure 11 shows the images of the surface of the dried sample after irradiation with the power of 135 W for 90 s, 120 s, 150 s, and 180 s (corresponding rock numbers are #5, #6, #7, and #8 respectively). It can be seen from Figure 11e-h that after the limestone is placed for one month, its cracks develop more obviously. Sample 5 has three fine cracks extending outward. Sample 6 has three cracks radiating outward to the edge of the rock, and a connecting crack connecting two of them. Sample 8 has four cracks extending to the edge of the rock. The cracks on the surface of the samples all develop greatly, resulting in part of the rock samples on the surface detaching or even cracking as a whole, and new cracks appear in some samples. Figure 12 shows the images of the surface of the soaked sample after irradiation with the power of 135 W for 90 s, 120 s, 150 s, and 180 s (corresponding rock numbers are #13, #14, #15, and #16 respectively). It can be seen from Figure 12e-h that after the limestone is placed for one month, its cracks develop more obviously. Sample 13 has four fine cracks extending outward. Sample 14 has four cracks radiating outwards to the edge of the rock surface. Sample 15 has four cracks extending to the edge of the rock and a connecting crack connecting two of them. Sample 16 has four cracks extending to the edge of the rock, and one of the cracks has a branch crack, which increases the complexity of the cracks on the rock surface. In addition, it can be found that the crack opening increases with the increase of irradiation time. This is because the limestone composition is dense, and it is difficult to form cracks when the shape is complete.