# Laser Irradiation on Limestone and Cracking: An Experimental Approach
## 3 Results
### Analysis of Hole Size  
Figure 5a shows the changing trend of the hole diameter of the dried sample with the increase in irradiation time. The hole diameter increases from 2.25 mm to 2.70 mm with increasing irradiation time when the specimen is irradiated at a power of 90 W. The hole diameter increases from 2.73 mm to 2.98 mm with increasing irradiation time when the specimen is irradiated at a power of 135 W. Figure 5b shows the trend of hole diameter of the soaked sample with increasing irradiation time. The hole diameter increases from 1.95 mm to 2.39 mm with increasing irradiation time when the specimen is irradiated at a power of 90 W. The hole diameter increases from 2.65 mm to 3.07 mm with increasing irradiation time when the specimen is irradiated at a power of 135 W. It can be seen that the hole diameter of the specimen tends to increase with increasing irradiation time and power. In addition, the hole diameter value of the soaked specimen is smaller than the hole diameter of the dried specimen.  
Figure 4: Variation of high temperature area with irradiation time.  
Figure 6a shows the changing trend of the hole depth of the dried sample with the increase in irradiation time. The hole depth increases from 2.68 mm to 4.02 mm with the increase in irradiation time when the specimen is irradiated at a power of 90 W. The hole depth increases from 7.20 mm to 9.21 mm with increasing irradiation time when the specimen is irradiated at a power of 135 W. Figure 6b shows the trend of hole depth of the soaked sample with increasing irradiation time. The hole depth increases from 2.90 mm to 3.02 mm with the increase in irradiation time when the specimen is irradiated at a power of 90 W. The hole depth increases from 3.88 mm to 5.02 mm with increasing irradiation time when the specimen is irradiated at a power of 135 W. It can be found that the reduction in hole depth of the soaked sample is 15% at a power of 90 W and 45% at a power of 135 W compared with that of the dried sample.  
Comparing Figure 5 with Figure 6, it can be found that increasing the laser power has a significant effect on the hole depth. This is because when the laser beam melts the rock and forms a hole, it loses direct contact with the surrounding solid rock, impeding the transfer of energy to the immediate vicinity, while maintaining a constant input of energy to the rock directly below. In addition, limestone is composed mainly of calcium carbonate, which is dense in composition. Calcium carbonate has a high melting point of 1340 \({}^{\circ}\)C but decomposes into calcium oxide and carbon dioxide at around 850 \({}^{\circ}\)C. The decomposition of calcium carbonate consumes a lot of energy and prevents the temperature of the nearby rocks from rising. Figure 7 shows the typical morphology of limestone pores after laser  
Figure 5: Variation of hole diameter with irradiation time under different conditions (**a**) dried sample; (**b**) soaked sample.  
Figure 6: Variation of hole depth with irradiation time under different conditions (**a**) dried sample; (**b**) soaked sample.  
irradiation. The presence of water reduces the hole diameter and depth and can increase the cost of drilling. In addition, water is involved in the chemical reaction of calcium carbonate at high temperatures.