# Laser Irradiation on Limestone and Cracking: An Experimental Approach
###### Abstract  
Using mechanical drilling to obtain energy resources stored in deep and hard rock layers is becoming increasingly challenging. Therefore, laser irradiation has emerged as a new and promising drilling method. In this study, the effects of immersion conditions on rock-breaking by laser irradiation on the temperature, hole size, rock-breaking efficiency, and macro-fracture after laser irradiation were investigated. Furthermore, the mineral changes and thermogravimetric analysis of rocks were studied. As indicated by the results, the temperature area over 100 \({}^{\circ}\)C increases with the increase of irradiation time, and the temperature range of between 2.27 cm\({}^{2}\) and 13.20 cm\({}^{2}\) varies with the change of laser power at between 90 W and 135 W. The hole-diameter value of the soaked sample was smaller than that of the dried sample. In addition, the hole depth of the soaked sample reduced by 15% at a power of 90 W and 45% at a power of 135 W, compared with that of the dried sample. The value of the modified specific energy of the soaked sample increased, which was particularly noticeable at low power. The soaked sample had a larger effect on the rate of perforation at high power and a smaller effect at low power. The cracks on the surface of the rock samples became larger after being placed for one month. Fracture length increased from 0.61 to 5.09 mm for dried samples and from 2.24 to 8.7 mm for soaked samples at a laser power of 90 W. Fracture length increased from 6.30 to 9.85 mm for dried samples and from 9.04 to 11.38 mm for soaked samples at a laser power of 135 W. The soaked sample began to show differences when heated at 100 \({}^{\circ}\)C, which was caused by the evaporation of some free water molecules in the rock. The main weight loss temperatures of the samples occurred in the range of 640 \({}^{\circ}\)C to 900 \({}^{\circ}\)C.  
laser irradiation; surface morphology; soaked rock; thermograv +
Footnote †: journal: Applied Sciences
Research on the laser irradiation of rocks started in the 1960s, and can be broadly divided by research into two stages, including the rock-cutting stage of the low-power laser before 1994 and the drilling and rock-breaking stage of the high-power laser after 1994 [19]. In 1968, [PERSON] et al. [20] of the Massachusetts Institute of Technology proposed the idea of using the laser to break rock and drill at the 43 rd SPE/AIME autumn annual meeting. This was the first time that laser rock-breaking had been formally proposed. The Lebedev Institute of Physics, the military laser research center of the Soviet Union, followed closely and carried out research, achieving results on the irradiation of rocks with kilowatt-level lasers from 1968 to 1978 [21]. [PERSON] et al. [22] compared laser drilling with other drilling techniques and investigated the effect of lasers on 13 different rock types. [PERSON] et al. [21] carried out the feasibility experiment of laser irradiation on rock, which proved that rock-breaking by laser irradiation is superior to mechanical drilling in efficiency. [PERSON] et al. [23] studied the interaction between high-power lasers and rock and the effect of lasers on rock porosity, permeability, strength, and other properties, and pointed out the application advantages of lasers in the oil and gas industry. [PERSON] et al. [24] used a 1.6 kW laser to irradiate dry sandstone and water-saturated sandstone. The results of the study indicated that the existence of water would make the experimental effect change more obviously. [PERSON] et al. [25] examined the influence of different parameters on rock-breaking by laser irradiation through laboratory experiments. [PERSON] et al. [26] conducted field experiments with laser techniques and showed that lasers could improve the permeability of the hole and its surrounding rock matrix, making it easier for oil and gas to enter the hole. [PERSON] and [PERSON] et al.