Experimental Evaluation of Rock Spallation with Laser Irradiation

When lasers were invented in 1960, they were called “a solution looking for a problem.” Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, medicine, industry, entertainment and the military. Research conducted in rock destruction by high-power lasers indicates that lasers can be a less expensive, environmental friendly alternative to conventional drilling and perforating methods. Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper.