Underwater rock drilling by CO₂ laser

As part of a fundamental study of rock drilling by laser irradiation, this paper describes the evolution of a cavitation cone created by pulsed CO2 (carbon dioxide) laser irradiation in water. A granite specimen submerged 50mm below the water surface was intermittently irradiated by a CO2 laser beam. High-speed video observations revealed the generation of an initial cone-shaped water cavity, propagation of the laser beam through the cavity and eventual ablation of the granite surface. The laser beam locally melts the granite surface to form small glassy beads, which are readily removable by mechanical methods. Repetition of this procedure demonstrated that a high-power laser beam propagating in water can be used to create a hole in rocks. This paper reports on the observed process by which molten granite is formed into small glass particles in the water.