Energy efficiency of drilling granite and travertine with a CO2 laser and 980 nm diode laser

Using lasers to drill hard rock presents potential advantages compared to conventional mechanical drilling, such as higher penetration rates and reduced vibration. Before realistic drilling tools can be proposed, the influence of important parameters and the mechanisms involved in drilling different rocks with different lasers must be understood. In this work, we investigate the efficiency of laser drilling of granite and travertine with a CO₂ laser and a 980 nm fiber coupled diode laser. At the drilling surface, the maximum CW power delivered by the CO₂ laser was 140 W, while the diode laser delivered up to 215 W. Even at these modest power levels, it was possible to drill holes with diameters of the order of 8 mm at efficiencies varying from 40 kJ/cm³ to 150 kJ/cm³. The optimum laser exposure period of time was also investigated. Finally, x-ray diffraction and fluorescence analysis, as well as Tg (Thermogravimetry) and DTA (Differential Thermal Analysis) measurements, were performed on the rocks samples used.