This topic has been mentioned in regards to digging super deep bore holes for geothermal energy. The high temps a couple miles down started to soften metal drill bits but some companies are working on lasers that are capable of melting rock to allow further digging.
An 80W CO2 LASER is plenty of power. I regularly engrave the living shit out of stone with mine, and that goes a few millimeters deep.
Get a couple kW in the same wavelength (10640nm) with a proper adjustable focus (movable diopter) and a galvo and a vacuum assist and you can just start raster-scanning your way through the rock.
