LASER DRILLING INTO AN ABSORBING LIQUID

The interaction of continuous CO2 laser radiation with water is described. Tightly focused radiation at powers of up to 120 W is used to generate and maintain a conical depression in the water surface similar to the keyhole created during laser penetration welding. The observed penetration depth of up to 7 mm is explained in terms of a hydrodynamic model and observations on the interaction induced liquid flows are described. The momentum reaction to the flow of steam up out of the keyhole generates a downward flow in the liquid around the keyhole with a velocity of approximately 20 cm/s under the conditions of these experiments. The experiment has also been performed under variable gravity conditions provided by the NASA KC-135 Microgravity Aircraft to observe effects associated with changes in hydrostatic pressure and buoyancy on the system.