Study of liquid and vapor ejection processes during laser drilling of metals

In an experimental investigation of laser–metal interaction, one of the important parameters is the propagation velocity of the liquid–vapor interface. The quantity appears as a direct result of the theoretical examination of the interaction and may be used to test the accuracy of the theory. Consequently, in the present study, the nature of the interaction mechanism between a pulsed laser beam and metals is examined using streak photographs of the ejecta from four metals: titanium, tantalum, nickel, and EN58B stainless steel. It appears that the drilling process commences with evaporation and the expulsion of fairly large liquid particles, followed by further liquid ejection by both radial flow and nucleation-induced explosions, with a reduction in the quantity of vapor ejected.