Transient interaction of a boiling melt with a pulsed Nd:YAG-laser

• A special interaction between pulsed Nd:YAG-laser and boiling melt was studied.
• The interaction zone was observed and analysis based upon high speed imaging.
• Switching to pulse low enable surface tension to drag the melt back toward the top.
• pulse high drilling a hole through bulk of melt to developed later a cut instead.
• pulse low smoothing the front waves and generate semi-torus-like Catanoid shape.

The boiling front induced by a pulsed Nd:YAG-laser at very slow translation speed was studied. The purpose is to understand fundamental melt movement mechanisms. The melt was observed by high speed imaging, with and without illumination. When switching on the laser beam a hole is drilled through a bulk of melt. The hole expands and the boiling pressure gradually opens the melt bridge, instead developing an interaction front similar to cutting. These conditions remain in quasi-steady state during the pulse. The ablation pressure from boiling shears waves down the front and keeps the melt downwards in a stable position. When switching off, the waves smoothen and in absence of boiling the surface tension drags the melt back upwards, to semi-torus-like Catenoid shape. Evidence on the large melt pool and its shape was achieved by three-dimensional reconstruction from cross section macrographs. The basic findings how melt can move with and without ablation pressure can enable controlled melt dynamics for various laser processing techniques, like remote cutting, ablation, keyhole welding or drilling.