Abnormal Phenomenon of Laser-Drilling a Plate Underwater

The efficiency of laser-drilling a metal plate in water was observed higher than that in air. A new mechanical sensor based on optical deflection technique was applied to investigate the force acting on a metal in water and air respectively during laser-matter interaction. It is shown that in air the sample is only affected by laser-induced ablation, while underwater it is impacted not only ablation, but also two liquid-jet impulses. Both the amplitude and duration of three forces underwater are much larger than those in air. By scanning electronic microscope, the shape of laser-drilling holes is observed and their different mechanisms in water and air are analyzed in detail.