This video presents two "identical" experiments with the same laser-matter interaction and however produce two opposite jetting conditions. A NdYAG pulsed laser (4 GW/cm², 10 ns, 1064 nm) is striking the bottom face of the aluminium bottom of a liquid filled tank. The laser-matter interaction occurs in water confined regime. The shock wave hence generated travels through the aluminium layer and breaks out into the liquid. At the bottom-liquid interface, a bubble is bulging and then collapsing. During the collapse, two behaviours were observed : 1) when the bubble's contact angle was superior to 90°, the collapse comes up by the bottom wall and makes the jet going upward, resulting to a jet going out of the tank ; 2) when the bubble's contact angle is lower than 90°, the bubble collapse comes from the top of the bubble and strikes the bottom wall. We could evidence it by a numerical approach performed at Institut Jean Le Rond d'Alembert. We met this funny situation by neglecting replacing the bottom aluminium plate at every shot : after one shot the plate exhibitted a platic deformation that changed the contact angle to a lower value, modifing the jetting condition.
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11 окт 2022
