Spatial restriction on properties of nanosecond pulsed laser ablation of aluminum in water

Abstract

The evolution of plasma radiation, shock waves and the bubbles generated by laser ablation in liquids (LAL) has been investigated in spatial restriction conditions by the temporally resolved plasma radiation images and time-resolved laser shadowgraphy. No significant plasma enhancement effect is observed at the moments when two reflected waves converge in opposite directions. Two reasons may account for this phenomenon: one is that cavitation bubbles block the interaction between reflected waves and plasma, which prevents reflected waves from transmitting energy to the plasma; and the other is that the laser energy is significantly absorbed by the water medium and the emission of plasma decays rapidly in water. The results indicate that the plasma luminous intensity attenuates and lifetime decreases under restricted conditions, which is due to the existence of the moving breakdown model in the water. The Bjerknes effect of the wall on the bubbles leads to the asymmetry of the bubble evolution under restricted conditions. The dynamics of the first bubble generated by LAL is described in an analytic method with the Rayleigh–Plesset equation. The results further indicate Bjerknes force exerts little impact upon bubble evolution in the extension phase, but imposes huge effects at the shrinkage phase.