Anomalous Behavior of Cavitation Bubbles Observed in Pulsed Laser Ablation of Ni in Liquid CO2 near the Critical Point

Pulsed laser ablation of Ni targets in liquid CO₂ near the critical point (C.P.) (P_crit = 7.38 MPa, T_crit = 304.1 K) was performed and the time evolution of the plasma and the ensuing cavitation bubble analyzed by shadowgraph imaging. Formation of double-layered anomalous cavitation bubbles was observed inside the liquid phase close to the C.P. The size and propagation speed of the cavitation bubbles were measured and it was found that in the experimental range investigated (P = 7.20-7.40 MPa, T = 301-303 K), the size of the cavitation bubble increased by a factor of up to three for increasing pressure and temperature, whereas the propagation speed decreased.