We applied external high pressure to ambient water in liquid-phase laser ablation. As a result, it was found that the maximum volume V max of a cavitation bubble induced by laser ablation satisfied a scaling law of V max / P À1 ext with P ext being the pressure applied to water. The effect of the pressurization was also observed in the shape of the second bubble induced by the collapse of the first cavitation bubble. These experimental results indicate that the dynamics of a cavitation bubble induced by liquid-phase laser ablation is controlled by the external pressure. #

We applied laser-light scattering for investigating the growth processes of nanoparticles in liquid-phase laser ablation. We observed the growth of nanoparticles inside the cavitation bubble. This means that particles ejected from the target are transported into the cavitation bubble, and they condense into nanoparticles inside it. The production of nanoparticles was efficient until 3 s after the irradiation of the laser pulse for ablation, indicating the fast growth of nanoparticles. A part of nanoparticles was transported from the cavitation bubble toward the water, but the great portion of nanoparticles was stored in the cavitation bubble until the collapse.

The solution of the conventional Rayleigh–Plesset equation did not agree with the experimental results on the temporal variations of the sizes of cavitation bubbles produced by laser ablation in water. In this work, we modified the conventional Rayleigh–Plesset theory in the following two points to reproduce the experimental observation theoretically. One was to introduce the effect of the contact angle among the water, the cavitation bubble, and the ablation target. The other was to treat the surface tension and the kinematic viscosity coefficient of water as additional adjusting parameters to fit the theoretical result with the experimental observation. The latter modification was effective especially for laser ablation in the pressurized water. Better agreement between the theoretical and the experimental results was realized with the help of these modifications, but anomalous thermodynamic parameters were necessary to obtain the best fitting. We evaluated the pressures and the temperatures inside the cavitation bubbles.

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