Characteristics of optical emission intensities and bubblelike phenomena induced by laser ablation in supercritical fluids

We investigated the characteristics of laser ablation phenomena in supercritical fluids by optical emission and shadowgraph imaging. In comparison with laser ablation in liquid H₂O, the optical emission of a laser ablation plasma produced in supercritical H₂O had a longer lifetime and a larger transport length. It was found in supercritical CO₂ that laser ablation plasmas with bright optical emissions were produced at a mass density of approximately 300 kg/m3. A clear correlation between the optical emission intensity and the density fluctuation was not observed in our experimental results, which were obtained in a regime deviated from the critical point. Bubblelike hollows were observed by shadowgraph imaging in both supercritical H₂O and CO₂. The dynamics of the bubblelike hollows were different from the dynamics of a cavitation bubble induced by laser ablation in a liquid medium but relatively similar to the dynamics of ambient gas in gas-phase laser ablation.