Bubble Generation in Fluid Containing Gold Nanoparticles by Laser Irradiation. (1) Time-resolved visualization

Gold nanoparticles cause "localized surface plasmon resonance" for electromagnetic waves with a specific wavelength. The electrons cause resonant absorption and can be heated efficiently due to electron-phonon interaction. In particular, bubbles will be generated around them when irradiated by a strong enough laser in a liquid environment. The bubbles are known as "plasmonic bubbles." These phenomena are expected to be applied in various fields, such as medical and energy engineering. However, the mechanism of it is not yet fully understood. Therefore, we observed these generated bubbles individually at 900 kfps with a high-speed camera in this study. It was found that the bubbles exhibit complex behaviors, such as collapsing while oscillating their diameters. With the image processing technique, the time dependence of the bubble diameter was analyzed. We have shown that the generated bubbles collapse through two processes. The former is the steam condensation with a collapsing time scale of a few to several tens of microseconds. The latter is the re-dissolution of dissolved air with a collapsing time scale of hundreds to thousands of microseconds.