High-speed fluid phenomena caused by laser beam focusing in liquid nitrogen

The high-speed phenomena caused by the focusing of a pulsed laser beam in liquid nitrogen is studied experimentally with an image converter camera. The focusing of a laser beam elevates the energy density at the focus. When the energy density exceeds a critical value necessary for optical breakdown, there appears luminous plasma, and a shock wave is emitted from the plasma into the bulk liquid. The initial shape of the vapor bubble and the shock front is nonspherical because of reflecting that of plasma. While the plasma relaxes to a vapor bubble, however, several compression waves are emitted following the preceding shock wave, so that both the bubble and the shock front become spherical. The resulting spherical bubble grows under the dominant effect of liquid inertia, and collapses after reaching a maximum size. The high vapor pressure retards the collapse process from the growth and makes the bubble surface rough. While the bubble repeats the growth and collapse processes a few times, that distribution over its surface is amplified through every rebound, eventually breaking up the bubble itself.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.