Luminescence spectra of laser-induced cavitation bubbles near rigid boundaries.

The luminescence spectra of laser-induced cavitation bubbles near rigid boundaries are measured for various relative distances between the bubble and the boundaries. We find that the luminescence spectra of bubbles collapsing near a single boundary consist only of a blackbody continuum. Luminescence from bubbles collapsing between two parallel rigid boundaries contains O H- emission bands similar to those found in multibubble sonoluminescence. In both cases, the bubble interior temperature deduced from blackbody fits decreases with the distance between bubble and boundary. The shape instabilities of the collapse near a boundary and the consequent presence of high-velocity jets inside the bubble at its minimum volume are discussed in connection with the generation of the O H- radicals.