Luminescence Spectra of Laser-induced Cavitation Bubbles

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 of only a blackbody continuum. Luminescence from bubbles collapsing between two parallel rigid boundaries also contains OH* emission bands similar to those found in multi-bubble 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 will be discussed in connection with the generation of the OH* radicals.