Probing luminescence from nonspherical bubble collapse

The luminescence from single laser produced cavitation bubbles for varying degrees of asphericity is investigated temporally, spatially, and spectrally. The degree of asphericity is controlled with an adjustable rigid boundary near the bubble. Temporally, single and multiple light emission events happen during a time interval of 80 ns. The luminescence duration increases with increasing asphericity. Spatially, the emissions from nonspherically collapsing bubbles display a pronounced halo around the central spot several times larger than the luminescence from spherical collapse. Spectrally, the ratio of the line to continuum emission of the sodium doublet is enhanced, whereas the total emitted energy decreases by four orders of magnitude as compared to the spherical collapse. These findings point towards emission not only from the bubble interior but also from the liquid surrounding the bubble.