Optic cavitation in an ultrasonic field.

Cavitation bubbles are generated in water by low-energy femtosecond laser pulses in the presence of an ultrasonic field. Bubble dynamics and cavitation luminescence are investigated by CCD photography and photomultiplier measurements in dependence on the phase of the acoustic cycle at which the bubbles are generated. The experimental results demonstrate that the initially small laser-generated bubbles can be expanded significantly by the sound field and that weak cavitation luminescence can be observed in two small intervals of the seeding phase. The luminescence yield sensitively depends on the degree of sphericity of bubble collapse.