A laser interferometer for the study of electrically excited bubble capillary modes

We describe in detail an optical interferometer designed for measurements o f capillary oscillations of a bubble of gas in a liquid. The stationary osc illation modes are shown to be selectively excited by an electric held with suitable symmetry. The interferometer sensitivity allows accurate measurem ents in the linear regime, where different bubble modes are decoupled and t he existing linearized hydrodynamic treatment can be properly applied. The predicted -3/2 power law dependence of the quadrupolar and octupolar mode f requencies as a function of the bubble radius is found. Data are compared w ith the existing flat surface capillary frequencies measured by the standar d surface light scattering technique. (C) 2001 Elsevier Science B.V. All ri ghts reserved.