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

We describe in detail an optical interferometer designed for measurements of capillary oscillations of a bubble of gas in a liquid. The stationary oscillation modes are shown to be selectively excited by an electric field with suitable symmetry. The interferometer sensitivity allows accurate measurements in the linear regime, where different bubble modes are decoupled and the existing linearized hydrodynamic treatment can be properly applied. The predicted −3/2 power law dependence of the quadrupolar and octupolar mode frequencies as a function of the bubble radius is found. Data are compared with the existing flat surface capillary frequencies measured by the standard surface light scattering technique.