TRAPPING OF SINGLE BUBBLES IN CRYOGENIC FLUIDS

Single bubbles of helium gas of radius 10-20mum have been stably trapped in liquid nitrogen. A spherical acoustic resonator 5.0 cm in diameter is driven with ultrasonic transducers in a radial mode, and the acoustic radiation pressure provides the force holding the bubble at the center of the sphere. It should be possible to use this technique to trap bubbles in other cryogenic fluids such as argon, neon, and helium. Applications of the trapping are discussed, including a search for the emission of sonoluminescence from the bubble, study of the bubble oscillation dynamics using laser scattering, and the prospect of studying charged bubbles.