Bubbles, Drops, and Vortices in Cryogenic Liquids

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

This condensed matter physics project investigates the properties of transient, laser-produced bubbles that are created in liquids such as water, ethanol, and liquid argon. As the bubble collapses, the gas inside is compressed and heated, giving rise to emission of a fast pulse of luminescence at the minimum-radius collapse point. The spectrum of the luminescence will be measured, and high-resolution studies of the bubble dynamics near the collapse point should lead to a detailed understanding of the nature of the light-emission mechanism and its relation to sonoluminescence. A second area of interest is superfluid fog generated by an ultrasonic transducer under the surface of liquid helium. These novel aerosols will be investigated to examine if there are significant differences from normal fogs. Sound attenuation measurements in the fog will be undertaken to examine the coupling to the superfluid second-sound mode in the droplets. The third area of interest is the superfluid phase transition of submonolayer helium-4 films adsorbed on a new mesoporous silica ceramic substrate known as MCM-41. This substrate has long uniform cylindrical pores, and materials can be fabricated with pore diameters between 18 and 100 Angstroms. This will allow theories of the superfluid transition involving quantized vortex pairs to be be tested, and should allow a measurement of the vortex core size in these submonolayer superfluids. This research will contribute to the Ph.D. training of several graduate students. They will learn a broad range of skills useful in many different fields of science and technology, including cryogenic techniques, acoustics methods, and applications of lasers and optical spectroscopy. This condensed matter physics project involves three different activities. In one, a pulsed laser focused to a point is used to create bubbles in liquids such as water, ethanol, and liquid argon. As the bubble collapses, the gas inside is compressed and heated, giving rise to a fast pulse of light. The spectrum of the light will be measured, and the bubble motion will be studied. This will allow an understanding of the nature of the light emission, and how it is related to a similar phenomenon known as sonoluminescence. In the second project, the properties of fogs generated in the vapor above liquid helium will be investigated. Since the droplets making up the fog are superfluid, this system is different from ordinary fogs. The attenuation of sound in the fog will be measured, to examine if there is any coupling to the superfluid waves in the droplets. In the final project superfluid properties of very thin helium films (less than an atomic layer in thickness) will be studied. These films are adsorbed on a new type of substrate, a silica ceramic, which has long cylindrical pores, with very fine pore diameters that are only tens of atoms in diameter. The work will test theories of the superfluid properties in the ceramic, and will allow fundamental parameters of the superfluid to be measured. This research will contribute to the Ph.D. training of several graduate students. They will learn a broad range of skills useful in many different fields of science and technology, including cryogenics, acoustics, and applications of lasers and optics.