Bubbles, Drops, and Vortices in Cryogenic Liquids

这个凝聚态物理项目研究了在水、乙醇和液态氩等液体中产生的瞬态激光气泡的特性。当气泡坍缩时，里面的气体被压缩和加热，在最小半径的坍缩点处产生快速的发光脉冲。将测量发光的光谱，并对崩溃点附近的气泡动力学进行高分辨率研究，从而详细了解发光机制的性质及其与声致发光的关系。第二个令人感兴趣的领域是由液氦表面下的超声波换能器产生的超流体雾。将对这些新型气溶胶进行研究，以检查它们是否与普通雾有显著差异。在雾中进行声衰减测量，以检查与液滴中超流体第二声模式的耦合。第三个感兴趣的领域是亚单层氦-4膜吸附在新型介孔硅陶瓷衬底MCM-41上的超流体相变。这种衬底具有长而均匀的圆柱形孔隙，孔径在18至100埃之间的材料可以被制造出来。这将允许涉及量子化涡旋对的超流体跃迁理论得到检验，并且应该允许测量这些亚单层超流体中的涡旋核心大小。这项研究将有助于培养几名研究生的博士学位。他们将学习在许多不同的科学技术领域有用的广泛技能，包括低温技术、声学方法、激光和光谱学的应用。这个凝聚态物理项目包括三个不同的活动。其中一种是将脉冲激光聚焦到一个点上，在水、乙醇和液态氩等液体中产生气泡。当气泡破裂时，里面的气体被压缩和加热，产生了快速的光脉冲。光的光谱将被测量，气泡运动将被研究。这将使人们了解光发射的本质，以及它与一种被称为声致发光的类似现象之间的关系。在第二个项目中，将研究液氦上方蒸汽中产生的雾的性质。由于构成雾的液滴是超流体，所以这个系统不同于普通的雾。声音在雾中的衰减将被测量，以检查是否有任何耦合到液滴中的超流体波。在最终项目中，将研究极薄氦膜（厚度小于原子层）的超流体性质。这些薄膜被吸附在一种新型的衬底上，这种衬底是二氧化硅陶瓷，它有长长的圆柱形孔，孔径非常小，直径只有几十个原子。这项工作将测试陶瓷中超流体特性的理论，并将允许测量超流体的基本参数。这项研究将有助于培养几名研究生的博士学位。他们将学习在许多不同的科学技术领域有用的广泛技能，包括低温学、声学、激光和光学的应用。

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.