This is an experimental condensed matter physics project whose goal is to understand how bubbles are formed in liquid helium when the liquid is in a state of tension. When an electron is introduced into liquid helium, it forces open a small cavity in the liquid. This "electron bubble" has a radius of approximately 20 A. Application of a negative pressure to the liquid causes this bubble to grow, and at a critical pressure the bubble becomes unstable and explodes. It is planned to study how the pressure required to cause the explosion of the bubble changes when the electron is optically excited to different quantum states. The results of these measurements will be compared with theoretical calculations already completed. As part of the experimental study it is planned to also measure the lifetime of the different excited states of the electron. In a second project the effect of quantized vortices on the nucleation of bubbles in superfluid helium will be investigated. The research provides excellent training for graduate students who utilize state-of-the-art instrumentation to study fundamental physics problems which have implications for a number practical circumstances where bubble formation is important. %%% Bubbles form in liquid as a result of a number of different processes. They can be produced when the pressure on a liquid that contains gas is reduced, when a can of Coca Cola is opened, for example. Bubbles also form in the turbulence around the propeller of a ship, and when a liquid is heated above its boiling point. In some situations bubble production has undesirable effects. For example, over the course of time the bubbles produced near to the propeller of a ship damage the propeller. On the other hand, bubble generation can also be very useful, as in an ultrasonic cleaner. The long range goal of this research is the study of how bubbles are formed and how to control the formation for technological advantage. Experiments will be performed to investigate bubble production in liquid helium under a number of different conditions. Liquid helium is chosen for these experiments because it can be produced with exceptional purity, and so effects that might arise from impurities in the liquid can be controlled or eliminated. In the next stage of this research, the effect of electrons and vortices on bubble formation will be studied. The research provides excellent training for graduate students who utilize state-of-the-art instrumentation to study fundamental physics problems which have implications for a number practical circumstances where bubble formation is important.
