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Metastable helium molecules as tracers in superfluid 4He
1Physics Department, Yale University, New Haven, CT 06515, USA.
Physical Review Letters
|August 8, 2009
Summary
Researchers visualized metastable helium molecules in superfluid helium using laser-induced fluorescence. This technique allows for precise measurement of normal-fluid velocity in superfluid helium flows.
Area of Science:
- Low-temperature physics
- Quantum fluids
- Atomic and molecular physics
Background:
- Superfluid helium-4 (4He) exhibits unique quantum phenomena, including quantized vortices and frictionless flow.
- Understanding the behavior of the normal fluid component is crucial for characterizing superfluid dynamics.
- Direct visualization and velocity measurements of fluid components in superfluids are experimentally challenging.
Purpose of the Study:
- To develop and demonstrate novel techniques for imaging and measuring the velocity of normal fluid in superfluid 4He.
- To investigate the dynamics of metastable helium molecules in superfluid environments.
- To provide quantitative tools for studying superfluid flow phenomena.
Main Methods:
- Generation of metastable helium molecules (He2*) in superfluid 4He using a pulsed or continuous discharge near a tungsten tip.
- Laser-induced fluorescence (LIF) imaging for visualizing molecule clouds.
- A pump-probe laser scheme (910 nm pump, 925 nm probe) for tagging and tracking molecules.
- Analysis of molecule cloud displacement to determine normal-fluid velocity.
Main Results:
- Successful imaging of He2* molecule clouds in superfluid 4He.
- Demonstration of tracing molecule cloud positions to determine normal-fluid velocity in heat-induced counterflow.
- Observation and velocity measurement of a normal-fluid jet generated in continuous field-emission mode.
- Quantification of molecule entrainment and velocity within the normal-fluid jet.
Conclusions:
- The developed LIF technique provides a powerful new tool for quantitative studies of normal fluid flow in superfluid helium.
- Metastable helium molecules can be effectively used as tracers for flow visualization and velocity measurements.
- These methods open avenues for detailed investigations into the complex dynamics of superfluid systems.
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