Guo, W., Wright, J. D., Cahn, S. B., Nikkel, J. A. and McKinsey, D. N. (2009) Metastable Helium Molecules as Tracers in Superfluid ^{4}He. Physical Review Letters, 102 (23).
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Metastable helium molecules generated in a discharge near a sharp tungsten tip immersed in superfluid 4He are imaged using a laser-induced-fluorescence technique. By pulsing the tip, a small cloud of He2* molecules is produced. We can determine the normal-fluid velocity in a heat-induced counterflow by tracing the position of a single molecule cloud. As we run the tip in continuous field-emission mode, a normal-fluid jet from the tip is generated and molecules are entrained in the jet. A focused 910 nm pump laser pulse is used to drive a small group of molecules to the first excited vibrational level of the triplet ground state. Subsequent imaging of the tagged molecules with an expanded 925 nm probe laser pulse allows us to measure the flow velocity of the jet. The techniques we developed provide new tools in quantitatively studying the normal fluid flow in superfluid helium.
This is a Submitted version This version's date is: 12/6/2009 This item is not peer reviewed
https://repository.royalholloway.ac.uk/items/ed57223c-7b32-43a8-dea5-6edc55eda92a/1/
Deposited by Research Information System (atira) on 24-May-2012 in Royal Holloway Research Online.Last modified on 24-May-2012