Imaging Fluorescence of He2* Excimers Created by Neutron Capture in Liquid Helium II

We show unequivocal evidence for formation of He₂^* excimers in liquid He II created by ionizing radiation produced through neutron capture. Laser beams induce fluorescence of the excimers. The fluorescence is recorded at a rate of 55.6 Hz by a camera. The location of the fluorescence is determined with an uncertainty of 5 μ m . The technique provides an opportunity to record the flow of He₂^* excimers in a medium with very small viscosity and enables measurement of turbulence around macroscopic liter size objects or vortex matter in three dimensions.