We show unequivocal evidence for formation of 𝐻𝑒 2 * excimers in liquid He II created by ionizing radiation produced through neutron capture. Laser beams induced fluorescence of the excimers. The fluorescence was recorded at a rate of 55.6 Hz by a camera. The location of fluorescence was determined with an uncertainty of 5 m. The technique provides an opportunity to record the flow of 𝐻𝑒 2 * excimers in a medium with very small viscosity and enables measurement of turbulence around macroscopic liter size objects or vortex matter in three dimensions.The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

Measurement of the injecting time of picosecond laser in indirect-drive integrated fast ignition experiments using an x-ray streak camera Review of Scientific Instruments 90, 033504 (2019);

No abstract

Time dependent observations of point-to-point correlations of the velocity vector field (structure functions) are necessary to model and understand fluid flow around complex objects. Using thermal gradients, we observed fluid flow by recording fluorescence of $${\text{He}}_{2}^{*}$$ He 2 ∗ excimers produced by neutron capture throughout a ~ cm3 volume. Because the photon emitted by an excited excimer is unlikely to be recorded by the camera, the techniques of particle tracking (PTV) and particle imaging (PIV) velocimetry cannot be applied to extract information from the fluorescence of individual excimers. Therefore, we applied an unsupervised machine learning algorithm to identify light from ensembles of excimers (clusters) and then tracked the centroids of the clusters using a particle displacement determination algorithm developed for PTV.