Imaging and time-resolved study of laser-induced fluorescence of dysprosium atoms injected into superfluid helium

We study the time evolution of the cloud of Dy atoms dispersed in superfluid helium and investigate the possibility of using these atoms as tracers for the imaging of superfluid-helium flows. The atoms are produced by pulsed laser ablation and are visualized via their laser-induced fluorescence. It turns out that the observation time is limited by the optical pumping of the atomic population into a nonabsorbing metastable state which is also responsible for the saturation of the fluorescence yield observed earlier.