A Laser system for flow field imaging in superfluid helium using He$_{2}$*

For visualization of the flow field in superfluid Helium (He II), He$_{2}$* excimer can be traced by using Laser induced fluorescence (LIF). In our group the proposed He$_{2}$* excimer generation method is based on the neutron absorption reaction of naturally abundant $^{3}$He in Helium. Small He$_{2}$* clusters generated by this method are then available for 3D LIF imaging. By applying this method, we already confirmed successful generation of He$_{2}$* excimers using our laser system. In this study, for successful visualization of He$_{2}$* excimer images in superfluid Helium, the required laser parameters, such as f intensity, repetition rate and wavelength were investigated. For systematic characterization of these, an offline system based on a high voltage discharge for excimer generation is being set up to provide a more intense and accessible source of excimers, not requiring the use of a neutron beam.