Detection and Imaging of He_2 Molecules in Superfluid Helium

TL;DR

This paper demonstrates a new optical detection method for He_2 molecules in superfluid helium, enabling imaging and potential applications in turbulence visualization and radiation detection.

Contribution

It introduces a cycling transition technique with repumping lasers for efficient detection and imaging of metastable He_2 molecules in superfluid helium.

Findings

Successful imaging of He_2 molecules in superfluid helium

Mitigation of vibrational limitations using repumping lasers

Potential for new ionizing radiation detectors

Abstract

We present data that show a cycling transition can be used to detect and image metastable He$_2$ triplet molecules in superfluid helium. We demonstrate that limitations on the cycling efficiency due to the vibrational structure of the molecule can be mitigated by the use of repumping lasers. Images of the molecules obtained using the method are also shown. This technique gives rise to a new kind of ionizing radiation detector. The use of He$_2$ triplet molecules as tracer particles in the superfluid promises to be a powerful tool for visualization of both quantum and classical turbulence in liquid helium.