Pulsed helium droplet beams

We report a systematic study of pulsed cryogenic expansion at temperatures ranging from 20 K down to 4.5 K, which enables us to span a large range of helium droplet sizes from similar to 10(5) to similar to 10(11) He atoms, as obtained via titrations of the droplet beam with helium gas at room temperature. The measured peak flux is a factor of one thousand larger than in a continuous beam. Comparison with continuous nozzle results show similar droplet sizes at low T < 6 K, indicating in both cases the droplets are created via the fragmentation of the fluid. (C) 2018 Elsevier B.V. All rights reserved.