Controlled growth of Helium nanodroplets from a pulsed source

Factors affecting the size of liquid-heliumdroplets produced by a pulsed nozzle are described. The shape of the nozzle orifice is found to be important in allowing control of the size of the droplets. With an appropriate choice of nozzle geometry, the average droplet size is shown to be continuously variable over nearly two orders of magnitude by adjustment of the helium gas stagnation pressure and/or temperature. A scaling law similar to, but not identical with, that found for heliumdroplets produced by continuous supersonic expansion sources is found for the pulsed source. The pulsed nozzle described in this article has been used to make heliumdroplets ranging in size from a few thousand atoms up to nearly 10^5 helium atoms.