Pressure dependence of argon cluster size for different nozzle geometries

Abstract

We experimentally study Rayleigh scattering from a cluster jet produced by high pressure argon gas expanding into vacuum through four different nozzles (a supersonic slit nozzle, a slit nozzle, a conical nozzle, and a sonic nozzle). The scattering signal intensity and the scattering image are recorded by photomultiplier tube and charge-coupled device camera, respectively. Based on the scattering image, the atom density in the gas flow is estimated. This allows for the comparison of the dependence of average cluster size on argon gas backing pressure between the nozzles. The experimental results show that the planar expansion developed from the supersonic slit and the slit nozzles exhibits the higher atom density than the axisymmetric expansion from the conical and the sonic nozzles. The slit nozzle is shown to have the highest pressure dependence of average cluster size. It is found that the supersonic slit nozzle is more favorable to the large clusters than the slit nozzle under the backing pressure of up to 50 bars, though it has the lower pressure dependence of average cluster size.