Spatial distribution of cluster size and density in supersonic jets as targets for intense laser pulses

Clusters were produced as a result of argon gas cooling during expansion through a supersonic nozzle. A two-dimensional model was set up in order to calculate gas expansion and partial condensation into clusters. Calculations were validated by experimental measurements using Mach-Zehnder interferometry and Rayleigh scattering, and performed with two types of nozzles (Laval and conical nozzles). These optical diagnostics together with numerical simulations led to the cluster size and density determination with spatial resolution through the gas and cluster jet. Cluster production was observed to be very sensitive to the nozzle geometry. Homogeneous gas and cluster jets were produced and characterized using conical nozzle geometry, with cluster density about 1012 per cm3. Due to the fast valve-nozzle connecting geometry, shock waves have been observed at the Laval nozzle throat that strongly affected cluster production on the jet axis. Averaged cluster radius was observed to be easily tunable from 180 to 350 Aa by varying the upstream gas pressure P0 from 20 to 60 bars. A different scaling law, versus P0, has been observed for this regime of large cluster, compared to Hagena's predictions for the small cluster regime