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 nozzles͒. 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 10 12 per cm 3 . 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 Å by varying the upstream gas pressure P 0 from 20 to 60 bars. A different scaling law, versus P 0 , has been observed for this regime of large cluster, compared to Hagena's predictions for the small cluster regime.

The acceleration of electrons injected in a plasma wave generated by the laser wake eld mechanism has been observed. A maximum energy gain of 1.6 MeV has been measured and the maximum longitudinal electric eld is estimated to 1.5 GV/m. The experimental data agree with theoretical predictions when 3D e ects are taken into account. The duration of the plasma wave inferred from the number of accelerated electrons is of the order of 1 ps. 41.75. Lx,52.40.Nk Typeset using REVT E X 1