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

Abstract

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.

Multiple ionization of CH3I clusters by nanosecond laser: Electron energy distribution and formation mechanism of multiply charged ions

“…What is the reason for the saturation of electron energy at high laser intensity? As known to us, each cluster contains thousands of molecules [21,22], and the ionization probability of a cluster could be thousand times greater than that of single molecular. It is reasonable to deduce that there will be more than one ionized sites in CH 3 I cluster, especially with high laser intensity and long laser pulse duration.…”

Experimental observation of structural phase transition in CsBr clusters

“…Initial Ar cluster size was first estimated based on the cluster source expansion conditions with the Hagena scaling parameter formalism [45] adjusted by Dorchies et al [46] for * > 10 4 . The number of picked up CsBr monomers by the Ar cluster is then iteratively calculated based on the mean free path of the cluster inside the oven having a certain CsBr vapor pressure [47] determined by the oven temperature.…”

High Intensity Femtosecond XUV Pulse Interactions with Atomic Clusters

“…This jet, with a throat diameter of 500 µm, was backed with a pressure of 13 bar. Using previously published results to ascertain the average size and size distribution of the Xe clusters produced by this jet we estimated that we produced a log-normal distribution of clusters with average size, <N>, ranging up to 10 4 atoms [17]. A Wiley-McLaren [18] time-of-flight (TOF) spectrometer with charged grids mounted around the XUV interaction region allowed us to measure the ion charge state distribution.…”