Characterization of argon cluster jets for laser interaction studies

Abstract Atomic clusters can be produced from rare gas, by spontaneous condensation during its expansion and cooling in a supersonic nozzle. When irradiated by intense laser pulses, these near-solid density clusters were observed to absorb a large fraction of the laser energy, leading to the production of highly charged ions. Based on this interaction regime, several international research groups have already demonstrated the ability to produce intense and highly repetitive X-ray and neutron sources without debris, with a relatively small experimental setup. In order to understand the different mechanisms involved in laser – cluster interaction, a complete characterization is needed for the target composed by clusters and surrounded by gas. We present a method based on two different optical diagnostics (Mach–Zehnder interferometry and Rayleigh scattering) and supported by a numerical simulation describing the gas expansion and cluster growth in the nozzle. The study was performed considering argon expanding in two types of nozzles: a Laval and a conical one. The experimental spatial profiles were observed to be in good agreement with the simulations, leading to spatial resolution of gas density, cluster size and cluster density.