The characterization of a high-density gas jet

We have measured the density profiles of a pulsed gas jet expanding into vacuum in order to characterize its suitability as a target for laser-plasma interaction studies. A Mach-Zehnder interferometer has been used to measure the densities for gas-reservoir pressures in the range (1-5) x 10(4) Torr with 1 and 1.75 mm diameter opening nozzles in N-2 and Ne gas. N-2 and Ne gas jets with the same nozzle opening were found to produce similar density profiles. The axial and radial density profiles of the gas jet are presented and shown to fit well to simple self-similar profiles with an exponentially decreasing density with the distance from the gas jet nozzle and Gaussian-shaped radial density profiles. It is shown that such profiles can be expected for the free expansion of a low-viscosity fluid into vacuum.