  We describe the characterization of a pulsed supersonic rare gas beam which
is intended to serve as an ultracold neutral atom target for the production of
an ultrashort ion pulse via femtosecond photoionization. The velocity
distribution of atoms entrained in the beam is measured and characterized by
temperatures $T_\parallel$ and $T_\perp$ in directions along and perpendicular
to the beam propagation, respectively. It is shown that $T_\perp$ values in the
mK regime are achieved at distances of the order of 1000 mm from the nozzle.
Moreover, the center beam density at this position is measured to be of the
order of $10^{11} atoms/cm^{3}$. Both findings are essential for the intended
application and confirm the targeted beam specifications. Comparison with
theoretical estimates reveals the well-known skimmer interference effect, which
is found to reduce the beam density by more than one order of magnitude.
