  We study the free expansion of a pancake-shaped Bose-condensed gas, which is
initially trapped under harmonic confinement and containing a vortex at its
centre. In the case of a radial expansion holding fixed the axial confinement
we consider various models for the interactions, depending on the thickness of
the condensate relative to the value of the scattering length. We are thus able
to evaluate different scattering regimes ranging from quasi-three-dimensional
(Q3D) to strictly two-dimensional (2D). We find that as the system goes from
Q3D to 2D the expansion rate of the condensate increases whereas that of the
vortex core decreases. In the Q3D scattering regime we also examine a fully
free expansion in 3D and find oscillatory behaviour for the vortex core radius:
an initial fast expansion of the vortex core is followed by a slowing down.
Such a nonuniform expansion rate of the vortex core may be taken into account
in designing new experiments.
