  We present studies of the magnetic field distribution around the vortices in
LuNi2B2C. Small-angle neutron scattering measurements of the vortex lattice
(VL) in this material were extended to unprecedentedly large values of the
scattering vector q, obtained both by using high magnetic fields to decrease
the VL spacing and by using higher order reflections. A square VL, oriented
with the nearest neighbor direction along the crystalline [110] direction, was
observed up to the highest measured field. The first-order VL form factor,
|F(q10)|, was found to decrease exponentially with increasing magnetic field.
Measurements of the higher order form factors, |F(qhk)|, reveal a significant
in-plane anisotropy and also allow for a real-space reconstruction of the VL
field distribution.
