  Reciprocal space measurements of spin diffusion in a single crystal of
calcium fluoride (CaF$_2$) have been extended to dipolar ordered states. The
experimental results for the component of the spin diffusion parallel with the
external field are $D_{D}^{||}=29 \pm 3 \times 10^{-12}$ cm$^{2}$/s for the
[001] direction and $D_{D}^{||}=33 \pm 4 \times 10^{-12}$ cm$^{2}$/s for the
[111] direction. The diffusion rates for dipolar order are significantly faster
than those for Zeeman order and are considerably faster than predicted by
simple theoretical models. It is suggested that constructive interference in
the transport of the two spin state is responsible for this enhancement. As
expected the anisotropy in the diffusion rates is observed to be significantly
less for dipolar order compared to the Zeeman case.
