  Intense, ultrashort pulses of 800 nm laser light (12 fs, $\sim$4 optical
cycles) of peak intensity 5$\times$10$^{14}$ W cm$^{-2}$ have been used to
irradiate gas-phase Xe$_n$ clusters ($n$=500-25,000) so as to induce multiple
ionization and subsequent Coulomb explosion. Energy distributions of exploding
ions are measured in the few-cycle domain that does not allow sufficient time
for the cluster to undergo Coulomb-driven expansion. This results in overall
dynamics that appear to be significantly different to those in the many-cycle
regime. One manifestation is that the maximum ion energies are measured to be
much lower than those obtained when longer pulses of the same intensity are
used. Ion yields are cluster-size independent but polarization dependent in
that they are significantly larger when the polarization is perpendicular to
the detection axis than along it. This unexpected behavior is qualitatively
rationalized in terms of a spatially anisotropic shielding effect induced by
the electronic charge cloud within the cluster.
