The interaction of the antiferroelectric helix with an electric field appli
ed perpendicular to its axis is investigated, A two stage switching process
is observed, in which the helix unwinds to an intermediate state in the pr
etransitional regime, at voltages below the threshold for antiferroelectric
to ferroelectric switching. A series of experimental studies and theoretic
al modelling show that the intermediate state is an antiferroelectric state
in which the directors lie in the plane containing the applied electric fi
eld and the smectic laver normal. The mechanism for the unwinding process i
s the interaction of the applied field with an induced polarisation, which
arises from a distortion to the antiferroelectric ordering.