Electric field induced isotropic-nematic-smectic A phase transitions, Kerr
effect and fluctuations.
Under a strong electric field, dielectric anisotropy variations have two main contribution: (i) a
linear one originating from quenching of the nematic director fluctuations and (ii) a quadratic
contribution from the Kerr effect. The dependence on temperature and field, and the role of
these contributions on the : isotropic--nematic, isotropic—smectic, and nematic--smectic-A
transitions are analysed by birefringence measurements under strong electric fields up to 5 105
V/cm. The critical or tricritical points of the transitions are localized, non spontaneous phases
are induced and experimental evidence of the Halperin-Lubensky-Ma effect has been
observed.
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