GUIDED-WAVE STUDY OF ELECTROCLINIC EFFECTS IN A HOMOGENEOUSLY ALIGNEDSMECTIC-A LIQUID-CRYSTAL

Using the half leaky guided mode geometry, we have studied the electro clinic effect using a thin homogeneously aligned layer of C8, a materi al having a first order S-A to S-C transition in the bulk. Applicatio n of voltage in the SA phase produces a small (< 12 degrees), but easi ly measured director twist which is characterized over a range of temp eratures in the SA phase. Mean field theory is used to interpret the d ata recorded. At low applied fields (less than or equal to 6V mu m(-1) ), a linear voltage dependence of induced twist is found. For higher a pplied fields there is a non-linear dependence which is caused by an i nduced first order S-A to S-C transition at these fields. Fitting the voltage dependent induced twist yields the first three Landau coeffic ients for this transition. The voltage dependent results also provide a procedure for determining the S-A to S-C phase transition.