Guided wave study of electroclinic effects in a homogeneously aligned smectic A liquid crystal

Abstract

Using the half leaky guided mode geometry, we have studied the electroclinic effect using a thin homogeneously aligned layer of C8, a material having a first order S_A to S∗_C transition in the bulk. Application of voltage in the S_A phase produces a small (< 12°), but easily measured director twist which is characterized over a range of temperatures in the S_A phase. Mean field theory is used to interpret the data recorded. At low applied fields (6 V μm⁻¹), a linear voltage dependence of induced twist is found. For higher applied fields there is a non-linear dependence which is caused by an induced first order S_A to S∗_C transition at these fields. Fitting the voltage dependent induced twist yields the first three Landau coefficients for this transition. The voltage dependent results also provide a procedure for determining the S_A to S∗_C phase transition.