Field-Induced Spatial Deformations in Chiral Smectic A Liquid Crystals

The application of an electric field to an electroclinic liquid crystal (ELC) causes the molecules to tilt, permitting efficient modulation of an optical signal. This electroclinic tilt also leads to a reduction of the smectic layer thickness, thus introducing strain and causing the planes to deform in order to accommodate the change in the layer thickness. When the ELC is viewed under a polarizing microscope, a spatial modulation of the transmission is observed.1-5 The resulting stripe texture is generally depicted as a triangular deformation of the smectic layer, where a deformation angle equal to the electroclinic (EC) tilt angle preserves the interlayer spacing.5 In this paper, the relationship of the deformation angle and the EC tilt angle is investigated by measuring the field dependence of the transmission of an ELC placed between crossed polarizers. The measured extinction is sensitive to the molecular alignment and is therefore a useful probe of the field induced deformation.