Selective reflection in ferroelectric liquid crystals distorted by an electric field

Selective reflections were measured to study the elastic deformation of a ferroelectric chiral smectic C liquid crystal in a homeotropically aligned cell when a D.C. electric field was applied normal to the helical axis. The first, second and third order reflections which occur corresponding to the full pitch were detected very clearly. From the dependence of the pitch on the electric field, a torsional elastic constant for the deformation and a critical electric field to unwind the helix were evaluated.