Half leaky guided wave study of homeotropically aligned ferroelectric liquid crystals

Abstract The optical excitation of half-leaky guided modes has been used to explore in detail the director configuration in a homeotropically aligned ferroelectric smectic, Sc*, liquid crystal. By the application of an in-plane electric field the natural helicity has been unwound providing a simple optical structure for study. As the electrical field is reduced the helical pitch re-establishes itself. By fitting angle dependent reflectivity data obtained for a range of applied fields the Sc* cone angle, the twist elastic constant, B3, and the helical pitch are determined. Because the boundary constraints are so weak in the homeotropically aligned cell, prepared without a surface layer, then the parameters determined for the liquid crystal material in this case, are effectively the ‘free’ material parameters.