Homeotropic polar anchoring energy of a nematic liquid crystal using the fully leaky waveguide technique

Optical excitation of a series of fully leaky guided modes has been used to explore the director distortion of a hybrid-aligned nematic liquid crystal with a negative dielectric anisotropy (Merck-BDH, MLC 6608) under applicat ion of an ac electric field. Hybrid alignment is realized by the use of a l ecithin film on the top glass plate and rubbed polyimide on the bottom plat e, both plates having indium-tin-oxide coatings. Continuum theory is used t o model the director profile through the cell. Fitting the fully leaky guid ed mode data both in transmission and reflection using optical multilayer t heory together with continuum modeling gives the director profile both with and without applied fields. From this fitting the changes in the surface t ilt angle and its gradient are obtained. Using this information the polar a nchoring coefficient of the homeotropic surface W-theta is deduced. At 23.1 degreesC we find W-theta=(4.6 +/- 0.2) x 10(-4) J m(-2) (C) 2000 American Institute of Physics. [S0021-8979(00)08224-4].