Technique for characterizing azimuthal anchoring of twisted nematic liquidcrystals using half-leaky guided modes

The half-leaky guided-mode technique is used to explore the director profil e through a thin, twisted, homogeneously aligned nematic liquid-crystal cel l (Merck-E7). Twisted alignment is realized by rubbed polyimide layers on b oth inner walls of the cell. By monitoring first a particular angle of inci dence range of the p-to-s-conversion reflectivity for the twisted-nematic c ell under high voltage, the direction of the liquid-crystal director on the top interface of the cell, the easy axis, is accurately determined. Then b y removing the external voltage and modeling the complete director profile in the cell to fit the half-leaky guided-mode reflectivity data recorded, t he real twist of the director from the top to the bottom of the cell is acc urately determined. By comparing the surface director orientation at zero v olts with the easy axis of the top interface, the azimuthal (in-plane twist ) anchoring coefficient, W-T, is quantified through knowledge of the twist elastic constant K-22 At 26.5 degreesC we find that for E7, W-T = (4.4 +/- 0.3) x 10(-5) J m(-2). (C) 2001 Optical Society of America.