A GUIDED-WAVE STUDY OF THE VOLTAGE-DEPENDENT DIRECTOR CONFIGURATION IN A NEMATIC LIQUID-CRYSTAL LAYER WITH FINITE SURFACE TILT

Prism coupling techniques have been used to excite optical modes in a thin nematic liquid crystal with finite surface tilt in order to study the voltage dependent director profile. The surface tilts are opposit e in character and it is found that at zero applied volts the stable c onfiguration is the substantially horizontal state. On applying the fi eld this state is broken, probably transforming to the twisted vertica l state. By modelling all the data obtained, the detailed behaviour of the director profile has been fully characterized yielding much infor mation, including the change of surface tilt with applied voltage. For the nematic liquid crystal E7, this gives a voltage induced surface t ilt of approximately 0.67-degrees V-1 for a 5.65 mum thick cell. Also using a boundary layer model, it has been possible to analyse the free energy in the cell and hence show that the observed twisted vertical state is the expected stable state under the field applied.