FLUORESCENT CONFOCAL MICROSCOPY EXPLORATION OF 3D LIQUID CRYSTAL STRUCTURES

Liquid crystal displays are at the forefront of low power methods for displaying information. Because of the massive flat screen market place much research is still going on into the use of liquid crystals in optical displays, and some of the latest generation of devices use a radically different approach to that of the conventional twisted nematic displays. Instead of requiring a voltage to be maintained to produce the dark (or light) state, the devices are constructed from surface relief grating substrates that produce a director alignment that varies in two or even three dimensions. This results in two optically distinct stable states at zero applied voltage, one appearing dark under crossed polarisers, and the other, light. Power only needs to be applied to switch between these states. Two such structures currently in development for commercial applications are the zenithal bistable device (ZBD), developed by ZBD displays, and the post aligned bistable device (PABN) developed by Hewlett-Packard. To understand fully the behaviour of the liquid crystal director in these new structures we here propose to use Fluorescence confocal microscopy (FCM). For conventional translationally invariant structures the best techniques for unravelling the director structure are optical waveguide techniques, pioneered in Exeter. However, the resolution in the plane of the substrate is limited by the diameter of the probing laser beam to a few microns and further it cannot be used to probe the full three dimensional profile found in the new periodic structures. As the structures used to control the liquid crystal material move from one-dimension to two-dimensions we here propose a characterisation technique required to study them which follows suit.