Study of Cholesteric Textures in Phase Change Devices by Laser Light Diffraction

Photographic-recording and photomultiplier-recording laser light diffractometers have been constructed and used to study the cholesteric textures in phase change devices as a function of applied voltage and device parameters. The focal conic texture formed with increasing voltage gives diffraction peaks corresponding to 2π rotations of the director, whereas the texture formed by slow nucleation with decreasing voltage also gives “superlattice” lines corresponding to a 4π repeat, due to the different local structures of the textures combined possibly with tilting of the director. The repeat distances obtained by indexing the diffraction patterns agree well with microscopical and infra-red reflectance observations. Laser light diffraction appears to be a powerful technique for quantitative study of the non-uniform unwinding and re-forming of cholesteric twist in an electric field.