Photorefractive gratings in liquid crystals with polymer doped C₆₀ layers

Photorefractive-like liquid crystals [1], with their large diffraction efficiencies and nonlinear effects combined with thin film format, are ideal materials for integrated optics applications. Liquid crystals doped with dyes or with added photoconducting polymer layers' show high two-beam coupling gain.The reorientation process that liquid crystal molecules undergo is induced and controlled by the application of light and electric field. There is typically more than one mechanism involved in the reorientation of liquid crystal molecules and, with careful design, the photorefractive space-charge field can play an important role. Moreover, the reorientation can also be strongly influenced by surface-mediated effects and surface-charge modulation, as well as surface anchoring.Photorefractive liquid crystals structures with photoconductive layers on their substrates have shown to be very efficient, in particular using polyvinyl carbazole (PVK) polymer doped with photosensitiser trinitrofluorene (TNF). However, the practical application of this structure is minimised by the toxic nature of the TNF dopant