Application of Liquid Crystals for tunable Photonic Crystals

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The project which is proposed here, is devoted to the investigation of spatially periodic nanostructures where one of the components is a liquid crystal. It is well known that liquid crystals are birefrigent, and that their refractive indices depend strongly on temperature. Moreover, the optical axis can be reoriented by applying electric and magnetic fields. Since the photonic bandgap depends strongly on the refractive indices of the corresponding media, it is in principle possible to vary the optical properties of a photonic crystal containing a liquid crystal by changing the temperature or the external magnetic or electric field. The practical possibilities and limits of this effect shall be studied in the proposed project. We plan to study three different types of model systems: In the first place, we plan to infiltrate a liquid crystal in colloidal crystals ("artificial opals") and inverse colloidal crystals and to study the effect of external fields on these structures. As a second type of system, we wish to study microfabricated structures in silicon or aluminium oxide which are filled with a liquid crystal. The methods of investigation include the spectroscopic and electrooptic characterization, diffraction experiments with convergent light, and near-field scanning optical microscopy (NSOM). The third type of systems consists of liquid crystals exhibiting a lattice-like superstructure. These materials will be used in order to study the influence of a spatially periodic environment on the emission of organic dye molecules.