Nonlinear Interactions of Light with Liquid Crystals

摘要

Crystals are solids in which the molecules are arranged in clearly defined 3D patterns. Liquid crystals are substances whose constituent molecules retain the spatial regularity of solid crystals, but, at the same time, have the freedom of motion of molecules of a conventional liquid. Common usage of liquid crystals includes household appliances such as microwave ovens, CD players, or thermometers and even wrist watches, but they have an increasingly visible application as the main component in LCD monitors. In fact, the acronym 'LCD' stands for liquid crystal display. Liquid crystals can be classified by the type of directional and positional ordering of the constituent molecules into several categories (phases), of which the most common is the nematic phase. This is the type used in LCD monitors, and is the object of our study. The molecules of a nematic liquid crystal have a cylindrical shape, and can move randomly. Having one axis longer than the other two, it makes sense to talk about orientation of these molecules, which can be modeled mathematically by a unit vector field called director. The one defining property of nematics is that in the absence of external factors such as electro-magnetic fields, or temperature fluctuations, the director is roughly spatially invariant.