ABSTRACT
Today, inorganic crystals are the completely dominating materials for nonlinear optics (NLO) applications. The interest in organic materials for NLO has been constantly growing due to several factors. First of all, the polarization response to an externally applied field is of molecular electronic origin and, therefore, practically lossless and extremely rapid. Ultrafast, nonresonant nonlinearities in combination with relatively low value of dielectric permittivity can be found in organic single crystals, but these are expensive to grow. Polymer materials are cheap, but normally have very low polar order. Here, liquid crystals and liquid crystalline polymers have a particular interest due to their inherent order. While nematics show some peculiar effects which can be described as macroscopic, the polar smectics have a nonlinear response on the microscopic, electronic level which is fairly similar to what is found in crystals. We first briefly introduce the basic concepts and then discuss macroscopic and electronic effects in turn.
