Enhanced Nonlinear-optical Responses of Disordered Clusters and Composites

1. Introduction Clusters and nanocomposites belong to so-called nanostructured materials. Properties of such materials may be dramatically different from those of bulk materials with identical chemical composition. Confinement of atoms, electrons, phonons, electric fields, etc., in a small spatial region modifies spectral properties (shifts quantum levels, changes transition probabilities), and also changes the interaction between the constituent particles. In this paper we concentrate on an important source of the modification of properties, namely on local fields.