Organic materials for non-linear optics: inter-relationships between molecular properties, crystal structure and optical properties

An account is given of the origins, in the molecular electronic properties and crystal structure, of the large quadratic optical nonlinearities found in some organic crystals. Particular cases, in which powerful second-harmonic generation or large Pockels effects have been found, chosen to illustrate the influence of different aspects of molecular or crystal structure, are introduced. Three of these, MBANP, NMBA and DAN are described in greater detail in the light of recent experimental and theoretical work.