Molecular crystals and polymers for nonlinear optics

We present new experimental results on second-harmonic generation in highly conjugated organic molecules and molecular crystals recently developed in our group, as well as on electro-optic eftects in thin-film polymers. A large value of the molecular hyperpolarizability of a new hydrazone-type molecule crystallizing in a noncentrosymmetric point group is reported. Large nonlinear optical coefticients of up to 840 ± 200 pmN were measured in crystals of 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). The new experimental results are compared with theoretical calculations of limiting values of nonlinear optical coefticients. Computer modeling of crystal structures shows good agreement with experimental results. Measurements on electro-optic polymers with high thermal stability are presented.