Charge injection asymmetry: A new route to strong optical nonlinearity in poled polymers

Amorphous polymer films containing hyperpolarizable dye molecules are poled by an electric field applied parallel to the plane of the thin film. The resultant second harmonic generation is much stronger than predicted by the standard model of dipolar interactions, and furthermore indicates asymmetry both parallel and perpendicular to the poling field. These results are attributed to a new, efficient mechanism for the production of optical nonlinearity in poled films in which asymmetric charge injection into the polymer and its trapping by dye species sets up a charge gradient perpendicular to the direction of the external poling field.