Amorphous polymer films containing hyperpolarizable dye molecules are poled by an electric fieldapplied 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 polymerand its trapping by dye species sets up a charge gradient perpendicular to the direction of the external poling field.

The dielectric properties of a liquid-crystalline (LC) copolymer containing photochromic spiropyran groups have been determined over wide ranges of frequency and temperature. The observed loss curves contain a component from the dipole reorientations of the mesogenic groups and a further component from a conductivity-related process. An electrical cleaning method was used to reduce the contribution from the latter process and a subtraction method was devised to separate the overall loss curves into the two components. Using electrical/thermal treatments it was found possible to align the copolymer homeotropically but not planarly. The dielectric loss spectra for unaligned and homeotropically aligned samples were very different. The data were analysed to yield two relaxation parameters for unaligned and aligned samples and were interpreted in terms of the anisotropic motions of dipolar mesogenic groups as have been discussed previously. In addition, the temporal stability of alignment of homeotropic samples at temperatures close to the clearing temperature was determined using the dielectric method.

We report second harmonic generation studies of an amorphous polymer (polymethylmethacrylate) containing hyperpolarizable dye species poled in an in-plane geometry where the electrodes are thinner than the polymer film. It is found that polymers poled in this geometry exhibit optical nonlinearity both parallel and perpendicular to the direction of the poling field. It is determined that charge injection into the film is responsible for the nonlinearity in the perpendicular direction. This nonlinearity is much stronger than that predicted solely on the basis of dipole moment -- poling field interactions.