IN-SITU OBSERVATION OF THE ORIENTATIONAL MOTION OF CHROMOPHORES DURING CORONA POLING OF ELECTROOPTIC POLYIMIDES

The corona poling process of electra-optic polymers has been investiga ted for rodlike aromatic polyimides doped with nonlinear optical chrom ophores. The dynamics of the chromophores in poling during and after i midization was observed by measuring second harmonic generation (SHG) from the polymer. In the course of poling during imidization, the SHG, observed before imidization, decreases to zero, reappears, and increa ses as the temperature increases. When poling was after imidization, t he SHG intensity increased monotonically with increasing temperature. The disappearance of SHG in the poling during imidization is probably due to the known structural change in the polymer chains during imidiz ation and the subsequent reorientation of the chromophores caused by f ormation of sheets of polyimides. The characteristics of the samples p oled during and after imidization are nearly the same in both the exte nt of the nonlinear susceptibility and their thermal stability.