In situ observation of the orientational motion of chromophores during corona poling of electro-optic polyimides

The corona poling process of electro-optic polymers has been investigated for rodlike aromatic polyimides doped with nonlinear optical chromophores. The dynamics of the chromophores in poling during and after imidization 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 increases as the temperature increases. When poling was after imidization, the 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 imidization and the subsequent reorientation of the chromophores caused by formation of sheets of polyimides. The characteristics of the samples poled during and after imidization are nearly the same in both the extent of the nonlinear susceptibility and their thermal stability.