Optically non-linear and transparent polyimide:barium titanate films-preparation and characterization

Polyimide (PI) films were prepared using water/alcohol soluble polyamic acid. These PI films show about 80% optical transmission in the 600 nm to 1600 nm wavelength range. At room temperature, the dielectric constant was found to be about 3.5 and loss tangent was 0.003. These values do not vary significantly in the range of measurement of temperature or frequency. Optically transparent PI:BT films were prepared by insitu polymerization of PI and gelation of Barium Titanate (BT). The content of BT in the composite is about 15 to 20%. The optical transmission spectra indicates about 75% transmission in the visible range. The X-ray diffractogram shows the formation of crystalline BT, although tetragonality could not be ascertained. Transmission and Scanning electron micrographs show dispersion of ordered BT clusters of micron size in PI matrix. The dielectric permittivity of these films was found to be about 10 with loss of about 0.08. Two-wave mixing and four-wave mixing using Ar-ion laser have been observed in the corona poled composites. The results indicate that poled composite films can be used in nonlinear optical devices