Preparation and characterization of polyimide and optically non-linear transparent polyimide: ceramic films

Transparent polyimide films (PI) were prepared and their dielectric and optical properties were studied. The PI films show almost 80% transmission in the 600 nm to 1600 nm wavelength range. The dielectric constant was found to be about 3.5 and it does not vary significantly upto 160°C. Transparent PI:BaTiO₃ and PI:LiNbO₃ films were prepared by in situ polymerization of PI and gelation of BaTiO₃ and LiNbO₃ sols respectively. The X-ray diffractograms clearly indicate the formation of BaTiO₃ and LiNbO₃ in these films. The dielectric constant of PI:BaTiO₃ films was found to be 10 and its variation with temperature shows a Curie peak at about 120°C. The dielectric constant of PI:LiNbO₃ films was found to be about 6. The loss is very small in these films. In PI:LiNbO₃ films, optical phase conjugation using degenerate four wave mixing technique has been observed and the experimental results are given. It is concluded on the basis of the results that these films may find useful applications in non linear optical devices