Nonlinear Optical Effect of Polymer Film Electret

In this article, we discuss the influence of electrical poling methods on nonlinear optical properties of polymer electret film. By comparing different kinds of poling means, it is suggested that charging a polymer film sample at elevated temperature and cooling it in the electric field is a good way for getting a nonlinear optical polymer film electret, because dipoles can be aligned easily and frozen stably in this way. The temperature of polarization should be selected higher than the temperature of glass-transition of the sample. In the poling, many homo-charges are always injected into or near the surface of the film. Although these homo-charges may have no contribution to nonlinear optical coefficients, they produce a large electric field, which is useful for keeping dipole alignment stable