Optical Nonlinearity Of Co-Polymers Caused By Charge Injection

Abstract

We have shown [1] that asymmetric injection of electric charge into polymer-dye blends can induce second order nonlinear optical effects which are distinct from the more conventional mechanism of using electric fields to align the dye molecules. Using an “in-plane” geometry [1], charges can be injected into polymer-dye films causing symmetry breakage both parallel and perpendicular to the external field. The symmetry breakage perpendicular to the field results from the setting-up of a macroscopic charge gradient, while nonlinearity parallel to the field results from conventional dipolar alignment. Using high voltages but only moderate fields (2000 V across 2mm) charge injection effects can be stronger than dipolar alignment. It is believed that charged dimers and quadrupolar nonlinearities are responsible for the nonlinearity in a charge gradient [2].