Old and new poling techniques for nonlinear optical polymer electrets

Polymers with second-order optical nonlinearities contain molecular dipoles as guest molecules, side groups, or main-chain segments. Macroscopic nonlinear optical effects including the electro-optical effect are obtained only after preferential orientation of the dipoles by means of poling. At least in principle, the full range of known electret poling techniques can be employed with nonlinear optical polymer electrets. In addition, a few new poling methods were developed specifically for them. Since relatively high glass-transition temperatures are required for stable amorphous nonlinear optical polymers, poling must usually be performed at elevated temperatures. In addition to the often used classical electrode and corona poling techniques, electron-beam poling was recently proposed for selective poling of nonlinear optical polymers. Furthermore, new poling methods such as photothermal poling with local heating by a light beam and photo-induced poling exploiting the photo-isomerism of molecular dipoles are being introduced. These poling techniques will be discussed and compared, and the possible use of the newly developed methods on other electrets will be considered.