Nonlinear optical polymer electrets current practice

Amorphous polymers with strong second-order optical nonlinearities contain molecular chromophore dipoles as guest molecules, as side groups, or as main-chain segments. In order to break the inherent centrosymmetry of the initially isotropic dipole orientation in these materials and to render them nonlinear optically active (as well as piezo- and pyroelectric), preferential dipole alignment by means of electrical poling is necessary. After poling the nonlinear optical polymer films are molecular dipole electrets so that the full range of techniques for the preparation and investigation of polar electrets may be employed, together with nonlinear optical techniques, originally developed for the investigation of ferroelectric polymers, such as poly(vinylidene fluoride). The field of nonlinear optical polymers developed from very enthusiastic beginnings in the early eighties to the present and more realistic approach, with real applications just about to appear.