Nonlinear optical polymer electrets

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 centro-symmetry 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. On the other hand, methods specifically developed for nonlinear optical materials (e.g. electro-optical measurements or second-harmonic generation) may-at least in principle-also be used to study any polar electret material