Polymers for Nonlinear Optics

The starting point for nonlinear optics involves the constitutive relationship between the polarization induced in a molecule, P, and the electric field components, E, of the applied constant, low frequency, or optical fields (60). Ignoring magnetic dipoles and higher order multipoles, the induced polarization yields the approximation 

The quantities P and E are vectors, and a, j3, and 7 are tensors. The subscripts arise through the introduction of Cartesian coordinates. 

A similar expression can be written for the polarization induced in an ensemble of molecules, whether in the gas, liquid, or solid state. For this case, the polarization P can be written 

When a polymer is subject to an intense sinusoidal electric field such as that due to an intense laser pulse, Fourier analysis of the polarization response can be shown to contain not only terms in the original frequency co, but also terms in 2(0 and 3 o (60). The intensity of the nonlinear response depends on the square of the intensity of the incident beam for 2co, and the third power for 3 . For the second-order effects, the system must have some asymmetry, as discussed previously. For poling, this means both high voltage and a chemical organization that will retain the resulting polarization for extended periods of time. Polymeric systems investigated have been of three basic types  

Molecules exhibiting large NLO effects are dissolved or dispersed in the polymer, which then merely acts as a carrier (69). An example is 2-methyl-4-nitroaniUne dissolved or dispersed in vinylidene fluoride 

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Barnik, M. L, Blinov, L. M., Weyrauch, T, Palto, S. A., Tevosov, A. A., and Haase, W, Stark spectroscopy as a tool for the characterization of poled polymers for nonlinear optics. In G. A. Lindsay, K. O. Singer, Eds. Polymers for Second-Order Nonlinear Optics, 288 (1995). Natansohn, A., Rochon, R, Gosselin, J., and Xie, S. Azo polymers for reversible optical storage. 1. Poly[4 -[[2-(acryloyloxy)ethyl]ethylamino]-4-nitroazobenzene]. Macromolecules 25,2268 (1992). 

Moroni, M. Le Moigne, J. Luzzati, S. Rigid rod conjugated polymers for nonlinear optics. 1. Characterization and linear optical properties of poly(aryleneethynylene) derivatives. Macromolecules 1994, 27, 562-571. 

Polymer functionalization aims at imparting new properties (e.g. chemical, biophysical, physicochemical or optoelectronic) to materials. Functional polymers have been developed for a wide range of diverse applications. These include organic catalysis (support catalysts), medicine (red-blood-cell substitutes), optoelectronics (conducting polymers, magnetic polymers and polymers for nonlinear optics), biomaterials, paints and varnishes, building materids, photographic materials as weU as lube and fuel additives. While it is not possible to enum ate all of the applications of functional polymers, some representative examples of functional polymers are listed below. 

L.S. Sapochak, D.W. Polls, L.R. Dalton and C.W. Spangler, Asymmetrical diphenylpolyene pendant polymers for nonlinear optical activity. Optical and Electronics Properties of Polymers, MRS Proceedings, Vol. 214, J.A. Emerson and J.M. Torkelson eds., 1991, pp 73-78. 

M. Moroni, Le J. Moigne, S. Luzzati, Rigid Rod Conjugated Polymers for Nonlinear Optics 1. Characterization and Linear Optical Properties of Poly(Aryleneethynylene) Derivatives. Macromolecules 1994,27,562-571. 

Recently, polymers show promising prospects as active constituents of optical and electronic devices, especially polymers for nonlinear optics and conducting polymers. In a remote future even organic ferromagnets and molecular electronics may become more than wishful thinking. For this reason several fundamental aspects of these materials are the subject of intensive research. In this paper we will review the present state of the art in these new fields of polymers for electronics and photonics. Special emphasis will be laid on recent results from our laboratories. 

E. M., and Kitipichai, P., Processable cross-linked polymers for nonlinear optical applications. Mater. Res. Soc. Symp. Proc., 328, 637-642 (1994). 

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