Second-harmonic generation , nonlinear polymer applications

In this chapter we deal primarily with experimental results that have been reported dealing with parametric interactions in nonlinear poled polymers, i.e. mostly on second harmonic generation in phase-matched configurations. Because the theoretical analysis associated with these processes has been known for some time and has been independently reviewed many times, we will only briefly overview these basics. Also, the polymeric materials developed for similar applications are reviewed in another section of this book and we refer the reader to that for details. 

Polyphosphazenes are suitable materials to be used as carriers for nonlinear optical (NLO) chromophores. Second order NLO properties have been studied for the polymer (128) and blends of (129) with the free chromophore (130) or the cyclophosphazene (131). All systems have glass transition temperatures higher than 135°C and a wide transparency window. The system (129)-(130) appears to exhibit the highest second-harmonic generation (SHG) response. For possible applications the SHG capability has to be enhanced. ... 

Ferrocene-containing polymers with long spacers have been prepared as new nonlinear optical (NLO) materials for second harmonic generation (SHG) applications (e. g. frequency doubling) [10], The use of ferrocene derivatives in this area is attractive as a result of their demonstrated large hyperpolarizability values combined with their thermal and photochemical stabilities [11], These factors make polyferrocenes desirable candidates for use as processable NLO materials. The polyurethane copolymer 4.4 was synthesized using a functional ferrocene monomer (Eq. 4.1) and has been well-characterized the molecular weight was estimated by GPC to be Mn=7600. The two possible orientations of the ferrocene NLO chromophore monomer unit, which correspond to opposite dipole orientations, were both present in the main chain. 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

Nonlinear Optical (NLO) materials is a relatively new area of chemistry and has caught the attention of both the polymer and organometallic chemist. The use of ferrocene derivatives in NLO applications was first independently studied by two research groups. As anticipated, the metal center in ferrocene was found to serve as an excellent electron-donor. The crystalline compounds (see below) exhibited very high second harmonic generation (SHG) efficiencies relative to urea. ... 

This article introduces the field of nonlinear optics and the electronic nonlinear optical (NLO) response of polymers and pol5mier composites. Both second- and third-order NLO phenomena are included, with primary emphasis on harmonic generation, the intensity-dependent refractive index, and nonlinear (multiphoton) absorption effects. The beginning sections introduce the phenomena and explain how the order of the nonlinearity can be understood from a series expansion of the polarization in powers of the electric-field. In addition to listing the variety of nonlinear optical phenomena and some applications, some of the advantages of polymeric materials for NLO applications are also surveyed. 

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