Electronic nonlinear optical applications

Ferroelectric Liquid Crystals Designed for Electronic Nonlinear Optical Applications... 

PPQs possess a stepladder structure that combines good thermal stability, electrical insulation, and chemical resistance with good processing characteristics (81). These properties allow unique applications in the aerospace and electronics industries (82,83). PPQ can be made conductive by the use of an electrochemical oxidation method (84). The conductivities of these films vary from 10-7 to 10-12 S/cm depending on the dopant anions, thus finding applications in electronics industry. Similarly, some thermally stable PQs with low dielectric constants have been produced for microelectronic applications (85). Thin films of PQs have been used in nonlinear optical applications (86,87). 

But, in the general case, inhomogeneities are induced by fast chemical reactions and are very difficult to control. For this reason, precursors of controlled architectures have been developed for different purposes, such as to decrease the viscosity in high-solids systems, to lower shrinkage, to improve material properties and, for some electronic and nonlinear optical applications, to build nanosized ordered regions in the networks. 

Azo-benzene molecules are widely recognized as attractive candidates for many nonlinear optical applications. A highly deformable distribution of the ic-electron gives rise to very lar molecular optical nonlinearitics, Phdto-isomerization of azo molecules allows linear and nonlinear macroscopic susceptibilities to be easily modified, giving an opportunity to optically control the nonlinear susceptibilities. In this chapter, we will discuss third-order nonlinear optical effects related to photoisornerization of azo-dye polymer optical materials. 

Thiophene-containing D-A-substituted jt-systems have been extensively studied in relation to their application in organic electronics. Nonlinear optical (NLO) measurements of such push-pull systems showed enhanced second-order polarizabilities (P) compared with the phenyl counterparts. These increased nonlinearities were attributed to the partial decrease in the aromatic character and increased n-overlap between the thiophene units. Various electron donors (-NR2, -OMe, -SMe) and acceptors (-NO2, -CHO, -S02Me, -CN) have been introduced into the oligothiophene backbone, not only to study the electron and energy transfer processes, but also because of their prospects as active molecules in electronic devices. The... 

The polysilanes represent another class of polymers that has been extensively studied for nonlinear optical applications [62- ]. These polymers have a molecular structure (R,—Si—R2) that is a long catenated a-bonded silicon backbone with two side groups R, and R2, usually carbon based, attached to each Si atom in the backbone chain. They are soluble in most hydrocarbon solvents and thin films of excellent optical quality can be fabricated with conventional spinning and coating techniques. In spite of the o--bonded nature of the backbone, the poly silanes show extensive electronic delocalization, resulting in strong transitions for excitations polarized parallel to the backbone [65]. They are unique in that they are transparent through the visible to the infrared in contrast to the 7r-electron polymers. 

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. 

C. W. Spangler, L. S. Sapochak, and B. D. Gates, Polaron and bipolaron formation in model extended TT-electron systems potential nonlinear optics applications, in Organic Materials for Non-Linear Optics, Vol. I (R. A. Hann and D. Bloor, eds.). Roy. Soc. Chem., London, 1989, pp. 57-63. 

Prasad, P. N. and S. R. Ulrich (eds.), Nonlinear Optical and Electroactive Polymers , Plenum Press, New York, 1988. The use of these polymers for electronics and optical applications. 

SAMs are generating attention for numerous potential uses ranging from chromatography [SO] to substrates for liquid crystal alignment [SI]. Most attention has been focused on future application as nonlinear optical devices [49] however, their use to control electron transfer at electrochemical surfaces has already been realized [S2], In addition, they provide ideal model surfaces for studies of protein adsorption [S3]. 

Because of the generality of the symmetry principle that underlies the nonlinear optical spectroscopy of surfaces and interfaces, the approach has found application to a remarkably wide range of material systems. These include not only the conventional case of solid surfaces in ultrahigh vacuum, but also gas/solid, liquid/solid, gas/liquid and liquid/liquid interfaces. The infonnation attainable from the measurements ranges from adsorbate coverage and orientation to interface vibrational and electronic spectroscopy to surface dynamics on the femtosecond time scale. 

Many of the fiindamental physical and chemical processes at surfaces and interfaces occur on extremely fast time scales. For example, atomic and molecular motions take place on time scales as short as 100 fs, while surface electronic states may have lifetimes as short as 10 fs. With the dramatic recent advances in laser tecluiology, however, such time scales have become increasingly accessible. Surface nonlinear optics provides an attractive approach to capture such events directly in the time domain. Some examples of application of the method include probing the dynamics of melting on the time scale of phonon vibrations [82], photoisomerization of molecules [88], molecular dynamics of adsorbates [89, 90], interfacial solvent dynamics [91], transient band-flattening in semiconductors [92] and laser-induced desorption [93]. A review article discussing such time-resolved studies in metals can be found in... 

Cycloaddition reactions with the Si(lOO) surface have been investigated for the purpose of designing microelectronics, nonlinear optical materials, sensors, and biologically active surfaces. The features of the [2+2] cycloadditions characteristic of the reactions in the pseudoexcitation band [133] predicts that [2+2] cycloadditions of electron-donating alkenes with Si(100)-2 x 1 surface could proceed with retention of configurations, in agreement with the observation [134]. Such stereospecific functionalizations of surfaces are of potential use for specific applications. 

This manuscript describes the dendritic macromolecules for optical and optoelectronic apph-cations, particularly stimulated emission, laser emission, and nonlinear optics. Dendrimers have been designed and synthesized for these applications based on simple concepts. A coreshell structure, through the encapsulation of active imits by dendritic branches, or a cone-shaped structure, through the step-by-step reactions of active imits, can provide particular benefits for the optical high-gain media and nonlinear optical materials. It also described experimental results that support the methods presented for designing and fabricating functionalized dendrimers for optoelectronic applications, and theoretical results that reveal the intermolecular electronic effect of the dendritic structure. 

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