Nonlinear optical properties resonant

The discussion in this chapter is limited to cyanine-like NIR conjugated molecules, and further, is limited to discussing their two-photon absorption spectra with little emphasis on their excited state absorption properties. In principle, if the quantum mechanical states are known, the ultrafast nonlinear refraction may also be determined, but that is outside the scope of this chapter. The extent to which the results discussed here can be transferred to describe the nonlinear optical properties of other classes of molecules is debatable, but there are certain results that are clear. Designing molecules with large transition dipole moments that take advantage of intermediate state resonance and double resonance enhancements are definitely important approaches to obtain large two-photon absorption cross sections. 

The linear and nonlinear optical properties of one-dimensional conjugated polymers contain a wealth of information closely related to the structure and dynamics of the ir-electron distribution and to their interaction with the lattice distorsions. The existing values of the nonlinear susceptibilities indicate that these materials are strong candidates for nonlinear optical devices in different applications. However their time response may be limited by the diffusion time of intrinsic conjugation defects and the electron-phonon coupling. Since these defects arise from competition of resonant chemical structures the possible remedy is to control this competition without affecting the delocalization. The understanding of the polymerisation process is consequently essential. 

The nonlinear optical properties are determined using resonance Raman scattering, coherent antistokes Raman scattering and coherent stokes Raman scattering. The two-photon polarizability is found to be very large in these materials. General... 

The simplest description of compoimds of this type is obtained limiting the siun-over-state equations to terms depending only on the properties of the groimd state g and the first excited state e (two-state model) [93]. This is analogous to the two-level model introduced to describe other nonlinear optical properties, for example the nonlinear polarizability pS - co coi,co2) [ 104]. In the case of 2PA, this two-state, or dipolar, contribution to the cross section is, on resonance ... 

In this section the electronic structure of conjugated polymers is discussed. They form a special class of materials with particular types of excitations (such as the solitons) and properties, introduced briefly in Chapter 11. These problems are discussed here essentially in relation to the spectroscopic properties. The related but distinct subject of electrical conductivity is treated in Section IV. To set the scene, we first present some typical results visible absorption and emission spectra and resonance Raman spectra. We consider the theoretical issues in Section III.B, then return to the meaning of the experimental results in Section III.C. The interesting nonlinear optical properties of CPs will be considered in Section III.D. These sections are concerned with electronic states within the gap or near the band edges the structure (i.e., the dispersion relations) of valence and conduction bands is also of theoretical interest and is considered in Section III.E. 

Nonlinear optical properties, 12 Nuclear magnetic resonance, 3, 8 Nucleic acids, 12, 18... 

Dick B, Hochstrasser RM, Trommmsdorf HP (1987) In Chemla DS, Zyss J (eds). Resonant Molecular Optics Nonlinear Optical Properties of Organic Molecules and Crystals, vol 12. Academic, New York, p 159... 

In the past two decades, a significant effort has been made towards development of reliable computational techniques for calculations of nonlinear optical properties of molecules. This has been reflected in many methods for calculations of first-(jS) and second-order (y) hyperpolarizabilities implemented in widely available quantum-chemical packages. However, the purely resonant properties, like two-and three-photon absorptivities have been coded in only a few of them. Also the inclusion of the influence of environment on NLO properties made a significant step forward in comparisons of theoretical and experimental data for large organic systems. 

Among several different approaches to the problem of the evaluation of the nonlinear response of molecular systems, one can distinguish finite field (FF) approaches [28, 47], response theory [89, 90], and sum-over-states (SOS) methods [91, 113], Those three approaches are available in many flavours. In this chapter we shall describe the last approach to the computation of resonant and non-resonant electronic nonlinear optical properties of molecules. 

Grund, A., Kaltbeitzel, A., Mathy. A.. Schwarz, R., Bubeck, C., Vermehren, P., Hanack, M. Resonant nonlinear optical properties of spin-cast films of soluble oligomeric bridged (phthalo-cyaninato)ruthenium(II) complexes. J. Phys. Chem. 96, 7450-7454 (1992)... 

In the above discussion, we have only considered the effects due to the CTE-CTE repulsion, which contribute to the resonant nonlinear absorption (as well as to other resonant nonlinearities) by the CTE themselves. Here, however, we want to mention a more general mechanism by which the nonlinear optical properties of media containing CTEs in the excited state can be enhanced. This influence is due to the strong static electric field arising in the vicinity of an excited CTE, If, for example, the CTE (or CT complex) static electric dipole moment is 20 Debye, at a distance of 0.5 nm it creates a field Ecte of order 107 V/cm. Such strong electric fields have to be taken into account in the calculation of the nonlinear susceptibilities, because they change the hyperpolarizabilities a, / , 7, etc. of all molecules close to the CTE. For instance, in the presence of these CTE induced static fields, the microscopic molecular hyperpolarizabilities are modified as follows... 

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

One subject that attracted much attention is the nonlinear optical properties of these semiconductor nanoclusters [17], The primary objective is to find materials with exceptional nonlinear optical response for possible applications such as optical switching and frequency conversion elements. When semiconductors such as GaAs are confined in two dimensions as ultrathin films (commonly referred to as multiple quantum well structures), their optical nonlinearities are enhanced and novel prototype devices can be built [18], The enhancement is attributed mostly to the presence of a sharp exciton absorption band at room temperature due to the quantum confinement effect. Naturally, this raises the expectation on three-dimensionally confined semiconductor nanoclusters. The nonlinearity of interest here is the resonant nonlinearity, which means that light is absorbed by the sample and the magnitude of the nonlinearity is determined by the excited state... 

It was suggested by Birnholm, Haus and others in 1988 [16], that the surface plasmon resonance would be drastically tunable if the metal was the shell in a core-shell particle, rather than the core. It was also predicted that enhanced nonlinear optical properties would ensue. We now compare the predictions for the surface plasmon mode for these two cases. Firstly, we look at silica coated gold nanocrystals. 

The nonlinear optical properties in solution of selected functionalized PDAs, described herein, have also been evaluated by means of the z-scan technique. Off resonance studies (at 705 nm) show that nonlinear refraction is only comparable to that of the solvent for these dilute solutions, but that nonlinear absorption, characterized by p values, varies significantly, with the nature of the side-chains. O It can be inferred that if bulk films of these PDAs possess suitable nonresonant nonlinear refractive properties for optical devices, modification of side-chain structure can reduce the magnitude of undesirable two photon absorption. 

When a high-intensity laser beam impinges on material, its electromagnetic field induces electrical polarization that gives rise to a variety of nonlinear optical properties, because in this case the higher terms in Eq. (3-4) are not negligible. The determination of the coefficients and that serve to characterize the nonlinear properties is complicated by the fact that they are composed of many elements. With a being equal to two and three, and are composed of 3 = 27 and 81 elements, respectively. Fortunately, these tensors possess symmetry properties that can be invoked to reduce the number of independent elements, for instance, when the optical frequencies involved in the nonhnear interaction are far away from resonance (absorption) [15]. 

In this chapter we will shortly summarize the nonlinear optical properties of macromolecular systems and some of the main experimental techniques for their optical characterization. Some basic optoelectronic patterns will be reported in order to give a brief account of the advances in the realization of active waveguide systems and telecommunication devices based on organic materials. The main optoelectronic devices based on nonlinear optical properties of chromophores in polymeric and hybrid matrices will be illustrated. In particular Mach-Zehnder modulators, microring resonators, switches and wavelength filters will be reviewed. 

NMR. nuclear magnetic resonance non-bridging oxygens (NBO), 25 nonlinear optical properties nonlinear electron polarization, 389 optical Kerr effect, 389 optical susceptibility, 389 second harmonic generation, 389 ultrafast response, 389 non-Newtonian flow, 240 non-oxides, 47... 

The effect of quantum confinement in semiconductors is supported by rigorous theoretical calculations by Brus [27]. The linear and resonant nonlinear optical properties will... 

Modified anilino squaraines have been widely utilized in surface-enhanced Raman resonance scattering (SERBS) spectroscopy. Their molecular structure displays a quadrupole D-A-D system that is characterized by an electron-deficient cyclobutendione (C Oj) bridge (Figure 5.7). The total structure can be represented in many ways, with the charge homogenously distributed over the entire molecule. Several theoretical studies have been conducted on this class of materials and their unusual nonlinear optical properties [4,81]. 

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