Second-order nonlinear optical applications

Chiral Materials for Second-Order Nonlinear Optical Applications... 

CHIRAC MATERIALS FOR SECOND-ORDER NONLINEAR OPTICAL APPLICATIONS... 

Ashwell, G.J. (1999) Langmuir-blodgett films Molecular engineering of noncentrosymmetric structures for second order nonlinear optical applications. Journal of Materials Chemistry, 9, 1991-2003. 

Aramaki, S., Ogawa, T., Ono, N., and Sugi, K. 1993. 3-Nitrochromenes for second order nonlinear optical applications. Journal of the Chemical Society, Chemical Communications, 23 1781-2. 

Blanchard PM, Mitchell GR. 1993a. A comparison of photoinduced poling and thermal poling of azo dye doped polymer films for second order nonlinear optical applications. Appl Phys Lett 63(15) 2038 2040. 

The poled polymer approach is state-of-the-art in terms of the application of polymers to electro-optic devices such as modulators and waveguides. Chromophore-bound polymers for second-order nonlinear optical applications with glass transition temperatures greater than 320°C have been reported (5). However, the electro-optic coefficients are modest, typically less than 10 pm/V at 1.3 im. Part of the poling problem is caused by electrical conductivity at high poling temperatures, which reduces the poling field, or worse, sometimes causes dielectric breakdown. 

S. R. Marder and J. W. Perry, Molecular materials for second-order nonlinear optical applications, Adv. Mater., 5, 804-815 (1993). 

Verbicky JW (1988) Polyimides. In Encyclopedia of polymer science and engineering, vol 12. Wiley, New York, pp 364r-383 Verbiest T, Borland DM, Jurich MG, Lee VY, Miller RD, Volksen W (1995) Exceptiomlly thermally stable polyimides for second-order nonlinear optical applications. Science 268 1604 1606... 

The polymers containing nonlinear optical moieties are considered to be essential for the development of photonic devices. These polymeric materials have second-order nonlinear optical applications, and current research is described in detail in Chapter 10. In succession. Chapter 11, contains a review of ion-conducting polymers. This article depicts how macromolecules can be used as solvents for electrolytes, instead of the usual low molecular weight solvents. Recent studies on the use of polymer electrolytes as the media for electrochemical reactions are presented. 

The focus of the present chapter is the application of second-order nonlinear optics to probe surfaces and interfaces. In this section, we outline the phenomenological or macroscopic theory of SHG and SFG at the interface of centrosymmetric media. This situation corresponds, as discussed previously, to one in which the relevant nonlinear response is forbidden in the bulk media, but allowed at the interface. 

The applications of this simple measure of surface adsorbate coverage have been quite widespread and diverse. It has been possible, for example, to measure adsorption isothemis in many systems. From these measurements, one may obtain important infomiation such as the adsorption free energy, A G° = -RTln(K ) [21]. One can also monitor tire kinetics of adsorption and desorption to obtain rates. In conjunction with temperature-dependent data, one may frirther infer activation energies and pre-exponential factors [73, 74]. Knowledge of such kinetic parameters is useful for teclmological applications, such as semiconductor growth and synthesis of chemical compounds [75]. Second-order nonlinear optics may also play a role in the investigation of physical kinetics, such as the rates and mechanisms of transport processes across interfaces [76]. 

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

Second-order nonlinear optics (NLO) has several applications in the field of optoelectronics.11 Several of these nonlinear processes are straightforward to experimentally demonstrate but their application in devices has been hampered by the lack of appropriate materials. Necessary requirements for second-order nonlinear optical materials include the absence of centrosymmetry, stability (thermal and mechanical), low optical loss, and large and fast nonlinearities.8... 

The study of chiral materials with nonlinear optical properties might lead to new insights to design completely new materials for applications in the field of nonlinear optics and photonics. For example, we showed that chiral supramolecular organization can significantly enhance the second-order nonlinear optical response of materials and that magnetic contributions to the nonlinearity can further optimize the second-order nonlinearity. Again, a clear relationship between molecular structure, chirality, and nonlinearity is needed to fully exploit the properties of chiral materials in nonlinear optics. 

Serious attempts to use LB films in commercial applications include the use of lead stearate as a diffraction grating for soft x-rays (64). Detailed discussion on applications of LB films are available (4,65). From the materials point of view, the ability to build noncentrosymmetric films having a precise control on film thickness, suggests that one of the first applications of LB films may be in the area of second-order nonlinear optics. Whereas a waveguide based on LB films of fatty acid salts was reported in 1977, a waveguide based on polymeric LB films has not yet been commercialized. 

Applications of Organic Second-Order Nonlinear Optical Materials... 

The results are to some extent inconclusive and suggest that a two-photon state may have to be included. Also reported here are some further major improvements in molecular second order nonlinearities of particular importance to poled-polymer electrooptic applications (EO). Thus, it is found that appropriate replacement of benzene moieties with that of thiazole in certain azo dyes results in a factor of three increase in i-p, the molecular dipole ( io) projected molecular second order nonlinear optical susceptibility, p. 

In general, the optimization of organic molecules for third order nonlinear optical applications has enjoyed much less success than for second order optical nonlinearities. The major reason for this has been the questionable validity of the two-level model for y, and the difficult assessment of the contribution of two-photon states for the more acceptable three-level model. 

For some further discussion on the applicability of linear free energy relationships to second order nonlinear optics, see Ulman, A. J. Phvs. Chem. 1988, 92, 2385-2390. 

For the practical application of second-order NLO materials, not only a high hyperpolarizability but also good thermal stability is required. Heteroaryl diazo chromophores could also act as organic second-order nonlinear optical materials suitable for applications such as second... 

The supramolecular structure of block co-polymers allows the design of useful materials properties such as polarity leading to potential applications as second-order nonlinear optical materials, as well as piezo-, pyro-, and ferroelectricity. It is possible to prepare polar superlattices by mixing (blending) a 1 1 ratio of a polystyrene)-6-poly(butadiene)-6-poly-(tert-butyl methacrylate) triblock copolymer (SBT) and a poly (styrene)-Apoly (tert-butyl methacrylate) diblock copolymer (st). The result is a polar, lamellar material with a domain spacing of about 60 nm, Figure 14.10. 

Several papers and patents deal with the preparation of pyrrole-, indole-, and carbazole-derived dyes for application in organic laser device production, coloring of textiles and other materials, photography, analytical chemistry and physiological and organ function monitoring. Sulfonyl-substituted 2-[4-(dialkylamino)phenyliminomethyl]pyrrole dyes have been prepared, for example, 50-53, and their ultraviolet-visible (UV-Vis) absorptions, second-order nonlinear optical properties, and thermal stabilities have been described <1999TL2157>. 

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