Second-order materials

Many classes of second-order material appHcations can be envisioned by noting the sinusoidal nature of electromagnetic radiation and rewriting equation 2... 

Commercial frequency doublers have rehed on inorganic materials. The commercial future of doublers depends on not only the improvement in second-order materials but also the development of diode lasers capable of operating in the visible frequency domain. 

Second order materials will be used in optical switching (modulation), frequency conversion (SHG, wave mixing) and electro-optic applications, especially EO modulators (SLM). The applications all rely on the manifestation of... 

Many other organic and some organometallic materials have been examined by the powder SHG method and/or tested by EFISH techniques. They will not be discussed in detail here but are listed by structural classes for completeness. Several compendia of materials responses have been published. (38,54,55) Clearly, the largest single class of second order materials consists of donor-acceptor substituted aromatics. The class has been extended to stilbenes and diarylacetylenes and... 

The development of highly active third-order nonlinear optical materials is important for all-optical signal processing. In contrast to second-order nonlinear optical molecular systems, there are few rational strategies for optimizing the third-order nonlinear optical response of molecular materials. Unlike second-order materials, there exist no molecular symmetry restrictions for the observation of a third-order nonlinear optical response. It is the instantaneous... 

Second-order materials which exhibit quadratic effects such as SHG or electrooptic (EO) switching (in which the refractive indices of EO materials can be modulated by application of an electric static field). The materials must be non-centrosymmetric at both microscopic and macroscopic levels. 

Some Structure-Property Relationships for Third-Order Poiymers and MacromoieCUieS. The preferred approach for developing dipolar second-order materials has been to find optimized chromophores and incorporate these... 

Equations of this kind are called linear constitutive equations. The derivatives of the dependent variables with respect to the independent ones represent material coefficients. Recalling Eqs. (4.8), (4.9), and (4.10) they may also be written as partial second derivatives of the appropriate thermodynamic potential. Because of this second-derivative properly these coefficients are called second-order material coefficients. 

Table 4.3 Interrelations between second order material coefficients...

This shows directly that the nonlinearity of the dynamic resporrse is due both to geometrical nonlinearities (in conjimction with second-order material constants) and to material nonlinearities as expressed by the various third-order constants. 

SHG is certainly one of the most direct techniques able to characterize NLO properties of second order materials. By using polarized radiation incident on a nonlinear material, being the direction 3 the optical axis of the nonlinear material with reference to Fig. 3.3, it can be shown that SH intensity for the two polarizations (S and P) is given by [23] ... 

A liquid polymer, poly[(phenyl isocyanate)-co-formaldehyde, containing one isocyanate group on each of the phenyl rings, was used to cross-link with an optically active second-order material of 4-[ AT-(2-hydroxyethyl)-A -methylamino phenyl]-4 -[(6-hydroxyhexyl)sulfonyl]azobene [146] (Scheme 17). The corona-poled and thermally developed polymer films revealed a... 

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