Second-order NLO materials

Materials for Frequency Doubling. Second-order NLO materials can be used to generate new frequencies through second harmonic generation (SHG), sum and difference frequency mixing, and optical parametric oscillation (OPO). The first, SHG, is given in equation 3. 

An applied electric field can also change a material s linear susceptibility, and thus its refractive index. This effect is known as the linear electro-optic (LEO) or Pocket s effect, and it can be used to modulate light by changing the voltage applied to a second-order NLO material. The applied voltage anisotropically distorts the electron... 

On the microscopic scale, overwhelming evidence suggest that, in the absence of unusual delocalized excited states, for which there is very little evidence in organic second order NLO materials, the expression for f) for almost all dyes is descibed by a simple two state model via the following expression (6)... 

In the view of the practical use, polymeric materials are expected to overcome the disadvantages of organic molecular crystals in mechanical properties and processability. Most polymers are usually in a symmetric structure as a whole, so they should be considered as third-order rather than second-order NLO materials, except for poled polymer systems. 

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... 

One of the important applications of second-order NLO materials is obtaining of tunable laser sources. Second harmonic generation or sum frequency generation systems lead to monochromatic sources. The optical parametric oscillators are based on the parametric generation of two waves with frequencies co (signal) and CO (idler). In noncentrosymmetric materials an incident photon with frequency co creates two photons satisfying the energy... 

The main requirement for molecule-based second-order NLO materials is a non-centrosymmetric organization of the constituent active species. Furthermore, organic... 

Second-order NLO materials with superb stability based on semi-IPN and IPN systons have been demonstrated. The high rigidity of polymer backbones, increased crosslinking density, and interpenetrating network architecture are important factors for the material design and development. The relaxation behavior of the IPN system was found to be fundamentally different fiem that of a guesl/host system. 

Azobenzene-dye-, stilbene-dye-, or polyene-dye-functionalised polymers have been investigated as second-order NLO materials materials), showing efficient NLO characteristics with low absorption loss [44]. In this case, the dye in the polymer should be aligned in a specific direction to possess second-order optical non linearity. For that purpose, a high electric field... 

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