Second-order non-linearity

Unlike linear optical effects such as absorption, reflection, and scattering, second order non-linear optical effects are inherently specific for surfaces and interfaces. These effects, namely second harmonic generation (SHG) and sum frequency generation (SFG), are dipole-forbidden in the bulk of centrosymmetric media. In the investigation of isotropic phases such as liquids, gases, and amorphous solids, in particular, signals arise exclusively from the surface or interface region, where the symmetry is disrupted. Non-linear optics are applicable in-situ without the need for a vacuum, and the time response is rapid. 

Here we have described two second-order non-linear spectroscopies, SFG in detail and hyper-Raman scattering briefly. 

O—H bonds, hydrogen atom abstraction from, 9,127 Organic materials for second-order non-linear optics, 32,121 Organic reactivity, electron-transfer paradigm for, 35, 193 Organic reactivity, structure determination of, 35,67... 

In recent years a number of organic materials having second order non-linearity of the same order and greater than that of commonly used inorganic materials have been reported. These... 

As an alternative to planar waveguiding structures we report here the fabrication of crystal cored fibres in which it is possible to maintain uniform guide dimensions over long lengths. These fibres with organic crystal core material having large second order non-linearity could be used for miniaturization of visible laser sources and realization of parametric amplifiers for optical communications. 

For an organic material to show electro-optical activity it must exhibit high second order non-linear behaviour. This is one of the terms in the equation that defines the polarisation (u) of an organic molecule as shown below, where E is the perturbing electric field. 

One requirement for second-order non-linearity in optical molecules is that they exhibit non-centrosymmetric symmetry, i.e. they must be dipolar in nature and all point in the same direction. Hence, materials suitable for electro-optical uses should have high figures for the multiplier where p is the dipole moment and P the molecular second order optical non-linearity parameter. ... 

It may be emphasized here that such an elaboration is possible for any small amplitude perturbation technique. It is only necessary to explicitize either the first-order current or the first-order interfacial potential, corresponding to the type of perturbation, to be able to derive expressions for 7q, 1 and AEl. So, the treatment is also useful to estimate the error due to second-order non-linearity in the step methods. However, a separate measurement of the second-order effect can only be done with (sinusoidal) a.c. perturbation. In Table 5, the explicit expressions for SF pertaining to the four methods mentioned in Sect. 2.4.1 are given in such a way that the connection between them is clearly shown. 

Organic Materials for Second-Order Non-Linear Optics... 

Frequency doubling, and second-order non-linear polarization,... 

Light-emitting electrochemical cells, and OLEDs, 12, 175 Light-emitting molecules, by G-H bond activation, 10, 244 Light propagation, and second-order non-linear polarization, 12, 104... 

PNA, bioorganometallic studies, 1, 902 P2N2 dianionic macrocycle, in organometallic synthesis, 1, 69 7yV,P-tridentate ligands, in platinum(II) complexes, 8, 537 Pockels effect, and second-order non-linear polarization,... 

The boundary value problem (Eqs. (10), (11)) is usually solved numerically. However, it is also possible to use another approach employing a linearization of this second-order, non-linear problem and a subsequent analytical treatment The analytical solution of the linearized boundary value problem in the film region is obtained in [15] ... 

Second order non-linear optical properties have been reported for a variety of TTF donor-acceptor compounds <02T7463> and the palladium complex 84 is a room-temperature semiconductor <02CL936>. Preparation of the zinc and cadmium compounds 85 has been reported <02CC1474> and aromatic fused TTFs such as 86 form thin films with useful electrical properties <02JAP265466>. A ferromagnetic interaction occurs in the salt of a TTF... 

Second-order non-linear optics continne to be an area of research becanse of its tremendous potential in the design of photon-based new materials for optical switching, data manipulation, and information processing [12]. 

If the electric field(s) are large (e.g. laser light), subsequent terms in the expansion become important. The third term is the one Aat is of importance in the present work. It is the second-order non-linear polarization,... 

Vibrational sum-frequency spectroscopy (VSFS) is a second-order non-linear optical technique that can directly measure the vibrational spectrum of molecules at an interface. Under the dipole approximation, this second-order non-linear optical technique is uniquely suited to the study of surfaces because it is forbidden in media possessing inversion symmetry. At the interface between two centrosymmetric media there is no inversion centre and sum-frequency generation is allowed. Thus the asynunetric nature of the interface allows a selectivity for interfacial properties at a molecular level that is not inherent in other, linear, surface vibrational spectroscopies such as infrared or Raman spectroscopy. VSFS is related to the more common but optically simpler second harmonic generation process in which both beams are of the same fixed frequency and is also surface-specific. 

Equation (6) shows that the sum-frequency intensity is dependent on the second-order polarization However, that polarization is a vector quantity P f. Within the electric dipole approximation the local fields E and re coupled by the second-order non-linear susceptibility, [16], inducing the following non-linear polarization at... 

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