Rayleigh scattering isotropic

The different symmetry properties considered above (p. 131) for macroscopic susceptibilities apply equally for molecular polarizabilities. The linear polarizability a - w w) is a symmetric second-rank tensor like Therefore, only six of its nine components are independent. It can always be transformed to a main axes system where it has only three independent components, and If the molecule possesses one or more symmetry axes, these coincide with the main axes of the polarizability ellipsoid. Like /J is a third-rank tensor with 27 components. All coefficients of third-rank tensors vanish in centrosymmetric media effects of the molecular polarizability of second order may therefore not be observed in them. Solutions and gases are statistically isotropic and therefore not useful technically. However, local fluctuations in solutions may be used analytically to probe elements of /3 (see p. 163 for hyper-Rayleigh scattering). The number of independent and significant components of /3 is considerably reduced by spatial symmetry. The non-zero components for a few important point groups are shown in (42)-(44). 

Most linear optical phenomena such as refraction, absorption and Rayleigh scattering are described by the first term in Eq. (1) where is the linear susceptibility tensor. The higher order terms and susceptibilities are responsible for nonlinear optical effects. The second-order susceptibility tensor T underlies SFG, whereas and BioCARS arises within As we are concerned with optical effects of randomly oriented molecules in fluids, we need to consider unweighted orientational averages of the susceptibility tensors in Eq. (1). We will show that the symmetries of the corresponding isotropic components and correspond to time-even pseudoscalars the hallmark of chiral observables [2]. 

Hendrickx, E., Clays, K., Persoons. A. Hyper-Rayleigh Scattering in Isotropic Solution, Acc. Chem. Res. 31, 675-683 (1998)... 

Fluctuations in the order parameter are reflected in various physical properties of a liquid crystal material. In this section we will focus on the elastic (Rayleigh) scattering of light by such fluctuations in the isotropic phase of nematic and cholesteric materials near Tc. 

Reduction of the refractive index of the core polymer would serve to reduce Rayleigh scattering loss because this property influences the turbidity of isotropic polymers by a factor of eight. Huorination of the polymer is one method to reduce the refractive index of the mataials. As discussed in Section 7.2.5, the reduction in loss over that of PMMA may be attributed to partial fluorination. The loss limit for partially fluorinated methacrylate polymer was estimated to be 19 dB/km at 568 nm and 58 dB/km at 650 nm. Calculated Rayleigh scattering loss, 9.5 dB/km at 568 nm and 5.5 dB/km at 650 nm, is reduced to about 55% of that of PMMA. In this case, absorption loss, 53 dB/km at 650 nm, is the dominant loss of this polymer. 

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