Scattered circular polarization

Fig. 7.3. Optical layout of the scattered circular polarization (SCP) BioToois ChiralUaman backscattering ROA instrument. Adapted from [25]...

In addition to the choice of the scattering direction, there are three basic polarization schemes [47] for measuring ROA, namely ICP [6] (incident circular polarization), SCP [48] (scattered circular polarization), and DCP [49] (dual circular polarization). All have been experimentally demonstrated. ICP, where the polarization of the exciting light... 

The form of ROA with circular polarization discrimination in the scattered beam and the polarization of the incident beam held fixed in a state a was first measured and referred to as scattered circular polarization (SCP) ROA [32], although it was originally identified and called the degree of circular polarization [33]. The corresponding normalized CID for SCP ROA is given by ... 

Within the harmonic approximation, the Raman, ROA [for a naturally polarized incident light (n) in the scattered circularly polarized (SCP) scheme] [26-28], IR, and VCD [29-32] intensities associated with the pth vibrational normal mode respectively read ... 

Spencer KM, Freedman TB, Nafie LA. Scattered circular polarization Raman optical activity. Chem. Phys. Lett. 1988 149(4) 367-374. 

SCP SOME scattered circular polarization single drop micro-extraction T2DM2 type 2 diabetes mellitus... 

Figure B1.3.A.9. Diagram depicting the angles used in scattermg experiments employing linearly and circularly polarized light. The subscripts i and s refer to the incident and scattered beam respectively.

For a circularly polarized light experiment, one can measure the cross sections for either right (r) or left (1) polarized scattered light. Suppose that right polarized light is made incident on a Raman active sample. The general expressions for the Raman cross sections are [176]... 

Fig. 1. The basic ROA experiment measures a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light. Reprinted from Barron et al., 2000, Prog. Biophys. Mol. Biol. 73,1-49, with permission from Elsevier Science.

The fundamental scattering mechanism responsible for ROA was discovered by Atkins and Barron (1969), who showed that interference between the waves scattered via the polarizability and optical activity tensors of the molecule yields a dependence of the scattered intensity on the degree of circular polarization of the incident light and to a circular component in the scattered light. Barron and Buckingham (1971) subsequently developed a more definitive version of the theory and introduced a definition of the dimensionless circular intensity difference (CID),... 

The other form of optical activity in vibrational transitions is known as Raman optical activity (ROA). Here, also, one measures an intensity difference for left compared to right circularly polarized incident radiation however, optical activity in light scattering has no direct analog in electronic spectroscopy. ROA was first measured by Laurence Barron, A. D. Buckingham, and M. P. Bogaard in 1973 (9) and several reviews of the subject have since appeared (10-14). 

In problems involving optically active particles it is usually more convenient to use the amplitude scattering matrix in the circular polarization representation. The transformation from linearly to circularly polarized electric field components is... 

The cross sections for extinction and scattering by an optically active particle are different for incident left-circularly and right-circularly polarized light. For an optically active sphere, the cross sections can be obtained in a manner similar to that for a nonactive sphere (Section 4.4). Therefore, we give only the results and omit the details ... 

Thus, the difference between the diagonal elements of the forward amplitude scattering matrix in the circular polarization representation has a simple physical interpretation. Although we considered identical particles for conveni-... 

However, (8.25) is not restricted to spheres but holds for particles of arbitrary shape. Thus, circular dichroism in particulate media includes a component that is the result of differential scattering, in contrast with circular dichroism in homogeneous media, which arises solely from differential absorption of left-circularly and right-circularly polarized light. 

Note that the cross polarization is zero and incident unpolarized light does not acquire a degree of circular polarization upon scattering. 

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