Polarization elliptically polarized light

As discussed above, the reflection of linearly polarized light from a surface generally produces elliptically polarized light, because the parallel and perpendicular components are reflected with different efficiencies and different phase shifts. These changes in intensity and phase angle can be analyzed to characterize the reflecting system. This approach is called ellipsometry. 

In ellipsometric spectroscopy, an elliptically polarized light is allowed to reflect on the interface and the change in ellipticity and phase angle are determined from complex reflectivity. 

Optically active chromophores show different absorption for left and right circular polarized light (where the orientation of the polarized light changes periodically). These substances modify a circular polarized beam in such a way that the light is elliptically polarized after leaving the sample, an effect called circular dichroism. 

Optical activity also manifests itself in small differences in the molar extinction coefficients el and er of an enantiomer toward the right and left circularly polarized light. The small differences in e are expressed by the term molecular ellipticity [9 J = 3300(el — r). As a result of the differences in molar extinction coefficients, a circularly polarized beam in one direction is absorbed more than the other. Molecular ellipticity is dependent on temperature, solvent, and wavelength. The wavelength dependence of ellipticity is called circular dichroism (CD). CD spectroscopy is a powerful method for studying the three-dimensional structures of optically active chiral compounds, for example, for studying their absolute configurations or preferred conformations.57... 

Figure 7.25 Set-up for ellipsometry microscopy. Incident linearly polarized light reflects on the surface and becomes eiliptically polarized. The quarter wave plate converts the polarization from elliptical to linear. The analyzer is placed such that it extinguishes all light. If the reflection properties change because a gas is adsorbed, the polarization does not match the setting of the analyzer and light passes through it. Appropriate lenses project an image of the surface onto the CCD camera (adapted from Rotermund [72]).

Smith, D. Y., 1976. Comments on the dispersion relations for the complex refractive index of circularly and elliptically polarized light, J. Opt. Soc. Am., 66, 454-460. 

Adding LCP and RCP components of different amplitudes, yields elliptically polarized light. The major axis of the ellipsoid is the sum of amplitudes AR and AL, and the minor axis is their difference, as shown in Fig. 5. The ellipticity 0 is defined as the arctangent of the ratio of the minor axis to the major axis ... 

Fig. 5. Elliptically polarized light emerging toward the observer through a circularly dichroic sample. The sign is defined by the chemical convention that

Metallic reflectors do not produce plane-polarization, but when plane-polarized light falls on a polished metal, its vibration is in general changed from a rectilinear to an elliptic one, and the light is said to be elliptically polarized. 

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