Polarization of light

For unpolarized light the phases px and (py are imcorrelated and then-difference fluctuates statistically. For linearly polarized light with its eleetric vector in x-direction Aoy = 0. When E points into a direction a against the X axis, (px = Py and tana = Aoy/Aox- For circular polarization Aqx = Aoy and — (py i n/2. 

The different states of polarization can be characterized by their Jones vectors, which are defined as follows  

The Jones representation shows its advantages when we consider the transmission of light through optical elements such as polarizers, A./4 plates, or beamsplitters. These elements can be described by 2 x 2 matrices, which are 

For example, incident light linearly polarized in the x-direetion (a = 0°) becomes, after transmission through a A./4 polarizer with its slow axis in the x-direction 

The transmitted light is cr -light, where the phase factor of tt/2 does not affect the state of polarization. More examples can be found in [2.15-2.17]. 

Wave plate with phaseshift (p 2 nx -direction and —(pl2iny -direction 

Rotator (device which turns the polarization vector by an angle 0) 

The Jones representation shows its advantages when we consider the transmission of light through optical elements such as polarizers, A/4 plates, or beamsplitters (Fig. 2.12). These elements can be described by 2x2matrices Jones matrices), which are compiled for some elements in Table 2.1. The polarization state of the transmitted light is then obtained by multiplication of the Jones vector of the incident wave by the Jones matrix of the optical element. 

If the light wave passes through several polarizing elements their Jones matrices are multiplied, where the first matrix in the product represents the last element. We will illustrate this by some examples  

Linear polarizers Circular polarizers Linear polarizers 

For example, a linearly polarized incident light with a = 0° becomes, after transmission through a circular polarizer, 

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The Fresnel equations predict that reflexion changes the polarization of light, measurement of which fonns the basis of ellipsometry [128]. Although more sensitive than SAR, it is not possible to solve the equations linking the measured parameters with n and d. in closed fonn, and hence they cannot be solved unambiguously, although their product yielding v (equation C2.14.48) appears to be robust. 

The last attribute of tire electromagnetic field we need to discuss is wave polarization. The nature of tire transverse field is such tliat tire oscillating field disturbance (which is perjDendicular to tire propagation direction) has a particular orientation in space. The polarization of light is detennined by tire time evolution of tire direction of tire electric field... 

The varieties of isomerism are summarized in Fig. 16.18. Enantiomeric pairs of optical isomers rotate the plane of polarization of light in opposite directions. 

Enantiomers differ in one physical property chiral molecules display optical activity, the ability to rotate the plane of polarization of light (Section 16.7 and Box 16.2). If a chiral molecule rotates the plane of polarization clockwise, then its mirror-image partner rotates it through the same angle in the opposite direction. 

A competitive fluorescence-polarization immunoassay method was described for the monitoring of 12 drugs including valproic acid [18]. Samples (serum or plasma) were deproteinated. Fluorescence from the fluorescein-labeled analyte used as tracer was excited at 488 nm and polarization of light emitted at 531 nm was measured. The calibration was stable for 4 weeks and the coefficient of variation was below 10%. A single measurement took 8-10 min. 

In recent years, stereochemistry, dealing with the three-dimensional behavior of chiral molecules, has become a significant area of research in modern organic chemistry. The development of stereochemistry can, however, be traced as far back as the nineteenth century. In 1801, the French mineralogist Haiiy noticed that quartz crystals exhibited hemihedral phenomena, which implied that certain facets of the crystals were disposed as nonsuperimposable species showing a typical relationship between an object and its mirror image. In 1809, the French physicist Malus, who also studied quartz crystals, observed that they could induce the polarization of light. 

A rigorous and complete mathematical treatment of the polarization of light and the interaction of light with oriented matter is outside the scope of this chapter. These subjects have been thoroughly dealt with before and can be found in a number of comprehensive texts [29-32] the reader is referred to the excellent book by Michl and Thulstrup [3] for a more detailed treatment of optical spectroscopy with polarized light. Here, a conventional, qualitative representation is given to establish the nomenclature and conventions to be used and to facilitate the understanding of the concepts presented. 

We should also be familiar with the meaning of the term conformational asymmetry. We know that different conformations of the same compound have different symmetry and different statistical contribution (i.e., their percentage content is different). Therefore, the total effect on the polarization of light depends on the arrangement of atoms in different conformations and also on the statistical contribution of each conformation. This is called conformational asymmetry. The compound CH3-CH2-CH (CH3)C1 has conformational asymmetry because two identical atoms (c) are situated at the asymmetric centre. This compound has three staggered conformations. 

Polarization of light Arrangement of the parts which make up a light ray so that they all act in the same way.]... 

When the incident light is horizontally polarized, the horizontal Ox axis is an axis of symmetry for the fluorescence intensity Iy = Iz. The fluorescence observed in the direction of this axis (i.e. at 90° in a horizontal plane) should thus be unpolarized (Figure 5.3). This configuration is of practical interest in checking the possible residual polarization due to imperfect optical tuning. When a monochromator is used for observation, the polarization observed is due to the dependence of its transmission efficiency on the polarization of light. Then, measurement of the polarization with a horizontally polarized incident beam permits correction to get the true emission anisotropy (see Section 6.1.6). 

Polarization effects The transmission efficiency of a monochromator depends on the polarization of light. This can easily be demonstrated by placing a polarizer between the sample and the emission monochromator it is observed that the position and shape of the fluorescence spectrum may significantly depend on the orientation of the polarizer. Consequently, the observed fluorescence intensity depends on the polarization of the emitted fluorescence, i.e. on the relative contribution of the vertically and horizontally polarized components. This problem can be circumvented in the following way. 

The aligned-DNA, transparent, self-standing, and flexible film is of interest as a new naturally-occurring functional material, as well as an anisotropic conductive film. For example, the DNA-lipid film is effective as an adsorption filter of carcinogens such as acridine orange and ethidium bromide. The aligned-DNA film also shows polarization of light. 

Sir David Brewster 1781-1868, Scottish physicist famous for his researches on tire absorption, reflection, refraction, and polarization of light, and on doubly refracting crystals. One of the founders of the British Association for die Advancement of Science. He invented the kaleidoscope and improved the stereoscope. His optical researches led to great improvement in the construction of lighthouses. 

In terms of beam delivery, the DLW method is based on optical microscopy, confocal microscopy [4,6,13] and laser tweezers [14] (for reviews on laser tweezers see [ 15,16]). These techniques allow for a high spatial 3D resolution of a tightly focused laser beam with optical exposure of micrometric-sized volumes via linear and nonlinear absorption. In addition, mechanical and thermal forces can be exerted upon objects as small as 10 nm molecular dipolar alignment can be controlled by polarization of light in volumes of with submicrometric cross-sections. This circumstance widens the field of applications for laser nano- and microfabrication in liquid and solid materials [17-22]. 

Figure 5.2 Degree of polarization of light scattered by a sphere small compared with the wavelength for incident unpolarized light.

Figure 14.6 Observed linear polarization of light from several stars Xmax is the wavelength at which the maximum polarization Pmax occurs. From Coyne et al. (1974).

Perrin, F., 1942. Polarization of light scattered by isotropic opalescent media, J. Chem. Phys., 10, 415-427. 

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