Polarized light defined

Another measurement, circular dichroism, CD, is caused by a difference in the absorption of right and left circularly polarized light, defined by the equation... 

Figure 2 Elliptically polarized light defined by the azimuth a and the ellipticity i...

Polarimetry. Polarimetry, or polarization, is defined as the measure of the optical rotation of the plane of polarized light as it passes through a solution. Specific rotation [ a] is expressed as [cr] = OcjIc where (X is the direct or observed rotation, /is the length in dm of the tube containing the solution, and c is the concentration in g/mL. Specific rotation depends on temperature and wavelength of measurement, and is a characteristic of each sugar it may be used for identification (7). 

A depolarization measurement consists of exciting a fluorescent sample with linearly polarized light and measuring the polarization of emitted light at right angles to the plane of excitation. The polarization of the emitted light is defined as... 

Ever since Pasteur s work with enantiomers of sodium ammonium tartrate, the interaction of polarized light has provided a powerful, physical probe of molecular chirality [18]. What we may consider to be conventional circular dichroism (CD) arises from the different absorption of left- and right-circularly polarized light by target molecules of a specific handedness [19, 20]. However, absorption measurements made with randomly oriented samples provide a dichroism difference signal that is typically rather small. The chirally induced asymmetry or dichroism can be expressed as a Kuhn g-factor [21] defined as ... 

FIGURE 27.24 Reflection of polarized light. The plane of incidence is defined by the incident and reflected beam. The and p components are indicated for the incident light, with the electric vector normal and parallel, respectively, to the plane of incidence. (From Muller, 1973, with permission from Wiley-VCH.)... 

The fluorescence depolarization technique excites a fluorescent dye by linearly polarized light and measures the polarization anisotropy of the fluorescence emission. The fluorescence anisotropy, r, is defined as... 

Linear Dichroism. In this technique, the DNA molecules are aligned either by an applied electric field pulse or in a flow gradient. The orientation of the aromatic residues of the metabolite model compounds bound to the DNA (either covalently or non-covalently) relative to the orientation of the DNA bases is probed utilizing linearly polarized light. The linear dichroism A A can be either negative or positive, and is defined as... 

If polarized light passes through a medium that exhibits optical rotation, the motion along one of the circular vectors is slower than that of the other. The resultant vector is thus displaced from the original vector by some angle, . Figure 16.5 shows the vector model in which the phase difference is [Pg.588]

The optical transition moments for vibrational or electronic transitions between defect states have specific orientations with respect to the defect coordinates. The absorption strength of polarized light for each of the differently oriented centers is proportional to the square of the component of the transition moment that is along the polarization direction. Hence, a stress-induced redistribution of the defects among their different orientations will be detected as an anisotropy in the polarized optical absorption. A convenient measure of the anisotropy is the dichroic ratio, defined as... 

In the case of synthetic optically active polymers, the intuitive meaning of a CD signal intensity is very similar to that of UV spectroscopy, with the additional dimension of the subtracted absorption between left and right circularly polarized light.37 Absorption of light obeys the Beer-Lambert law, and thus CD intensity is defined as Ae = eL - eR = (AL - AR)/cl, where Ae is the... 

In microscopy, an azimuth is an angle measured relative to a north-south axis of the microscope tube. Normally, the primary north-south axis divides the visible field into left and right sides and corresponds to a position of 0° on the first polarizer, usually below the substage condenser. Be careful if the orientation of the visible field has been altered by microscope accessories (such as cameras), which is why Bennett (26) defined the 0° axis relative to the stand of the microscope. From the 0° position, we follow the convention used in the mathematics of polar coordinates, moving counterclockwise to increment the angles. Points of the compass also are used to describe the orientations of components used for polarized light microscopy, and are abbreviated to N, S, E, and W. 

Define plane-polarized light, optical rotation, optical activity, asymmetric carbon atom, enantiomers, racemic mixture, polarimeter, and specific rotation. 

The concept of transition moment is of major importance for all experiments carried out with polarized light (in particular for fluorescence polarization experiments, see Chapter 5). In most cases, the transition moment can be drawn as a vector in the coordinate system defined by the location of the nuclei of the atoms4 therefore, the molecules whose absorption transition moments are parallel to the electric vector of a linearly polarized incident light are preferentially excited. The probability of excitation is proportional to the square of the scalar product of the transition moment and the electric vector. This probability is thus maximum when the two vectors are parallel and zero when they are perpendicular. 

According to fluorescence selection rules, only molecules that have their absorption dipoles properly oriented with the electronic dipole of polarized light can be excited.(31) Consequently, the emission is also initially polarized. The polarization, P, is defined by the expression... 

Experiments involving anisotropy of phosphorescence or of the absorption of the triplet state rely upon the same principles as the measurement of fluorescence anisotropy. All are based upon the photoselection of molecules by polarized light and the randomization of polarization due to Brownian motion occurring on the time scale of the excited state. Anisotropy is defined as... 

Polarimetry is defined as the quantitative measurement of a change in the direction of the vibration of plane-polarized light during its passage through an optically anisotropic substance or its solution33. 

Fig. 6.23. The direction of the electric-field vector of the electromagnetic wave defines the direction of polarization. In the upper diagram, the electric-field vector travels in the y-direction (y-polarized light), and in the lower diagram, in the x-direction (x-polarized light).

Define the following terms used in Section 6.2 (a) single crystal, (b) polycrystalline solid, (c) in situ technique, (d) ex situ technique, (e) diffraction pattern, (f) infrared radiation, (g) s-polarized and p-polarized light, and (h) radioactive isotope. (Gamboa-Aldeco)... 

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