Polarisation plane

Fig. 8. Principle of the magnetooptical read-out of domain patterns by the polar Kerr effect. The polarisation plane of the incoming laser beam is rotated clock- or counterclockwise according to the orientation (up or down) of the magnetic moments.

The influence of a magnetic field on gaseous atoms induces a splitting of each line into several polarised components. This phenomenon, which can be seen in the emission or absorption spectra of these atoms and is called the Zeeman effect, arises from perturbations in the energy states of electrons in the atom (Fig. 14.13). For example, the absorption wavelength of cadmium, situated at 228.8 nm, leads to three polarised absorption bands due to the Zeeman effect. One of these bands, the it component, retains the initial value of the wavelength whereas the other two, the a components, are symmetrically shifted by a few picometres relative to the 7r component in a 1-tesla field. The direction of polarisation of the 7r and a lines are perpendicular and the polarisation plane of the 7r component is parallel to the magnetic field (Fig. 14.14). 

If a polarizer which rotates the polarisation plane of the incident wave is placed between two crossed linear polarizers (Fig. 2.13) the electric vector of the input beam will be turned and the crossed polarizer transmits only a fraction of the input intensity which depends on the turning angle 9 of the rotating polarizer. The Jones formahsm yields the output electric vector as... 

Angle between polarisation plane and dipping direction... 

A linearly polarized wave, travelling through a fluid rotates its polarisation plane an angle = o represents the molecular contribution while s describes the... 

Commercial amyl alcohol is contained in fusel oil from fer mentation and consists mainly of isobutyl carbinol together with about 13 per cent, of secondary butyl carbinol, which renders the liquid optically active. It turns the plane of polarisation to the left (see p. 116). 

The polarimeter is an instrument with which the essential oil chemist cannot possibly dispense. The hypothesis, first seriously enunciated by Le Bel and van t Hoff, that substances which contained an asymmetric carbon atom i.e. a carbon atom directly united to four different atoms or radicles) were capable of rotating the plane of polarisation of a beam of polarised light, has now become a fundamental theory of organic chemistry-. The majority of essential oils contain one or more components containing such a carbon atom, and so possess the power of effecting this rotation. In general, the extent to which a given oil can produce this effect is fairly constant, so that it can be used, within limits, as a criterion of the purity or otherwise of the oil. 

Figure 1.53 shows diagrammatically various types of pits that can range from hemispherical with a polished surface, in which crystallographic etching has been completely suppressed, to crystallographic pits whose sides are composed of the crystal planes that corrode at the slowest rate. Pits formed on Ni during anodic polarisation in an acetic acid-acetate buffer of pH 4-6 are shown in Fig. 1.54. 

A substance displays optical activity Molecules of the substance are asymmetrical. Interactions between the molecules and electromagnetic radiation is such that the plane of polarisation of the radiation is always rotated in the same direction... 

Enantiomer A single form of an optically active compound. Optically active compounds usually (but not exclusively) contain one or more chiral centres. Enantiomers are defined by their ability to rotate the plane of beam of polarised light one way or the other and these are referred to as either D or L , or alternatively + or, depending on whether the polarised light is rotated to the right (Dextro) or the left (Levo). 

A further complication is that for a carbon, which has four different groups attached to it in a tetrahedral arrangement, there are two optical isomers called laevo (l-) and dextro (d-) from their different abilities to rotate the plane of polarised light. They are structural mirror images which cannot be superimposed ... 

Consider a linearly polarised monochromatic light ray incident on a metal surface. Such a ray can always be resolved into two orthogonal components and if the plane of reflectance at the metal is chosen as the reference, then these components correspond to S- and P-polarised light, as discussed in the previous section. 

Figure 2.58 shows the S and P-components of a ray polarised at 45° to the plane of reflection incident at a metal surface this will be the polarisation state of the incident light assumed throughout the discussion below. On being reflected both the phase and the intensities of the S- and P-components... 

Figure 2.58 Schematic representation of the generation of elliptically polarised tight riu the reflect ion of plane-polarised light from a reflective surface.

Figure 2.59 The path followed by the tip of the electric vector of elliptically polarised light. ES, (1 and ,. ref show the directions of the planes of the S-potarised and P-polarised light. For...

Interestingly, the work of Blum et ai (1986) showed that a surface selection rule operates in X-ray reflection absorption. Thus the synchrotron radiation employed in their experiments was polarised in the plane of reflection and the authors noted that bonds perpendicular to the plane of reflection do not contribute to the SEXAFS (cf. the infrared SSR, discussed above). 

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