Polariser, rotating

In the Kerr effect, the polarisation rotation can be expressed by a relation similar to Eq. (4.72), except that it is independent of specimen thickness. The Kerr effect can be observed in three geometries polar, longitudinal and transverse, shown in Fig. 4.68. The rotation angle is largest in the polar geometry, where magnetisation is perpendicular to the specimen surface. 

Therefore, the simplest model predicts the existence of one maximum of selective reflection centered at the wavelength = n)Po and the circular polarisation of the reflected beam. However, the spectral dependence of the selective reflection and the magnitude of the angle of the light polarisation rotation by the cholesteric structure can only be discussed by analysing the Maxwell equations for the optical waves propagating in the periodic medium. 

Figure 1. shows the measured phase differenee derived using equation (6). A close match between the three sets of data points can be seen. Small jumps in the phase delay at 5tt, 3tt and most noticeably at tt are the result of the mathematical analysis used. As the cell is rotated such that tlie optical axis of the crystal structure runs parallel to the angle of polarisation, the cell acts as a phase-only modulator, and the voltage induced refractive index change no longer provides rotation of polarisation. This is desirable as ultimately the device is to be introduced to an interferometer, and any differing polarisations induced in the beams of such a device results in lower intensity modulation. 

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.

Next we show the Raman intensity of the (10, 10) armehair CNT as a function of sample orientation (see Fig. 3). Here we rotate the CNT axis from the z axis by fixing the polarisation veetors to lie along the z and x axes, respeetively for the V and H polarisations. In this geometry, three rotations of the CNT axis are possible for the VV and the VH eonfigurations, and these three rotations are denoted by 0,- (i = I, 2, 3). Here 0] and 02 are the angles of the CNT axis from the z axis to the x and y axes, respeetively, while 03 is the angle of the CNT axis around the z axis from the x to the y axis. Sinee we put the horizontal... 

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. 

The angle of rotation is, of course, directly proportional to the thickness of the layer of active substance through which the polarised light passes. The expression optical rotation or rotatory power is universally understood to be the observed angle of rotation produced by a column of 100 mm. of the optically active substance. If tubes of other lengths be... 

Zembura has made specific use of the rotating disc for investigation of the effect of flow on corrosion reactions. This work has shown that it is possible to determine the type of control (activation or concentration polarisation) of zinc dissolving in 0.1 N Na2S04 (de-aerated), which followed closely the predicted increase in hydrogen ion reduction as the flow rate increased, and proved that in this example... 

Procedure. Place 25.0 mL of the thiosulphate solution in the titration cell. Set the applied voltage to zero with respect to the S.C.E. after connecting the rotating platinum micro-electrode to the polarising unit. Adjust the range of the micro-ammeter. Titrate with the standard 0.005 M iodine solution in the usual manner. 

Dilute solutions of antimony(III) and arsenic(III) (ca 0.0005M) may be titrated with standard 0.002 M potassium bromate in a supporting electrolyte of 1M hydrochloric acid containing 0.05 M potassium bromide. The two electrodes are a rotating platinum micro-electrode and an S.C.E. the former is polarised to +0.2 volt. A reversed L-type of titration graph is obtained. 

The titrations so far discussed in this chapter have been concerned with the use of a reference electrode (usually S.C.E.), in conjunction with a polarised electrode (dropping mercury electrode or rotating platinum micro-electrode). Titrations may also be performed in a uniformly stirred solution by using two small but similar platinum electrodes to which a small e.m.f. (1-100 millivolts) is applied the end point is usually shown by either the disappearance or the appearance of a current flowing between the two electrodes. For the method to be applicable the only requirement is that a reversible oxidation-reduction system be present either before or after the end point. 

In practice, the emission line is split into three peaks by the magnetic field. The polariser is then used to isolate the central line which measures the absorption Ax, which also includes absorption of radiation by the analyte. The polariser is then rotated and the absorption of the background Aa is measured. The analyte absorption is given by An — Aa. A detailed discussion of the application of the Zeeman effect in atomic absorption is given in Ref. 51. 

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... 

We have also used a non-radiometric-binding approach based on fluorescence polarisation [29], where a fluorescent label is used in place of a radiolabel. As the fluorescently tagged oxytocin binds to the receptor, its rotational velocity is reduced and the polarisation of the fluorophore increases. The displacement of the ligand may be measured by a decrease in polarisation. 

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