Elliptically polarised light

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...

Figure 2JS Schemanc representation of the generation of elliptically polarised light t iu the reflection of piune-polariscd light from a reflective surface.

In order to suppress the formation of elliptically polarised light rather than plane polarised light in a TN-LCD, it is necessary to control the cell thickness, d, and the birefringence of the nematic medium. An, with respect to the wavelength of light in a vacuum, X, according to the equation ... 

Modern CD instrumentation measures the difference in absorbance of right-add left-handed circularly polarised light directly, so CD spectra are often reported as As, with units the same as for s itself. Sometimes, however, for historical reasons, the circular dichroism of a sample is recorded as ellipticity. The origin of the term lies in the fact that if one of the circularly polarised beams emerging from the sample is attenuated relative to the other, on recombination the two circularly polarised beams form elliptically polarised light, not plane polarised light. The ellipticity 0, is tan (Z / ) where b is the minor and a the major axis of the ellipse. The conventional molar ellipticity [9]... 

Figure 3.25 The effect of an anisotropic crystal on initially plane polarised light, producing elliptically polarised light. The number of wavelengths in the crystal has been reduced for clarity.

Fig. 155. Macrophages in the marginal zone of the splenic white pulp of a male white rat (No. 30) 8 weeks after an intravenous application of 25 mg Brazilian crystallised quartz (specific surface 2 mVg). Fixed by immersion in Bouin s fluid. Paraplast. Azan modification using rubine fast rea and aniline blue (Specht 1973). Objective Leitz Pi 40/0.65. Leitz-Orthomat (x3.2). Elliptic polarised light. Agfachrome 50 L professional...

Passing through a quarter wave plate, the elliptically polarised light may be converted to plane polarised light rotated through half the ellipticity angle. This angle can be very accurately determined... 

The effect can be manifest by placing the polymer solution in a suitable cell (Fig. 6 a) between a pair of electrodes. If a beam of well collimated light is passed centrally through this cell, with the light initially linearly polarised at 45° azimuth to the electric field direction, then elliptically polarised light will leave the cell when... 

The anisotropy itself may be linear or circular, or a combination of both. In linear anisotropy the refractive index depends on the direction of polarised light. It is found in solid polymers under tension and in viscous polymeric liquids during flow (shear and elongation). The refractive index can also depend on the chirality of polarised light in this case one speaks of circular or elliptic anisotropy. Thus the so-called "optical activity" is circular birefringence its extinction analogue is circular dichroism. 

The super birefringent effect (SBE-LCD) reported by Scheffer and Nehring from Brown Boveri in Baden, Switzerland, uses the optical interference of two normal, elliptically polarised modes of transmitted light generated by a high-tilt, highly-twisted nematic structure viewed between two polarisers set in an unusual way, i.e. the input polarisation direction is not parallel to the nematic director at either substrate surface and the polarisers are not crossed at 90°, see Figure 3.10. 

A consequence of this is that drcularly polarised light becomes elliptically polarised as two components of differing intensity are combined (Figure 7-16). This effect is called circular dichroism and it is represented by the elliptirity 0, which is defined as... 

Fig. 2. Light initially linearly polarised at 45° to the plane of incidence is elliptically polarised after reflection due to the stepwise changes in the amplitude and phase of both the p and s components of the electric vector.

Therefore the emerging light is elliptically polarised with an orientation given by... 

Ellipsometry was in fact the earliest optical technique to be applied to the study of electrode processes. It involves the determination of the change in polarisation state of an obliquely incident light beam upon specular reflection at a surface. In order to fully define a monochromatic light beam it is necessary, in addition to knowing the frequency, amplitude, and direction of propagation, to include information about the electric and magnetic vectors which describe the polarisation state. Since these vectors are orthogonal and related in amplitude it is, in fact, only necessary to consider one of them, and it is the electric vector that is usually chosen. If this vector lies in a plane then the beam is said to be plane polarized, and further if this plane lies parallel to the plane of incidence at a surface the beam is said to be p-polarised, whereas a beam polarised in a plane perpendicular to the plane of incidence is referred to as s-polarised. For any beam it is possible to resolve the electric vector into its s and p components, and when these components are of the same frequency but different phase and amplitude the beam is said to be elliptically polarised. This name arises from the... 

Fig. 1. The electric vector of light passing through a bi-refringent material, with n, = 1.10 and ny = 1.15. The light is initially polarised at 45° to the x,y directions. The two perspective views show the progressive induction of ellipticity within the material.

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