Polarization light

There is a fiirtlier item of infonnation in this procedure. If one of the tln-ee component integrals is non-zero, the molecule will absorb light polarized along the correspondmg axis. For example, if p,. = f dris... 

The n ==> n transition thus involves ground Ai) and exeited Ai) states whose direet produet (Ai x Ai) is of Ai symmetry. This transition thus requires that the eleetrie dipole operator possess a eomponent of Ai symmetry. A glanee at the C2v point group s eharaeter table shows that the moleeular z-axis is of A symmetry. Thus, if the light s eleetrie field has a non-zero eomponent along the C2 symmetry axis (the moleeule s z-axis), the n ==> 71 transition is predieted to be allowed. Light polarized along either of the moleeule s other two axes eannot induee this transition. 

Fig. 17. Polymer dispersed Hquid crystal display (PDLC). (a) U < clear state, where U) is the threshold voltage of the ceU. and rij represent the indexes of refraction for light polarized parallel and perpendicular to the director of the Hquid crystal represents the index of refraction of the isotropic...

Optical properties also provide useful stmcture information about the fiber. The orientation of the molecular chains of a fiber can be estimated from differences in the refractive indexes measured with the optical microscope, using light polarized in the parallel and perpendicular directions relative to the fiber axis (46,47). The difference of the principal refractive indexes is called the birefringence, which is illustrated with typical fiber examples as foUows. Birefringence is used to monitor the orientation of nylon filament in melt spinning (48). 

Both the chemical solubility and the electrical properties are consistent with those expected of a lightly polar polymer, whilst reactivity is consistent with that of a polymer containing hydrolysable carbonate ester linkages partially protected by aromatic hydrocarbon groupings. The influence of these factors on specific properties is amplified in subsequent sections. 

The electrical insulation characteristics of bis-phenol. A polycarbonates are in line with those to be expected of a lightly polar polymer (see Chapter 6). 

Being only lightly polar and well below the Tg at common ambient temperatures the polymer is an excellent electrical insulator even at high frequencies. ... 

When light that has experienced such retardation is viewed by a polarizer oriented at 90° to the original plane of light polarization, the two components of the original light beam interfere with one another. This results in a change in color and intensity of the observed light. Observed colors correspond to different levels of retardation at that point, which in turn correspond to stress levels. 

Fig. 8. Dichroism of electronic absorption spectra of oriented and nonoriented PAN films after IR irradiation, (a) Dependence of optical density ( >) on the wavelength for various values of (angle between film orientation axis and light polarization plane).

Pulsed method. Using a pulsed or modulated excitation light source instead of constant illumination allows investigation of the time dependence of emission polarization. In the case of pulsed excitation, the measured quantity is the time decay of fluorescent emission polarized parallel and perpendicular to the excitation plane of polarization. Emitted light polarized parallel to the excitation plane decays faster than the excited state lifetime because the molecule is rotating its emission dipole away from the polarization plane of measurement. Emitted light polarized perpendicular to the excitation plane decays more slowly because the emission dipole moment is rotating towards the plane of measurement. 

The p indicates symmetry-antisymmetry of the Legendre coefficient with respect to a light polarization switch, E indicates the response to an enantiomer switch. 

The problem of solvent absorption can be overcome by measuring the change in reflectivity of the electrode either by (a) modulating the state of light polarization between p-polarized and s-polarized radiation, or (b) using p-polarized radiation and taking spectra at two different electrode potentials. 

Aa is the absorbance in the tilted geometry, Az the absorbance measured in normal incidence geometry with light polarized along the Z-axis, and n the refractive index of the sample. The isotropic refractive index in the visible range is often used as a first approximation, but quantitative measurements require knowledge of the anisotropic refractive indices at the wavelength of interest [29]. 

A method of analysis of light polarizing systems. J. opt. Soc. America... 

---