Polarizers/Polarization contrast ratio

The measurements were carried out with various laser peak intensities, pulse durations and contrast ratios. We used a half-wave plate and two polarizers to change the laser energy. The original position of the grating, which gives a 30-fs pulse, was determined with high accuracy from ionization rates... 

In Fig. 2 we show the dependence of azimuthal angle (pmpolarization conversion takes place on the angle of incidence for different ratios of dielectric constants 2 / i It is seen that

contrast ratio. The value of max 5° at 0=0 is also independent of a particular profile of electron density distribution in 2D system as well as the modulation factor Ans= NA N )l(NA+N ). At 0 O the value of is smaller than 45°. A smaller contrast ratio corresponds fo smaller (p max- The value of

total reflection angle 0-0r because, in this case, the in-plane component of electric field in the plane of 2D electron system vanishes. 

Also, a thermally induced phase separation of hq-uid crystals and PVK occurs [72], Multiple domains of the disordered liquid crystals can scatter incident light. Applications are hght shutters, with the advantages of low driving voltage, polarization-independent scattering, fast response, and high contrast ratio. 

The tradeoff between angular viewing dependence and N is shown explicitly in Fig. 2 where measured contrast ratio is plotted as a function of the angle of incidence 0 in the principal viewing plane for a typical TN-LCD with E-7 biphenyl liquid crystal mixture between crossed polarizers. The principal viewing plane is defined by the sample normal and the liquid crystal director midway between the cell electrodes. Contrast ratio is defined as the ratio of cell transmission I with Vjjg applied to transmission with V3 applied. 

Fig. 2, Tradeoff between angular viewing dependence and number of multiplexed lines N. Plots are for contrast ratio versus angle of incidence 0 in principal viewing plane. Widest field of view is for low N. Polarizer alignment normal to the nematic director (n) at the adjacent LC surface emphasizes the double lobe for N=2 as discussed in the accompanying paper. ...

In the limiting case of high voltage applied to a "perfect" cell between crossed polars, the transmittance should be dictated by the dichroism of the polars. Defining dichroism of a polar as the difference between absorbances of the polar in crossed and parallel orientations to a perfectly polarized beam, it should be apparent that polar dichroism would have to be somewhat greater than 5 to achieve a contrast ratio of 10 under the above conditions. Literature on commercially available polars does... 

As shown in Figure 8.24, with film compensation the 100 1 contrast ratio barely exceeds 75° polar angle. This viewing angle performance is not as good as that of the IPS-LCDs described in Section 8.5. This is due to the fact that the intermediate states, points E and F, are not located on the great circle that passes through S2 and S3 axes. 

In the abovementioned two absorption-type transflective LCDs, only one polarizer is employed instead of two. Therefore, the overall image in both T- and R-modes is relatively bright. However, due to the hmited dichroic ratio of the employed dye molecules (DR 15 1), a typical contrast ratio of the guest-host LCD is around 5 1, which is inadequate for high-end full color LCD applications [29]. Thus, the absorption-type transflective LCDs only occupy a small portion of the handheld LCD market. 

Consider a (0°, iso ll bistable TN where the entrance polarizer is at 45° with respect to the hquid crystal at the entrance plane and the exit polarizer is at -45° with respect to the hquid crystal at the entrance plane. Find the three values of the retardation with which the display has contrast ratios. Give the transmittances of the bright and dark states under those retardation values. 

Most of the LC devices operate under a linearly polarized light in order to achieve high contrast ratio. The use of a polarizer reduces the optical efficiency dramatically. The maximum transmittance of a pair of polarizers is only about 38%. Polarization-independent LC devices for phase or amplitude modulation are highly desirable. 

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