Electro-optical cell

Note In the off-state the electro-optical cell contains a thin film of a nematic liquid-crystal with mutually perpendicular directors at the upper and lower glass plates hence to reach the on-state the director performs a 90° twist over the thickness of the liquid crystal film. 

There is another way to obtain giant laser pulses of a few ns duration, known as active Q-switching. The shutter is an electro-optical cell which is triggered at some preset time after the pump flash. These electro-optical shutters are Kerr cells or Pockels cells. 

Active Q-switching occurs when laser light access to one of the mirrors in the cavity is controlled electro-optical cell, which works on the principle of affecting the passage of polarized light (see... 

Instrumental specifications for specular reflection spectroscopy have been reviewed in detail by McIntyre (1973a). Typical apparatus, electro-optical cells, and electrodes for specular reflection spectroscopy and measurement procedures used in the spectroscopy are described in this section. 

Fig. 10. Optical system of apparatus for specular reflection spectroscopy LS, light source M5, semitransparent mirror 02, polarizer PM, and PM, photomultipliers G, grating A, bar for changing the incidental angle W, working electrode R, reference electrode, C, counter electrode , electro-optical cell. (From Kusu and Takamura, 1985b, with permission.)...

It can be seen clearly from Fig. 15 that MSFLC cells offer many advantages. For example, a large gap of 10 Xm can be used [109, 130] instead of 2 pm used in SSFLC cells [131]. The polymeric nature of the LC materials offers excellent shock resistance and mechanical stability. No rubbing of the substrate is needed. We believe that practically useful electro-optical cells can be made utilizing this concept if the FLC-coil diblock copolymers are properly designed, synthesized, and processed. 

The electro-optical measurements were carried out using an electro-optical cell described by Talroze, et al. which was mounted on a heating stage of a polarizing microscope, MIN-8. A photo-element was used in conjunction with a recorder to monitor the transmitted light intensity. The film thickness was about 12 pm, electric field intensity was 10 V/cm. The pleochroic dye for studying the guest host effect had an absorption band at 505 nm. 

The decrease of the orientation rate with the decrease of temperature seems to be related to the increase of the viscosity of the LC melt. The absence of the initial homogeneous orientation of the polymeric liquid crystal in the electro-optical cell implies that the average viscosity of the LC polymer is the important factor, instead of the rotational viscosity. 

As mentioned, the electric field induces the orientation of polymer side groups. The homeotropic structure with an alignment of these groups (Ae > 0) normal to the electro-optical cell areas is thus formed. The possibi>... 

Fig. 2. Schematic drawing of the measuring arrangement for thermo-recording 1-laser, 2-attenuator, 3-focused lens, 4-electro-optical cell, 5-a.c. voltage generator. ...

The times for a twisted nematic electro-optic cell to switch on or rise (tr) or to switch off or decay (t[Pg.313]

In an extensive work on polysiloxane polymer liquid crystals, Finkelmann et al. examined their performance in a twisted nematic electro-optical cell. In parallel with the polymer measurements, analogous studies were carried out on low molar mass nematic compounds of equivalent dielectric anisotropy (Ae). Both the low molar mass nematic materials and the polymer side-group moieties were mixtures of methoxy- (or alkyloxy-) and chlorine-terminated benzoate esters. Cells were prepared using rubbed polyimides and in the polymer case the samples were annealed for several hours to obtain defect-free aligned textures. Measurement of the threshold voltages, for both the low molar mass compounds and the polymer, showed ... 

Other authors used different mathematical procedures which provided practically analytical solutions in the specific case of light propagation in cholesterics. The significance of the Berreman-Scheffer method lies in the fact that it can be applied to any system in which the director changes only along one direction (stratified medium). This occurs for instance in liquid-crystalline electro-optic cells, hence the method is of importance in device applications also. Furthermore Its extension to biaxial or absorbing media is straightforward thus it can be employed for smectic C or dyed films too. 

Fig. 20. Schematic drawing of an electro-optical cell using conducting polymers [354]...

Either, or both, excitation source modulation frequency or detector response can limit instrument capabilities. Most standard commercial instruments have modulation frequencies up to a maximum of a few hundred MHz and are best suited for relatively long-lived fluorophores with high quantum yields. The excitation source is typically a modulated LED or laser diode, or for a wide wavelength range, light from a continuum steady-state source, such as a Xe arc lamp modulated with an electro-optical cell, such as a Pockels cell detection is typically a fast photomultiplier, or multichannel plate photomultiplier. Polarisers are commonly used accessories. Such an instrument is ideally suited for lifetimes of a few ns, but will also measure, albeit with lower precision, lifetimes in range of lOO s ps. GHz modulation frequencies are obtained with mode locked lasers with a fast multichannel plate photomultiplier and these allow lifetime measurements in the range of tens of ps. 

Typical electro-optical cells consist of (i) an electrically conductive indium tin oxide (ITO) glass as electrode, (ii) a thin film of the electrochromic polymer in the electrolyte (e.g. lithium perchlorate in acetonitrile), and (iii) hold by a spacer a nickel gauze on a back glass plate [179]. 

Electro-optical cell for field effect type liquid crystal display, USP3,994,567 (1974)... 

---