Light Valves

Ultraschali, m. (Physics) auperaonant. -welle, /. supersonic wave, -zelle, /. supersonic light valve. 

The EPID concept can be combined with other developments in imaging technology to produce optical devices such as light valves and x-ray imagers. The accompanying illustration shows an example of an electrophoretic x-ray imager. 

Changes in display status should signify changes in functional status rather than simply indicate a control has been activated, for example, a lighted VALVE CLOSED indicator should signify that the valve is actually closed, not that the VALVE CLOSED control has been activated. 

Useful applications have been found lor the varied effects of these crystal changes. One of the first came from the properly of selectively reflecting visible light because this is lempcraiurv-dependent. the property can be used as a temperature detector, and in gel lurm liquid crystals have been used lor the early detection of those cancers which cause hot spots in the body. Applications of the smectic modifications arise from their ferroelectric properties this phase can function as a fast-switching light-valve device with memory. This kind of application requires some... 

The advantages of SSFLC devices derive to a large extent from the spontaneous macroscopic polarization P of the phase. For example the electrooptic rise time of a prototypical SSFLC light valve is inversely proportional to the magnitude of the polarization. In order to design new FLC materials with large P in a directed way, we... 

Microstructures and systems are typically fabricated from rigid materials, such as crystalline silicon, amorphous silicon, glass, quartz, metals and organic polymers. Elastomeric materials can be used in applications where rigidity is a drawback. We have demonstrated the concepts of elastomeric systems by fabrication of photothermal detectors, optical modulators and light valves. We believe that elastomeric materials will find additional applications in the areas of optical systems, micro analytical systems, biomaterials and biosensors. 

Several experiences of severe weeping from valve trays have been reported (1,71,75). A well-designed valve tray is unlikely to have too many valves, but trays with light valves are common in an effort to reduce pressure drop. To avoid the turndown problems, manufacturers often specify a valve tray with two valve weights (Fig. 6.19e). When the light valves open, the heavy ones are still shut, which reduces the ratio of slot to active area and avoids weeping. This practice is discussed in detail elsewhere (1,71). 

Very light valve train utilizing low spring pressure valve springs and low friction components (roller rockers and lifters). 

When the liquid flow path is relatively short (< 30 in), the row of valves closest to the tray inlet should contain light valves. If the inlet row contains the heavy valves, aeration at tumed-down conditions may not begin until some distance into the tray. This shortens the effective flow path and may lower tray efficiency. 

Linear materials are used primarily for high-speed modulation of the intensity, amplitude, phase, frequency, or direction of a light beam. Quadratic materials are used principally for light valves and shutters. 

Novel, flexible, completely organic, polymer dispersed liquid crystal (PDLC) "light valves" were fabricated using two flat pieces of commercial overhead transparency substrates (Nashua j -20) coated with polypyrrole between which a film of commercial PDLC material (Norland Products Co. NOA 65 optical adhesive and BDH Ltd. E7 liquid crystal fluid together with EM. Ind. 15 micron polystyrene spacers) was sandwiched. The optical adhesive was polymerized by exposure to UV light. Thin conducting polypyrrole films of varying controllable thickness were deposited on the overhead transparency. 

A transmissive liquid crystal display (LCD) that is sometimes referred to as an LCD light valve... 

MLCs also have their place in optical applications, mainly as so-called polymer-dispersed LCs (PDLCs). A PDLC constitutes a microemulsion of an MLC in a film of a conventional (nonPLC) polymer. In the switched off state the MLC and the polymer have different refractive indices, dispersed MLC droplets (not unlike to the islands in PLCs) scatter light quite effectively, and the film is opaque. Then an external electric field is applied, for instance across a capacitor-like metal coating on both sides of the film. The director in all MLC droplets becomes the same. One can choose the MLC + polymer pair so that the refractive index along the director is the same as that of the host polymer. In that case the film in the electric field becomes transparent. Switching the field off and on, one has a light valve with a fairly large area. 

In this paper a laser beam addressed liquid-crystal light valve is described. Its writing speed is limited by the available laser power and by the laser scanning system, but it does have selective erase capability. This feature, which allows local erase and update of information on the screen, is important in large storage displays and is not available with present storage CRT s. 

To achieve an effective turndown operation, a manufacturer usually specifies two valve weights. When light valves open, the heavy ones still close, which reduces the active bubble area and thus avoids weeping. Furthermore, weeping usually occurs at the exit of the downcomer apron area. Thus, it is critical to maintain the level of the tray. 

J. Grinberg, W. P. Bleha, A. D. Jacobson, et al., Photoactivated birefringence Uquid crystal light valve for color symbology display, IEEE Trans. Electron Devices ED-22, 775 (1975). 

P. S. Drzaic, Polymer dispersed nematic liquid crystal for large area displays and light valves, J. Appl Phys. 60, 2142 (1986). 

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