Electro-optic Shutters and Filters

The psychologist and the visual scientist often need a rapid and silent means of interrupting or attenuating light. By using fluorescent lamps, glow-modulator tubes, light-emitting diodes, electroluminescent panels or cathode-ray tubes, it is sometimes feasible to modulate the light source : but often, because the light must be very intense or because particular spectral bands are required or because the stimulus is complex or naturalistic, an independent shutter or filter is needed. Mechanical shutters may not offer the requisite speed or silence; and their vibration may disturb other optical components, such as pellicles. An opaque vane, or a very small mirror, mounted on a galvanometer or a stepping motor, may be fast and almost noiseless, but can be used only when the aperture is small (in a Maxwellianview system, for example, where small images of the light source are formed). In the hope of finding a further solution to this recurrent and very general problem, we have examined the potential of materials of the class known as liquid crystals. The optical properties of some of these materials may be altered by the application of electric fields. We describe the principles, the advantages, and the limitations of liquid crystal devices, and offer a guide to their use.