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As mentioned in other NVI, papers given this session, faceplate development was con-cluded quite a while ago and recent measure-ments on current faceplates are scarce. It was also mentioned that a problem area has recently been uncovered concerning the input or cathode faceplate of an inverter or wafer tube. This discussion will deal with the nature and extent of this problem including recent test data bearing on the problem. To adequately discuss this, a review of the function of a faceplate would be in order. Figure 1 shows the objective lens, faceplate, and photocathode as employed in Night Vision Systems. The fiber optic faceplate's primary function, and the one in which we are interested, is to transfer an image formed on the input face of the plate through the thickness of the plate to the photocathode, which is deposited on the output face of the faceplate. If the transfer process degrades the image, the photocathode starts off with a blurred and low contrast image. To this are added or multiplied other system degradation factors and the final image is then definitely not state-of-the-art. To achieve a good image transfer through the fiber optics plate, stray light, which spills out of each fiber or which initially fell between the fiber core areas, must be taken care of. To do this, the industry developed various methods of placing black glass around the fibers or between the fibers. This black glass was to absorb any stray light which was wandering about outside the fiber walls, which lead to the name EMA, or "extra mural absorption." This black glass, EMA, or interstitial opaque coating as it is sometimes called, then is somehow interspersed throughout the plate and outside of the fiber cladding to absorb much of the stray light formed by imprefections which serve as scatter centers in the fibers, by light entering at too great an angle for the total internal reflection necessary for propagation down the fiber, or by the incident light falling outside of the fiber core cross section.
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