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Publisher Summary This chapter studies modulation-transfer function and background of various image-intensifier output screens. The intensity distribution of the photoelectrons of an electronoptical image intensifier is transformed into a visible image by the output screen. The quality of this transformation depends on numerous properties of this screen. The modulation-transfer function (mtf) describes the loss of contrast resulting when details of different size are transmitted. The term background refers to the increase in brightness of an image element in the center of the screen, which takes place if the diameter of the exciting beam is enlarged. Several disturbing processes, such as light conduction in the substrate and electron scattering, cause this increase in brightness. The interrelations among screen composition, method of manufacture, and quality characteristics of output screens are rather complex. The background can be reduced by (l) use of very thin and light absorbing substrates such as polyimide or mica; (2) reduction of the binder content of the phosphor; and (3) use of deposition methods that result in a low degree of optical contact between phosphor and substrate, such as the rotational coating method. |
