GB1336777A - Channell plate image intensifier - Google Patents

Abstract

1336777 Image intensifier tubes STANDARD TELEPHONES & CABLES Ltd 28 Oct 1971 50077/71 Heading H1D In a channel plate image intensifier the output of the various channels is equalized by providing between the plate and the phosphor screen a resistive structure having a capacitance low enough to set a maximum to the number of electrons of a bunch which are able to reach and excite the phosphor and a time constant greater than the duration of a bunch of electrons produced by a single primary electron. In one arrangement, Fig. 1 (not shown), the phosphor screen is provided with a resistive backing which is preferably of carbon. In another arrangement, Fig. 2 (not shown), a resistive membrane is located 10 microns from the output face of the channel plate; the membrane may be of vitreous carbon obtained by pyrolizing a porous plastics membrane, or alternatively of silicon, woven carbon fibre, or a glass fibre with an evaporated resistive coating. If the duration of a bunch of electrons from a single primary electron is 2 Î 10<SP>-10</SP> seconds, a suitable time constant is about 10<SP>-9</SP> seconds, and a suitable resistance of the backing layer or membrane would be about 2 Î 10<SP>6</SP> ohms per square. In a further arrangement there are two successive channel plates, the second being thinner than the first and having its channels treated with carbon or heavily oxidized manganese glass to provide a low secondary emission ratio; only one electrical connection is made to the second channel plate, and that is made to a high resistance layer on its input face. Another type of tube, Fig. 3 (not shown), uses a screen wherein the phosphor is located at the bottom of an array of blind holes. This array may be provided by etching a fibre optic plate to provide an array of blind holes 5 microns in diameter and 10 microns deep in which the phosphor is deposited. Aluminium is evaporated normally over the phosphor and over the front of the screen, the thin coating deposited on the side walls being made non-conductive by a slight oxidation which does not affect the conductivity of the other layers. Finally, high resistivity material such as germanium is evaporated obliquely to provide the high resistance connection (5 x 10<SP>7</SP> ohms) required between the two layers.