| 摘要 |
1,137,669. Image converter tubes. W. HEIMANN. 18 March, 1966 [26 March, 1965; 21 Sept., 1965], No. 12086/66. Heading HID. In an image converter tube in which electrostatic electron lenses are used to form an image of a photocathode, pin-cushion and curvature of field-type distortion is reduced or suppressed by imposing a radially extending potential difference between a small central area and the edge of the surface on which the photo-emissive layer of the photocathode is disposed. This potential difference may be applied by supplying a current to the centre of the photocathode surface and extracting it at its edges using transparent conductive coatings. As shown, a metal ring 2 is provided on a glass support 5 and connected via lead 3 to a battery. A transparent conducting coating 1, e.g. of SnO 2 , is applied to the support 5 within the ring 2. The ring 2 and coating 1 are covered everywhere except over a small central area, which as shown in Fig. 4 may be a serrated region, by a transparent insulating coating 4, e.g. SiO 2 , a further transparent conducting coating 1a, extending to outer metal ring 3 connected to the other battery terminal, being applied over coating 4. The coating la may also support the photo-emissive layer. In another embodiment, Fig. 5 (not shown), a glass support is coated with, successively, a transparent conducting coating, a transparent semi-conducting coating, and a transparent coating having a high resistance whose thickness or homogeneity varies so as to produce a voltage curve that varies quadratically with the radius from the centre to edge. Alternatively, variation in homogeneity of the semiconductor coating may be used to produce the required voltage curve. |
