Patent GB-841200-A (GB)
Title: Improvements in or relating to electronic image forming tubes
Inventor: COURTNEY-PRATT JEOFRY STUART
IPC: H01J29/89
Filed: 1956-09-17
Abstract: 841,200. Cathode-ray tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Aug. 26, 1957 [Sept. 17, 1956], No. 28407/56. Class 39(1). [Also in Group XX] The image-receiving wall of an image-forming tube consists of a bundle of light guiding rods 12, Fig. 2, bonded together by a bonding material in the interstices between the rods so as to form a gas-tight slab with the longitudinal axes of the rods running transversely from one surface of the slab within the tube to another surface of the slab outside the tube, the length of each of the rods in the direction of its longitudinal axis being large in relation to its dimensions in any direction normal to its longitudinal axis, the slab being bonded to the remainder of the envelope 13 in gas-tight fashion so as to form a structural wall of the tube. In the form shown a fluorescent coating 20 on the inner wall is excited by electron beam 15 and the light is transmitted without loss of resolution to a photographic plate 21 placed emulsion side downwards upon the flat outer wall. A preferred application is to image intensifier tubes, particularly for X-rays, having a photo-sensitive coating 26, Fig. 3, and a fluorescent screen on a light-guide slab 27. Further tubes 23, 24 with similar slabs 29, 31 may be cascaded after the first tube 22, these further tubes being provided also with lightguide slabs 28, 30 at the cathode ends. Slab pairs such as 27, 28 may be arranged at random with little loss of resolution but if desired they may be made identical and similarly aligned so that their individual tubes match up. An equivalent single tube form may have two intermediate walls formed as light-guide slabs and carrying fluorescent and photo-electric coatings on opposite faces. Other applications are to electron diffraction cameras, electron microscopes, large radar or television display tubes and high-speed camera tubes. In the latter, a system of tapered guides is used which produces on the photographic plate a series of dots. By slightly displacing the plate a number of frames can be recorded on the same plate and individual frames read off by a suitable mask. The light-guide slab may be made bonding together short lengths of glass filament a few thousandths of an inch in diameter with a glass of low melting point and lower refractive index than that of the rods, or by slicing a coil of such filaments; or by bonding together alternate flat and corrugated strips 33, 32, Fig. 5, of high melting point, low refractive index glass, with a low melting point, high refractive index glass forming the equivalent of a rod in each corrugation; or by assembling ridged sheets 34 ... 39, Fig. 7, with a low melting point, low refractive index glass binder. Where rods are used they may be woven into a fabric with smaller threads forming the warp, to facilitate correct assembly, Figs. 11, 12 (not shown). The passages in the guide may converge or diverge to reduce or enlarge the image, although in the former case there is severe loss of light. It is also possible for tapered guide rods to be arranged in a parallel format, so that a picture thrown on the broad ends is reduced to a series of dots at the narrow ends for the high speed camera application. If the slab is made of non-gas-tight material, such as synthetic resin, a gas-tight coating of glass may be put on the inner wall. The rods may be coated individually with a reflecting metal coating.