US2172728A

US2172728A - Electron discharge device

Info

Publication number: US2172728A
Authority: US
Publication date: 1939-09-12
Anticipated expiration: 1956-09-12

Description

Sept. 12, 1939, Uc 2,172,728

ELECTRON DISCHARGE DEVI CE Filed March 31, 1938 INVENTOR E. BRUCHE ATTORNEY Patented Sept. 12, 1939 PATENT OFFICE ELECTRON DISCHARGE DEVICE Ernst Briiche, Berlin-Reinickendorf, Germany,

assignor to General Electric Company, a corporation of New York Application March 31, 1938, Serial No. 199,162 In Germany November 26, 1936 6 Claims.

In connection with picture scanning or dissection in transmitting television pictures it has become more and more general practice to utilize an arrangement which, basically, may be traced back to that disclosed by Dieckmann and Hell in German Patent No. 450,187. The optical picture or pattern to be transmitted is projected or focused 'upon a layer or coating responsive to luminous actions, and the photo-electrons released from 10 this layer according to the intensity of the impacting or incident light are accelerated towards an anode mounted opposite the photo-cathode. In the anode is a tiny scanning hole posteriorly of which is mounted a cage designed to catch or 1B collect the incoming electrons and to evaluate them. By deflecting the photo electron stream in two directions at right angles to each other it is possible to make conditions so that consecutively the electrons issued by each point or reduced area of the cathode reach the cage with the result that scanning of the picture is accomplished.

This scheme is not as satisfactory as would be desired for the reason that the electrons released from a unit or point of the photo-cathode, as a result of their velocity and direction of emergence, disperse or scatter with the consequence that to a given point on the photo-cathode there will correspond a more or less large areaon the anode or the plane of the collector cage. For this reason, means were provided to prevent this action by focusing the electrons to cause them to travel rectilinearly to the anode. Such means included a homogeneous magnetic field positioned at right angles to the cathode as shown in the British patent to Triggs No. 368,721. In an arrangement of this nature, the electrons issuing at right angles from the planar photo-cathode travel along rectilinear paths, whereas the electrons which issue obliquely from a given point move along helical paths around the straight path starting at the same point. What thus results upon a collector or gathering anode which is also planar is a non-enlarged erect pattern or image.

Now, for the purposes of picture scanning in television, and also for the use of such an arrangement as an optical equalizing or similar means, it is necessary to deflect the photo-electron stream in one direction or in two directions at right angles to each other. Inasmuch as corresponding points of cathode and anode are connected with one another by practically rectilinear electron paths, the distance of the deflector elements from each other must be at least as great as the diameter of the pattern of the cathode.

This requirement alone almost precludes all chances of satisfactorily using electrostatic deflector means, while in the case of magnetic deflection the inevitable lack of homogeneousness of the field impairs the quality or fidelity of the 5 electron pattern upon the anode.

Now, according to this invention, in arrangements in which an optical or light image or picture is converted or transduced into an electron pattern, short imaging means (lenses) are em- 10 ployed, while the deflector arrangement or arrangements are accommodated within a space of constant or stable electrical potential, to be more precise, at a point where the electron ray path presents a reduced cross-sectional area. 15

The invention is predicated upon a proper appreciation of the fact that in arrangements which comprise short lenses, and with which, therefore, an inverted and generally enlarged image is obtained, which, moreover, is turned where mag- 20 netic imaging is used, a point will arise in the electro-optical system of the imaging device which presents a minimum pencil cross-section. The size of this spot or focus is dependent on the focal distance of the lens, the speed of emer- 25 gence of the electrons from the cathode, and the applied acceleration potential. But it is not dependent upon the size of the optical image upon the cathode. If the focal point or point of electron cross-over is at a place where no elec- 30 trical field prevails, then, according to this invention deflection may be conveniently produced at that place or region. Otherwise, in order that disturbances of the imaging field may be avoided-for such disturbances are extremely unde- 5 sirable-the deflecting means must be mounted at some other place, that is, a place which generally is remoter from the cathode. In case the imaging or focusing is effected by magnetic means and the deflection is accomplished elec- 4o trostatically, deflection could very well be effected inside a space permeated by the magnetic field, provided that the deflector plates consist of nonmagnetic material.

Now, the invention shall be explained in more 45 detail by reference to the drawing in which Figures l and 2 represent different embodiments of the arrangement predicated upon the basic idea of the invention.

Referring to the drawing, Figure 1 shows a 50 glass or ceramic envelope in inside of which is positioned a photo-cathode H. This photocathode may be coated on the end wall of the envelope or may be positioned on a separate electrode. Furthermore the photo-cathode may 55 be planar or curved as shown in the figure. It is upon this photo-cathode that the optical picture to be transmitted or televised is projected or focused, the projection being in the direction of the arrow I 2. An electro-optical imaging or focusing means 13 is provided, the shape and potential of the electrode [3 being such as to produce a short focal length electronic lens. As shown, electrostatic focusing is utilized, althou h so far as this invention is concerned, either electrostatic or electromagnetic focusing may be used or any form or combination of these means.

At the other end of the tube or envelope is provided an anode It for accelerating the photoelectrons and upon which the electron image is focused. This anode may be maintained at a proper potential in order to accelerate the photoelectrons through the tube. Positioned centrally with respect to the anode is a single perforation behind which is positioned a collector anode IS, the collector anode being surrounded by a cage IS. The path of the photo-electrons is indicated by the lines I5 and it may be seen from the drawing that the focusing electrode l3 causes the photo-electrons to cross at the region H5 which is relatively restricted in diameter or crosssectional area. The image which is focused upon the anode M' by reason of the electro-optical means, is of course inverted.

In order to cause deflection of the electron image to produce scanning, deflecting means are provided and for this purpose a pair of deflecting plates [1 are shown. For bi-lateral deflection, a second pair of deflecting plates would of course be provided, the second pair of plates being positioned at right angles to the axis of the plates ll. When proper deflecting voltages are applied to the deflecting plates, the electron image is caused to move with respect to the anode I4, and in so doing elementary points of the image are brought in registry with the opening in the center of the anode. Photo-electrons which originate at the photo-cathode II are therefore permitted to pass through the opening and are collected by the collector anode 39. When the electron image is deflected both horizontally and vertically a series of television picture signals may be derived from the collector anode l9.

Figure 2 is a modification of Figure 1 and shows the use of magnetic deflection in place of electrostatic. The shape of the envelope is somewhat altered in order that the electro-magnetic deflection coils may be positioned exteriorly with respect thereto and furthermore, the focusing electrode 23 may be positioned on the inside surface of a portion of the glass envelope provided the envelope is properly shaped. In operation, Figure 2 is the same as Figure 1 except that the electron image is deflected. electromagnetically instead of electrostatically. In this figure, as in Figure l, for bi-lateral deflection a second pair of deflecting coils would of course be provided, the coils being positioned at right angles to the axis of coils 27. For the purpose of clarity these coils are not shown in the figure.

In each instance regardless of whether electrostatic or electromagnetic deflection is used, it will be noticed that the deflecting means is positioned at the point of cross-over, that is, at the point where the electron stream is of minimum cross-sectional area. By so positioning the deflecting means the electron image may be more accurately deflected with the result that less distortion is present in the television picture signal series. Furthermore, in view of. the fact that the deflecting plates or pole pieces may be positioned more closely together, smaller deflecting potentials may be used. It will be observed that the deflecting plates I! of Figure 1 are curved, the curvature being substantially identical with the curvature of the electron stream at the point where the electrostatic deflecting plates are positioned. This same curvature may also be used in the pole pieces where electromagnetic focusing is employed.

It is conceivable that a combination of electrostatic and electromagnetic deflection may be used in which case the pole pieces of the electromagnetic deflecting means could be used as the electrostatic plates for deflecting the beam in a direction transverse to the direction of deflection as caused by the electromagnetic means.

Various modifications and alterations may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be considered as within the purview of the present invention except as limited by the hereinafter appended claims.

I claim:

1. An electron discharge device comprising an envelope, a surface at one end of the envelope for producing a stream of photo-electrons when a light image is projected thereon, a target anode electrode positioned at the other end of the envelope, electron lens means for focusing the photo-electrons into an inverted image in the plane of. said anode by causing the stream of electrons to converge and cross-over, and electromagnetic electron deflecting means positioned in a plane normal to the axis of the tube and including the cross-over point of the focussed electron stream whereby deflection of the electron stream as a result of energization of the deflecting means is effective only at the region of beam cross-over.

2. An electron discharge device comprising an envelope, a surface at one end of the envelope for producing a stream of photo-electrons when a light image is projected thereon, an anode electrode surface positioned at the other end of the envelope, an electron lens for focussing the photo-electrons into an electron image in the plane of said anode, the electron stream containing at least one electron cross-over point of materially reduced cross-sectional area common to all of the electrons of. the stream, and means for deflecting the electrons in a direction normal to the axis of the tube, said means being positioned at the point of maximum constriction of the electron stream and effective within the region of electron cross-over.

3. An electron discharge device comprising an envelope, a light responsive area at one end of the envelope for producing photo-electrons when a light image is projected therein, an anode electrode surface positioned at the other end of the envelope, electron lens means for focusing the photo-electrons into an inverted electron image in the plane of the anode to thereby create an electron cross-over point of reduced cross-sectional area intermediate the light responsive area and the anode, and electron deflection means positioned adjacent the cross-over point on the focused electron stream whereby the region of beam deflection is substantially restricted to the point of cross-over.

4. An electron discharge device comprising an envelope, a light responsive area at one end of the envelope for producing a stream of photoelectrons when a light image is projected thereon, an anode electrode surface positioned at the other end of the envelope, electron lens means for focusing the photo-electrons into an inverted electron image in the plane of the anode to thereby create a common cross-over point of reduced cross-section for all of the electrons of the stream, and electron deflecting means positioned adjacent the point of minimum cross-section along the electron stream whereby the deflecting means is effective only at the region of minimum cross-section.

5. An electron discharge device comprising an envelope, a light responsive area at one end of the envelope for producing a stream of photoelectrons when a light image is projected thereon, an anode electrode surface positioned at the other end of the envelope, electron lens means for causing a convergence and cross-over of all of the electrons of the stream and for focusing the photo-electrons into an inverted electron image in the plane of the anode, and electron deflecting means positioned adjacent the point of maximum constriction of the electron stream whereby the direction of movement of the electron stream as affected by said deflecting means is restricted to the point of maximum constriction.

6. An electron discharge device comprising an envelope, a light responsive surface at one end of the envelope for producing a stream of photoelectrons when a light image is projected thereon, an anode electrode positioned at the other end of the envelope, electrostatic electron lens means for focusing the photoelectrons into an inverted electron image in the plane of said anode, and electrostatic electron deflecting means positioned at the crossover point of the focused electron stream, said deflecting means including a pair of plates curved to conform with the envelope on the focused electron stream at the region of crossover.

ERNST BRiicHE.