US2189321A - Electro-optical device - Google Patents

Description

Feb. 6, 1940. G. A. MORTQN 2,189,321

ELECTRO-OPTICAL DEVICE' Original Filed Dec. 24, 1955 George JVIorIon A the like.

mensa Feb. s, 194e zusam momo-omen. nEvrcE A. Morton, Audubon, N. J.. assignor to Radio Corporation of America, a corporation c! Delaware substituted for abandoned application Serial No. 55,957, December 24, 1935. This application March 4, 1937, Serial No. 128,976. In France October 28, 1936 5 Claims.

I This application is based on application'Serial No. 55,957, iilecll December 24, 1935 and is a substitute therefor.

This invention relates to electro-optical devices and particularly to improvements in electron-lens systems for electron-telescopes and It is known to those skilled in the art to which this invention appertains that electrons may be vsubjected to a focusing action similar to that achieved in optics with ordinary lens systems. Electron focusing may be produced by subjecting the electrons in their travel to the influence of an electro-static iield or ilelds whereby their trajectories are altered.

An electron-lens may be constituted, for example, by a bi-part conduit or cylinder of uniform cross-section through which the electrons travel from their source to their target or terminal electrode. The foptical center of such a lens is adjacent the space intermediate the cylinder sections.

As described in copending application Serial No. 46,644 to George A. Morton, illed October 25, 1935, when the hollow conduit members are properly proportioned, a sharp image of unity magniilcation may be achieved in accordance with the general formula where m is magnification, v is the distance from the optical center of the lens to the target and u is the distance from the optical center` to the electron source.

Substantially, the same general formula holds true Where, as in certain electro-optical devices, a series of ring-like electrodes are substituted for onel of the cylinder sections for the purpose of rendering the focus of the lens electrically adjustable. Such an arrangement is described in connection with Fig. 2, copending application Serial No. 38,380 to Leslie E. Flory and George A. Morton, filed August 29, 1935.

An object of the present invention is to provide an electro-optical system wherein magnification may be equal to, greater than, or less than unity irrespective ofthe exact length of the members constituting the electro-optical system.

Another object of the invention is to standardize the construction of electron telescopes and the like whereby parts of standard dimensions may be employed in electro-optical devices designed to exhibit dierent xed ratios of magnication.

`that of the other apertured electron-directing Another object of the invention is to reduce the voltage diierence necessary between elements of an electron lens.

Another object is to provide an electron lens structure capable of removing, or otherwise obviating the effects of', stray electrons.

The above and other objects are accomplished in accordance with the present invention by providing the device with an electron-lens constituted by a pair of spaced-apart electrodes having each an oriilce of a diameter less than members. l

1f these orifices are of unequal diameter, the magnification ratio will be other than that dictated bythe physical length of the system: the actual ratio depending primarily upon the relative arrangement of the lens elements. This phenomenon obtains by reason of the different distribution and the different radii of curvature assumed by the equipotential lines of force about' the lens elements. i

If the oriiices are of similar diameter, the voltage difference necessary to achieve a desired ratio of magnification is less than that required in electro-optical systems wherein all of the apertured elements are of the same diameter. With a pair of similar oriiices of reduced diameter, a smaller voltage difference may be employed to maintain a symmetrical distribution of electro- 3 static lines of force since the area embraced by the field is smaller.

While the invention will be disclosed as embodied in an electron-telescope, it is not to be limited by such application as the disclosure in this respect is merely illustrative for purposes of explaining the inventive concept.

Figure l' is a diagrammatic sectional view of an electron telescope embodying an electron-lens Within the invention; the diameterof the orices constituting the lens being of similar size and adapted to produce a symmetrical electrostatic eld thereabouts;

Fig. 2 is a diagrammatic sectional view' of a similar device wherein the orificed electrodes are 4 of unequal diameter and so arranged that similar device wherein the orlced electrodes are of unequal diameter and so arranged that of an object. not shown, is focused upon this scribed in the Flory and Morton application .tained in a preferably highly evacuated container I. A semi-transparent photosensltive cathode 3, curved to correct for curvature of the image i'leld and forse-called pin cushion distortion is disposed adjacent to the'leading end of the tube I. A preferably inverted optical image curved photosensitive cathode 3 by means of a suitable lens system exemplified in the drawing by the single lens 'I. Such optical lens system may be constructed of optical glass if the device I is to be used for examining visible images, or quartz if ultra-violet light from an object is to be utilized, or of hard rubber or the like if use is to be made of infra-red light.

Disposed adjacent to, or as shown in Fig. 1, forming part of the opposite end of the tube I, is a semi-transparent fluorescent. screen 9 of willernite or other suitable material upon which electrons from cathode 3 eventually impinge to form an externally visible re-inverted image.

If the electron image is to be utilized for television transmission, the iiuorescent screen 9 may be dispensed with and the image may be directly scanned, for example, as shown in Farnsworth U. S. Patent No. 1,773,980, or it may be thrown upon a planar mosaic electrode which is, in turn, scanned by a cathode ray from an electron gun to provide a train of electrical impulses, as depreviously mentioned. l

The other electrode elements in the tube are designated IIa, IIb, IIc, IId, IIe, I3e and I3. They are preferably symmetrically arranged in the order shown about the long axis of symmetry of the container I so that they form a multi-part conduit between the terminal surfaces 3 and 9. Electrodes IIe and I3e are provided with anges Hf and I3f which extend inwardly in spaced face-to-face relation. These flanges IIf and I3f are provided with similar aligned apertures I Ig and I3g. The ring-like members. II are the focusing electrodes'and serve to direct the electrons toward the reduced apertures II g and I3g from whence they are accelerated by the positively charged tubular anode I3 vtowards the Screen 9.

As indicated in the drawing, the metal surfaces IIf and I3f surrounding orifices ligand I3g are electrically and mechanically united, respectively, to the focusing electrode IIe and to the anode or accelerating electrode I3. If desired, however, they may'be separate disc-like members. The exact dimensions of these equal apertures will depend upon the degree of magniiication required, the lower limit in size being determined by the ability to direct theelectrons from the cathode therethrough without impinging against the surrounding metal. Electrons which may be released by impact of stray electrons from the cathode 3 against the inner surface of the focusing electrodes will be arrested by that surface of the inwardly directed member If which is on the side of the cathode.

The anode or accelerating electrode I3 is in the form of an elongated open-ended cylinder formed either of solid conductive material or of a foraminous metallic sheet.

The relative potential distribution among all of the focusing electrodes II is the same regardless of the sharpness of the focus required so that, if desired, individual resistors I2a-I2e may be permanently connected within the tube, for instance in the manner shown in copending application, Serial No. 48,982, to Zworykin, et al., :Bled October 30, 1935. These resistors are of such value as to supply the several electrodes II with separate potentials each of increased magnitude with respect to its 'next preceding electrode.

With the resistors I2 included within the tube,

, but three external leads are required. These leads are connected to a vsuitable source of current exemplified in the drawing by the battery A and by the potential divider AI. The cathode 3 is preferably connected to the negative terminal and the anode I3 and the electrode I3e, integral therewith, to the positive terminal of the direct current source by leads 3' and I3', respectively. Acustable lead II' supplies operating potentials for all of the electrodes II, the necessary dis-` tribution obtaining by reason of the resistors I2 previously described.

Alternating, instead of direct, current may be employed if desired, provided the alternations are at a rate sufficient to ensure'persistence of vision.

Operation of the device of Fig. 1 is characterized by the presence of a substantially symmetrieal family of equipotential surfaces about the reduced orifices II g and I3g. As indicated by the dotted lines IIh and I3h, the contour of these surfaces corresponds to the outline of a bicconvex optical lens having opposite surfaces of the same radii of curvature.

The device of Fig. 2 is similar in all respects to that of Fig. 1 except that the reduced apertures, here designated ZIg and 23g, respectively, are of unequal diameter, the larger orice 2Ig being on the cathode side of the lens. This results in different radii of curvature on opposite sidesl of the lens and a shift in the cquipotential surfaces 2Ih-23h so that the effective electron lens is moved closer tothe cathode with a resultant increase in magnification.

In Fig. 3, the orifice 33g on the anode side of the lens is of a greater diameter than the orifice 3Ig on the cathode side. Here, as indicated by-the dotted line 33h, the shift in the equipotential surfaces is more pronounced on the side of the direction of electron travel so that, the tube being otherwise the same as the tubes of Figs. 1 and 2, the effective electron-lens is moved closer to the creen 9 with a resultant decrease in magnificaion.

The electron-lenses of the devices illustrated by Figs. l, 2 and 3 are each designed to achieve a single ratio of magnification. They may, however, be rendered capable of producing electronimages of various desired degrees of magnification by providing an adjustable lead from one of the small oriiced electrodes and a separate lead to the focusing ring-like electrodes. In this case, the internal resistor I2e connecting the focusing electrodes and the selected magnifying electrode (say IIe, Fig. 1) is dispensed with. Such modification is deemed within the scope of copending application Serial No. 52,289 to George A. Morton, filed November 30, 1935.

While the series of focusing rings (II Fig. l, for example) are shown as separate and connected at different points to the voltage divider I2 it is, of course, apparent that the surfaces II may be made cmtinuous. In this case' the surface II will of itself provide the different voltages due to the voltage gradient between the ends thereof. A surface of this character may be formed as a thin sputtered high resistance conamasar ducting nim upon the inside wall of the glass envelope or even a separate cylinder positioned within the main envelope Awith appropriate conu going is to be interpreted as illustrative and not in a limiting sense except as required by the prior art and by the appended claims.

What is claimed is:

1. In an electro-optical system, a photosensim tive cathode adapted to release a family of electrons in response to the impression of a light image thereon, a screen, a conduit intermediate said cathode and screen through which said elec?.m trons pass to form an electron image on said screen corresponding. to said light image, said conduit comprising a plurality of apertured members, the aperturesA in two adjacent or said members being each oi a diameter less than that oftheothermemhers.

2. The. invention as. set forth in claim 1 wherein the diameters of the apertures in said two adjacent members are substantially the same.

3. The invention as set forth in4 claim 1 wherein the diameter of the aperture in that one of said two adjacent members which is nearer the cathode is greater than the diameter of the aperture in the other of said two adjacent members.

4. The invention as set forth in claim 1 wherein the diameter of the aperture in that one of said two adjacent members which is nearer the screen is greater than the diameter of the 'aperture 1n the other of said two adjacent members.

5. In an electro-optical system, a photosensitive cathode adapted to release a family of electrons in response to the impression oi.' a light image thereon, a screen, a conduit intermediate said cathode and screen through which said electrons pass to form an electron image of xed magniiication on said screen corresponding to said light image, and apertured electrode means interposed in said conduit for rendering the fixed magnification of said system other than that dictated by the physical length of said conduit.

GEORGE A. Mort'roN.A

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