US2365006A - Cathode ray tube and light beam control means - Google Patents

Description

Dec. 12, 1944.

R. E. RICKETTS CATHODE-RAY TUBE AND LIGHT BEAM CONTROL MEANS Filed July 24, 1942 505672 72 2 CZ/6 Z55 Patented Dec. 12, 1944 CATHODE RAY TUBE AND LIGHT BEAM CONTROL MEANS Robert Eugene Rlcketts, Plainfleld; N. J.

Application July 24, 1942, Serial No. 452,221

7 Claims.

source, a source of secondary emission electrons which are produced by the'bombardment of an electron emitting element by the primary or initially produced electrons and which are com densed with the primary electrons into the spot or trace producing ray which is directed against the fluorescent screen and is caused to move thereacross in the customary manner.

Still another object of the invention is to provide an improved cathode-ray tube having. as the cathode for the production of the primary electron streams, a light sensitive electron emitting screen or wall in an end of the tube which is activated by the application thereto of a pencil or beam of light.

Still another object of the invention is to provide an improved cathode-ray tube having the light sensitive electron emitting screen forming the cathode, with a novel means for controlling or varying the intensity of a light beam applied thereto, in accordance with or in response to received signals or signal impulses, whereby to obtain the desired variations in intensity of the electron beam falling upon the fluorescent screen within the tube.

Still another object of the invention is to provide in association with an improve cathoderay tube of the character stated, an improved light beam intensity controlling cell operating upon the principle of the well known Kerr cell, in response to variations in received signals.

The invention will be best understood from a consideration of the following detailed description taken in connection with the accompanying drawing, it being understood. however, that the invention is not to be considered as limited by the specific illustration or description but that such illustration and description constitute a preferred embodiment of the invention.

In the drawing:

Figure 1 is a view illustrating the light beam control means, and a portion of the tube.

Figure l is a diagrammatic longitudinal section of the tube.

Figure 2 is a fragmentary detail showing a modified embodiment of the cathode screen.

Referring now more particularly to the drawing the reference character E generally designates the envelope of the present cathode-ray tube. This envelope may be formed of glass, metal or other suitable material in accordance with practice. This tube may be of any suitable design but is here illustrated as of conventional design in having the relatively long straight portion l0 having the closed end wall H and merging at its other end in the flared or conical portion l2 which is closed by the rounded front or convex wall l3. Upon the inner face of the wall I3 is applied a coating or layer of a suitable fluorescent material 14.

In accordance with one embodiment of the present invention the rear end wall I I of the envelope is covered upon its inner side with a layer or coating l5 of any suitable light sensitive mate rial such as, for example, some alkaline metal like potassium or rubidium which emits electrons when acted upon by light.

Suitably spaced from the electron emitting coating or electrode I5 is the first anode l6 and disposed adjacent this anode but electrically spaced therefrom, at the end of the anode nearest the cathode I5 is the grid screen IT. This grid screen may be placed to encircle the end of the first anode nearest the cathode as illustrated but is, as previously stated, in spaced relation therewith.

The first anode I6 is in the form of a tube or sleeve and encloses a series of diaphragms l8 each of which has an opening l9 therethrough. These openings are aligned in a path oblique to the axial center of the anode for the purpose of condensing the electron stream entering from the cathode, to fiow out of the forward end of the first anode at an angle or oblique to the axial center of the envelope for the purpose hereinafter stated.

Completing the electron gun is the second anode 20 which is located in the customary manner in advance of the first anode and which is of tubular or sleeve like form and has within it the diaphragms 2| each of which has a central opening 22 for the passage of the electron stream. The apertures 22 are aligned upon the axial center of the envelope and of the second anode so that the electron stream when flowing to the fluorescent screen without being acted upon by the deflection elements, will travel along the axial center of the envelope.

interposed between the first and second anodes is an electron multiplier unit which is indicated generally by the numeral 23. This unit 23 is made up of a number, preferably four, of electrically separated plates 25 which are of arcuate cross-section. These plates are assembled, as illustrated, to form a tube which is coaxial with the envelope and with the first and second anodes.

The plates 23 of the electron multiplier unit 23 are of a metal having a low work function which when bombarded or struck by electrons moving at high velocity, will emit electrons. The first electrode is constructed and arranged so that the electron stream passing therethrough will be directed at an angle against the inner surfaces of the plate of the multiplier unit so as to create a secondary electron emission in this unit. If such a unit were in the form of a single tube the electrons impinging against the inner surface thereof and those electrons caused to be emitted .by such impingement would follow a sinusoidal path. By forming such a tubular unit into sections as illustrated and by applying electric potential to the separate sections or plates, the electrons will, instead of describing one revolution, travel through many revolutions within the unit and by impingement a large number of times against the inner surfaces of the plates before leaving the unit, cause the emission of large numbers of secondary electrons which will enter the stream passing on from the multiplier unit to the second anode.

Any suitable means may be employed for applying potentials to the plates 25 of the electron multiplier unit, one means being here shown as in the form of a number of series connected sources of potential 28 each of which is connected by a pair of conductors 21 across two oppositely positioned plates 23.

The inner surface of the envelope is covered by a suitable metallic current conducting coating 28 which extends from a position adjacent to the cathode I! to the opposite end of the envelope where it terminates short of the fluorescent screen II. This coating functions in the customary manner to drain off electrons from the fluorescent screen and is electrically connected with the grid screen ll in the arrangement shown when the grid screen is not employed to control the intensity of the electron stream under the action of the modulated current signals received, when the tube is employed in receiving television signals. When this grid screen is made use of for controlling the intensity of the electron stream, the conducting coating 28 may be connected with the second anode is is customary, the grid screen ll then being hooked up with thesignal receiving circuit to retard or accelerate the electrons emitted from the cathode. in response to signal variations.

The elements of the electron gun are here illustrated as being connected with a conventional voltage divider 23 whereby the desired potentials may be applied to the cathode, grid screen and anodes.

Deflection of the electron beam, designated B, to eifect the desired movement of the spot 23' may be accomplished by the employment of the magnet cells 30 or by the use of the well known deflection plates, not shown.

While there has been illustrated in association with the electron multiplier unit 23, a cathode consisting of a light sensitive material coating at the inner end of the tube, the multiplier unit may be employed, if desired, with a regular or standard hot filament cathode for generating the electron stream or beam.

The invention also contemplates the employever since this formation facilitates the focusing of the emitted electrons toward the center of the grid screen and into the adjacent end of the first anode.

The numeral 3| designates a light source for the production of a light beam 32 directed against the light sensitive electrode I! or 30'. This light beam 32 is preferably, though not necessarily, passed through a condensing lens 33, and then a polarizer 34 such as a Nicol prism, to a second Nicol prism 35 which functions inthe well known manner as an analyzer for the plane-polarized light beam issuing from the first prism.

interposed between the prisms 34 and 33 is a light beam rotating unit which is indicated generally by the numeral 36 and by means of which the intensity of the light beam 32 can be diminished or caused to increase to its maximum before striking the electron producing cathode in the end of the envelope. I

A second lens 31 may, if desired, be interposed between the analyzer prism and the cathode of the tube or envelope.

The light beam rotating unit 33. is of novel design in that it comprises four spaced parallel transversely arcuate plates 33 which are grouped about and parallel the light beam, which beam passes along the center of the space between the grouped plates.

The plates of the light beam rotating unit are coupled as illustrated, through the medium of the transformer unit 33 with the signal receiving sy tem to receive the incoming signals. As a result the electrostatic field between the plates 33 is constantly varied in intensity in accordance with variations in the received signals. to thereby rotate the plane-polarized light beam so that more or less thereof may pass through the analyzer prism 35. The light beam density controlling unit or rotating unit 33 in effect consists of two Kerr In place of the light beam rotating unit 33 or Kerr type cell there may be used in this system, if desired, a supersonic light valve.

In the multiplier unit 23 a number of diilerent metals may be employed for the production of the desired secondary emission of electrons. As an example, there may be employed silver or platinum, silver having a coating of caesium or plati-' mim coated with caesiated silver, caesium having a coating of caesium oxide, barium having a coating of barium oxide, barium oxide on silver and silver plated platinum. In general, caesium coated metallic plastes or bodies will function as desired, using metals having a low work function. Rubidium having a coating of rubidium oxide, or silver on platinum with a rubidium or other alkali metal oxide may also be employed.

Metals having a low work function will produce the desired secondary emission when stretched or placed under tension and such stretching or tensioning may be given to the above stated metals. Parkarized steel with applications of the above stated metallic oxides may also be employed.

It is to be understood that the envelope E of the present invention may be filled or charged with a suitable gas which would aid in the develaccomplished with a lower current consumption and without sacrificing desirable features. With this improved cathode-ray tube a larger electron emission is obtained under low current voltage, with a considerably greater sensitivity, than is possible with tubes not having provision for secondary electron emission.

It will also be apparent that a new and novel arrangement is disclosed for controlling the lumen intensity of the light pencil employed for exciting the light sensitive electron emitting substance upon the rear end of the tube.

Reference has been made to the use of Parkarized" steel as a suitable material to be used in the electron amplifier, either alone or as a support for other electron emitting substances. This steel is prepared, broadly, by treating the metal, by dipping or in any other manner, with acids and then with alkalies which tends to make the surface of the metal somewhat rough and porous. Hence, the surface of such metal may be a good emitting surface under certain conditions.

I claim:

1. A cathode ray-tube including a source of primary electrons, a first anode adjacent said source and a second anode, means for generating secondary electron emission comprising 2. cy' lindrical unit interposed between the first and second anodes and arranged to have the electron beam from the [primary source directed therein to and against the inner wall thereof, said unit consisting of metal having the capacity to emit electrons under electronic bombardment, said cylindrical unit being longitudinally divided to form a number of spaced parallel plates, and means for applying an electrical potential to said plates to set up an electrostatic field therebetween.

2. In a cathode-ray tube, a primary source of electron emission at one end of the tube, a first anode disposed in advance of said source, a grid screen adjacent said anode for directing the electron flow from the source to the center of the first anode, a second anode spaced from the first anode, said first anode being constructed and arranged to focus the electron stream toward the second anode along a path oblique to the axial centers of the anodes, a tubular secondary electron emitting unit disposed coaxially with and between the first and second anodes and spaced therefrom, the focusing anode functioning to direct the electron stream into and against the inner wall of said unit, and means for establishing an electrostatic field within said unit.

3. In a. cathode-ray tube, a primary source of electron emission at one end of the tube, a first anode disposed in advance of said source, a grid screen adjacent said anode for directing the electron fiow from the source to the center of the first anode, a second anode spaced from the first anode, said first anode being constructed and arranged to focus the electron stream toward the second anode along a, path oblique to the axial centers of the anodes, a tubular secondary electron emitting unit disposed coaxialiy with and between the first and second anodes and spaced therefrom, the focusing anode functioning to direct the electron stream into and against the inner wall of said unit, means for establishing an electrostatic field within said unit, said source of primary electrons comprising a screen of light sensitive electron emitting material.

4. A cathode-ray tube structure as set forth in claim 2 in which said source of primary electrons comprises a screen of light sensitive electron emitting material, and means for applying a negative potential to said screen and gradually increasing positive potentials respectively to the grid screen and first and second anodes.

5. A cathode-ray tube structure as set forth in claim 2 in which said tubular unit comprises a series Of longitudinal spaced parallel plates disposed in electrically separated relation, means for applying electric potentials of opposite polarity to opposite plates of said unit, and means for applying a negative potential to said light sensitive screen and progressively positively increasing potentials respectively to the grid screen and first and second anodes.

6. An electro-optical system comprising an evacuated tube having a fluorescent screen at one end, a screen of light sensitive electron emitting material in the opposite end of the tube designed to emit electrons under the action of light falling thereon, spaced first and second anodes within the tube and aligned between said screens, an electron steam deflecting means, said second screen when subjected to a light beam emitting electrons, said anodes being arranged to receive and focus said electrons onto the first screen, alight source disposed in position to project a light beam on the second screen, a pair of Nicol prisms interposed between the light source and the second screen, and means interposed between the Nicol prisms for axially turning the light beam in response to changing electrical signal impulses to control the intensity of the light beam falling upon said second screen.

'7. A system as set forth in claim 6 in which said last means comprises two pairs of electrically separated plates disposed around and parallel with the light beam and means for applying electric potentials of opposite polarity to the opposite plates of each pair.

ROBERT EUGENE RIGHT-TS.

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