US2251332A - Cathode ray device - Google Patents

Description

Aug. 5, 1941. F. GRAY 2,251,332

CATHODE RAY DEVICE Filed Marh 31, 1938 2 Sheets-Sheet l EXTERIOR MGNE T J ro 4m; da SWEEP VLTGE To By 42 45 SWE W27@ VOLTAGE l A T TOR/VE V Aug. 5, 1941. F. GRAY 2,251,332

CATHODE RAY DEVICE Filed March 31, 1938 2 Sheets-Sheet 2 M fC TTOR/VEV n mm @n w l r f 6 5. f m c. W. W G Hun. DLG W ...l SW F MT om. 6 UC n.4 y

VS RN 6 A0 9 J mm w mm n E uw NT P .M 8 wc E 7 EE w n sa m MODUL A TING VOL 7A GE Patented Aug. 5, 1941 oA'rHoDE RAY DEVICE Frank Gray, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 31, 1938, Serial No. 199,192

23 Claims. (Cl. Z50- 27) This invention relates to electro-optical devices and more specically to cathode ray tubes in which secondary electrons are generated and utilized.

A cathode ray tube is known in which a beam pvices of this character.

It is an object of this invention to provide novel and useful forms of cathode ray tubes of the type utilizing a beam of secondary electrons generated by the cathode beam and methy ods of and means for controlling and utilizing such beams of secondary electrons.

VIn accordance with the invention, in one embodiment thereof, shown by Way of example, there is provided a cathode ray device comprising an electron gun for generating a beam of primary electrons, a target in the path of the beam which is made of or has a coating of material which will emit secondary electrons when bombarded with primary electrons from the beam, this target being mounted at an angle with respect to the axis of the electron gun, a pair of deecting plates for causing the beam to pass over the successive elemental areas of an elemental 'line of the target, and a fluorescent screen in a plane parallel to the axis of the primary electron gun and closely adjacent the target, said screen being positively polarized with respect to the target by means of a source of potential which is connected to a metallic coat-` ing on the screen, the Vcoating having an elongated aperture therein. Secondary electrons are attracted by the metallic coating to cause the successive elemental areas of an elemental line of the screen adjacent the aperture in the metallic coating to fluoresce', thus providing a moving source of light for scanning successive elemental areas of a moving picture lm. Due to the fact that the beam is deflected while it is moving 'at low velocity, only relatively small deflecting voltages are required. An intense beam can be attained at the lluorescent screen if the target is formed of or coated with a matemetallic coating which acts as an accelerating electrode. The intensity of the secondary electron beam may be controlled by varying the voltage applied between the cathode of the electron gun and a control cylinder surrounding the cathode.

In a modification of the above embodiment the fluorescent screen is mounted on a glass member located parallel to the secondary emitting target and in such a position that the axis of the light emitted from the iiuorescent screen substantially coincides With the axis of the primary electron gun. The screen member is preferably shielded from the secondary emitting target by a metallic member having an aperture therein through which the secondary electrons pass on their Way to the fluorescent screen. In order to cause the axis of the emitted wedge of light to coincide with the axis of the electron gun, an exterior magnet is used to give a preliminary deflection to the beam of primary electrons.

In another embodiment of this invention, the primary electron beam is modulated by deflecting it in a direction transverse to the scanning direction in order to control the number of secondary electrons which pass through the aperture in the shield surrounding the composite screen consisting of a slitted metallic plate and a glass member having a fluorescent coating thereon.

T'he invention will be more readily understood from .the following description taken in connection with the 'accompanying drawings forming a part thereof in which:

Fig. 1 shows an electro-optical device for scanning a moving picture film for television transmission embodying a cathode ray tube utilizing secondary emission of electrons;

Fig. 2 is a View looking toward the fluorescent screen of the cathode ray tube of Fig. 1;

Fig. 3 shows a modiiication of the device shown in Fig. 1;

Fig. 4 is an enlarged View of a portion of the tube shown in Fig. 3;

Fig. 5 shows another cathode ray tube employing secondary emission in which a different method of modulating the primary electron beam is used;

Fig. 6 is an enlarged View of the target portions of the cathode ray tube shown in Fig. 5; and

Figs. '7 to 9, inclusive, show the relationship between the secondary electron beam and the targetl portions shown in Fig. 6.

Referring more particularly to the drawings,

Fig. 1 shows a cathode ray device III for scanning a moving film II for television transmission. The device I comprises a gas-tight container enclosing an electron gun for producing a moving beam of primary electrons and for focussing and accelerating this beam toward a target I2 which is mounted in the end of the tube II) remote from the electron gun, and means such as a pair of deflecting plates I3, I4 for deflecting the beam along a predetermined linear path of the target I2. In a Wall of the tube there is a layer of uorescent material I5 which is entirely covered, with the exception of a narrow linear gap I6, by a coating I'I of metallic material. If desired, the iiuorescent material I5may fill only the gap I6 and the metallic coating be arranged adjacent the wall of the tube. External to the tube I0 is mounted a suitable lens system, which is represented by way lof example as a single conveX lens IB, for focussing an image of the linear iiuorescent screen I5 upon the moving film II which is caused to 'move in a direction .transverse to the movement of the light beam on the uorescent strip I5 by means of reels I9 and 20 actuated by suitable driving mechanism (not shown). The moving beam of light from the screen I5 passes through the aperture 2I in the mask, 22, after having been modulated by the light-tone values of .the successivelyscanned elemental area-s of the Vobject on the film II, to a photoelectric cell 23 which is connected by terminals 24, 25 to any appropriate television transmission circuit (not shown).

The electron gun arrangement in the tube III comprises a cathode 3U, a first anode 3 I, a second The control element A34 preferably comprises a;

cylindrical. member having an apertured diaphragmY 31 opposite the end of the cathode 3D near the rst anode 3I. The control element 34 is preferably placed at a negative potential with1 respect to the cathode by an adjustable source of direct potential 33.

The first anode 3| comprises a cylindrical member having an aperture'd disc 43-at the end thereof remote from the cathode 3B.

spect to that of the cathode by means of a suitable source of direct potential 3i).

The second anode 32 preferably comprises a The rst anode 3|.. is placed at a potentialwhich is positive with remetallic cylindrical member having two apertured...

diaphragms 4B and 4I therein. The second anode 32 is placed at an appropriate positive potential with respect to the potential of the iirst anode SI by means of a source of direct potential 42.

'Ihe third anode 33 comprises a cylinder having The relative potentials of the 'I'his beam of primary electrons is caused to move back and forth in a line at right angles to .ing lm II.

52 by means of a source 65.

the plane of Fig. 1 by means of a sweep voltage applied between the pair of plates I3 and I4. This sweep voltage, preferably from a saw-toothed wave form generator (not shown), is applied to the plates by means of coupling condensers 46 and 41. A high resistance 48 is connected between the plates, the mid-point 49 of which is connected to the third anode 33. Any suitable saw-toothed generator may be used but it is preferable that it be a generator of a balanced sweep wave. Such a generator and the advantages thereof are disclosed in Patent 2,178,464, issued O-ctober 31, 1939, to M. W. Baldwin, Jr. By applying a balanced sweep voltage to the balanced circuit comprising capacities and 4l' and the resistance 42, the mid-point of which is connected to the anode 33, defocussing of the beam by the sweep voltage is prevented.

A source of potential 5I] is applied between target I2 and the conducting coating I'I in such .a manner thatthecoating I1 is placed at a high positive potential with respect to that of the target I2. This causes the secondary electrons emitted from the target I2 to be accelerated toward the aperture I6 Vcontaining the uorescent .material I5. VThus, ify the primary beam is caused to scan. a `single line 4of the target I2, the secondary "beam scans the linear fluorescent screen ,I 5, thus generating a moving beam of light which is focused by the optical system I8 upon the mov- The lm II is either moved continuously, in which event the screen is scanned on a slight bias to take account of the movement of the lrn or else proper gear movement is provided to cause the film I I to move intermittently between successive scannings of the various elemental lines. The light from the screen I5 is thus modulated by the tone values of the successively scanned elemental areas of the lm II and directed upon photocell 23 or other appropriate pick-up device where it is converted into image signals which may be conducted by means of lines 24 and 25 to an appropriate output circuit which includes biasing means for the photocell anode.

In order to direct the secondary beam to the approximate center of the screen I5, an exterior magnet 5I may be used. This magnet shifts the position of the scanning path of the primary beam onthe angularly arranged target I2 and thus shifts the secondary beam along the axis of the tube.

Referring now to theV modication shown in Figs. 3 and 4, the means for forming and deflecting the electron beam in the tube 6D of Fig. 3 are similar to those in the tube III of Fig. 1. In Figs. 3 and 4, however, the target and screen are 'modied so that the axis of the wedgefof light placed from the axis of the primary electron gun in order that the center line of the fluorescent screen 5I maylie on this axis. The primary beam is deflected upon the target 4I2 by means of the exterior magnet 5I. The metal plate 62 is placed ata high positive potential with respect to the potential of 'the target I2 by means of source65 andthe vshield G3 is placed at a potential somewhere between that of the target I2 and the plate The region surrounding the aperture 64 in the shield 63 thus VServes to define a cylindrical electron lens which A3l and v82.

ythat of the target l2.

an opening 96 for the passage of light from the focuses the secondary electrons'emitted from the target l2 to aV spot onthe fluorescent coating 6l. This spot gives rise to a moving light beamwhch is focused by means of the lens system I8 as in and for the purpose of the arrangement shown in Fig. 1.

In the tube it shown in Fig. the intensity of the secondary beam impinging upon the luorescent screen 'H is modulated in accordance with the deflection imparted to the beam of primary electrons. For this reason the electron beam forming and `deliecting systems are slightly different from those shown in Figs. 1 and 3. Due to the fact that the electron beam is modulated by deflecting the primary electrons, the primary electron gun is simplified by the removal ofl the control element 34 and the rst and second anodes are combined into a single cylindrical lstructure 72 which comprises the rst anode of the gun in Fig. 5. This cylinder 12 has apertured diaphragme i3 and T4 therein and a portion of the cylinder surrounds the cathode 30. The rst anode is placed at a positive potential with respect to the cathode 3G by means of the source of potential l5.

The second anode 'i6 comprises a cylinder having an vapertured diaphragm "H therein. This anode, which is similar to the third anode 33 in Fig, ll, is placed at a positive potential with respect to the iirst anode "i2 by means 'of the source'. rThe relative potentials of the anodes 'i2 and 16, the spacings therebetween, and the sizes of the apertures in the diaphragms are so chosen that the electrons from the cathode Si! are focused to a fine spot on the target l2 which is made of or has a layer of secondary emitting material.

This primary electron beam is deflected in a line which is substantially perpendicular to the plane of Fig. 5 by means of a sweep voltage applied between the pairs of plates I3 and I4 in a manner similar to that described in Fig. 1. The beam of-primary electrons is also deflected from left to right in the plane of Fig. 5 by means of modulating signals applied between the pairy of plates T9 and 89 through coupling condensers A high resistance 83 is connected between the plates, the mid-point-8f of which is connected to the second anode '16. The circuit shown in Fig. 5 is suitable when the modulating signal is balanced with respect to a fixed potential but it is obvious that the arrangement of this invention is equally adaptable to the situation where one of' the plates 18 and'BJ-is connected to a point of iixed potential such as, M

for example, the potential of the second anode T6, and the other plate allowed to swing in po1 tential in accordance with the variations of the modulating voltage.

As the electrons of the primary beam'strike the target secondary electrons are emitted and directed through the slit opening 9i in the metal plate 92 to strike the fluorescent coating 'Il which is mounted on a glass supporting plate 93. The secondary beam is focused by the electric elds at the shield 9d which has an opening for the passage of the secondary electrons and is placed at a potential intermediate that of the target I2 and the metal plate 92 by means of a source of potential 8l. The source'S'l isnot as'large as the source 98 which places the plate 92 at a high positive potential with respect to lThe shield 94 also has fluorescent screen.

kthe plate.92.

Reference will now be made toFigs. 6, 7, 8 andv9 in order to more fully explain the operation of the tube shown `in Fig. 5. Fig. 6 is an enlarged View of the target l2 and the fluorescent coating H when the primary beam is deflected into a position corresponding' to maximum signal strength. Figs. 7, 8 and 9 show the relation'ol the secondary beam to these elements for positions of the primary beam corresponding to less than maximuml signalY strength.

The secondary beam may be modulated in two ways with the set-up shownin Fig. 5. First, consider that the aperture 95 in thescreen is made large enough so that if the secondary beam ismoved anywhere within the range-from X to Y (Fig. 6) the full secondary beam will pass through the-aperture 95. Theaperture 9|, however, in the plate 92 is made so small that when the primary beam is only in one position, that is, the position shown in Fig. 6, substantially all of the electrons in the secondary beam pass through the aperture 9i. f it is moved above or below the point A shown in Fig. 6 as, for example, to theV point B shown-in Fig. 7 or the point Cin Fig. 8, only 'a small portion of the secondary beam passes through the opening 9| and the light on the fluorescent screen is correspondingly-redueed. `This method of operation is` based onthe ydiscovery that the paths ofthe secondary electrons are independent of theangle of incidenceof the primary beam, and that they are determined by the point at vwhich the secondary electrons are'generated on -the target and by the electric fields existing between-the target and electrode S, and'between the electrodes 8dand 92. Considering that-thevprimary beam is moved from the'point X to thepoint Y through all intermediatepoints, the beam ofsecondary electronsmoves successively'from aposition where all ofthe 'electrons are impinging upon the lower portion of the plate vr91, through a position` (-Fig. 8) vwhere some ofthe secondary electrons-pass through the opening 9i and part impinge upon the 4lower Vportion of plate 92, through a position where substantially all of them pass through the aperture 9i to the `fluorescent coating H (Fig. 6), through a position where a part impinge upon the upper portion of the `plate 92-and `a. part pass through `the opening -SI (Fig. '7), and iinallyito the position where al1 of them impinge upon the upper-portion of It-will be apparentthatthe modulating curve is-substantially a probability curve and either half of this curve may be used in practice, proper biasing supplied by any suitable means such as, for example, a battery connection between theplatesl and 96. Such an arrangement is shown in Patent 2,168,760, issued August 8, 1939, to C. J. Calbick. With the proper bias, all of the motion of the beam is fromthe ,point representing no impingement of the secondary beam upony fluorescent screen V7i, which -point may be tothe left or right of the center point vas desired, depending upon the polarity of the biasing means applied between the plates .19 and, to the central point representing full impingement of the secondary beam upon the screen 1|.

Inthe second arrangement-for modulating the secondary electron beam (see Fig. 9), the aperture in the screen 9d is made `small andthe aperture 9i in the plate 92 is made relatively large. In this'arrangement all of'the secondary electrons which-get through the aperture 95 will .also get through the aperturel but the primary beam must be in such a position, corresponding to the central point A shown in Fig. 9 for the entire secondary beam to pass through the opening 95. In the position D shown in Fig. 9 only a portion of the secondary beam passes through the aperture 95, the remaining portion of the secondary beam impinging upon the lower part of the shield 94. Movement of the primary beam above and below the point D will vary the number of electrons passing through the aperture 85 and hence the intensity of the spot on the uorescent screen 1|.

With either method of modulation, the light emitted by the fluorescent coating 'H is dependent upon the number of secondary electrons which reach the coating l l This light is focussed by a lens system represented by the single lens 99 to make a track record on a moving lm or, if desired, it may be used to project an image on a screen when the light beam is also moved in a transverse direction from that caused by the sweep voltage applied between the plates I3 and I4 by any suitable means, such as by mirrors. It will be apparent from the description above that the modulating voltage applied between the plates 19 and 8D has substantially no effect on the movement of the moving light beam emitted from the fluorescent coating 7|; this voltage serves merely to modulate the intensity of the light beam.

It will be apparent that other modifications may be made in the invention as above disclosed, the scope of which is indicated by the appended claims.

What is claimed is:

1. A cathode ray device comprising means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, means for causing said beam to scan said target along a substantially linear path, and an accelerating electrode for said secondary electrons in close proximity to said target, said electrode having a linear opening therein parallel to said linear path through which opening the secondary electrons pass.

2. A cathode ray device comprising means lor generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, means for causing said beam to scan said target along a substantially linear path, an accelerating electrode for said secondary electrons in close proximity to said target, said electrode having a linear opening therein parallel to said linear path through which opening the secondary electrons pass, and a coating of iiuorescent material adjacent said linear opening.

3. A cathode ray device comprising means for generating a beam of primary electrons, a target Yfor said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, the center of said target being displaced from the aXis of said primary beam generating means, means for deflecting said beam so that it impinges upon said target, means for causing said beam to scan said target along a linear path, and a metal plate parallel to said target, said plate having a coating of uorescent material thereon.

4. A cathode ray device comprising means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, the center of said target being displaced from the axis of said primary beam generating means, means for deecting said beam so that it impinges upon said target, means for causing said beam to scan said target along a linear path, and a metal plate located parallel to said target in such a position that its center is located substantially on the axis of said primary beam generating means for receiving said secondary electrons.

5. A cathode ray device comprising means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, the center of said target being displaced from the axis of said primary beam generating means, means for deecting said beam so that it impinges upon said target, means for causing said beam to scan said target along a linear path, a metal plate parallel to said target, and a metallic screen having an aperture therein for the passage of secondary electrons from the target to the metal plate, said screen having at least a portion thereof between said target and said metal plate.

6. In a cathode ray device, means for generating a beam of primary electrons, a target capable of emitting secondary electrons upon being impacted by said beam of primary electrons, a plate having an aperture therein adjacent said target, said aperture being of such size that substantially all of said secondary electrons pass through it when the primary beam is in a certain position but small enough so that the number of electrons passing through said aperture decreases as the primary beam is moved to one side or the other of this certain position, and a fluorescent screen adjacent said aperture for receiving the secondary electrons which pass through said aperture.

7. In a cathode ray device, means for generating a beam of primary electrons, a target capable of emitting secondary electrons upon being impacted by said beam of primary electrons, a metal plate having an aperture therein adjacent sairl target, said aperture being of such size that substantially all of said secondary electrons pass through it when the primary beam is in a certain position but small enough so that the number of electrons passing through said aperture decreases as the primary beam is moved to one side or the other of this certain position, a screen member between said metal plate and said target, said screen having an aperture therein large enough to allow the entire beam of secondary electrons to pass therethrough for all positions of the primary beam within a predetermined range of movement.

8. In a cathode ray device, means for generating a beam of primary electrons, a target capable of emitting secondary electrons upon being impacted by said beam of primary electrons, a diaphragm having an aperture therein adjacent said target, said aperture being of such size that substantially all of said secondary electrons pass through it when the primary beam is in a certain position but small enough so that the number of electrons passing through said aperture decreases as the primary beam is moved to one side or the other of this certain position, a screen member between said metal plate and said target, and means for placing said target, plate and screen at such relative potentials that the secondary electrons from said target are focussed into a beam.

9. The method of varying the intensity of a beam vof light infa cathode raydevice having means for vgenerating.v a primary` beam of electrons, a target which emits" secondary electrons When the primary beam impinges thereon, and a member vupon Which said secondary beam impinges Which'comprises the step of moving said secondary beam with respect to an aperture adjacent said member to vary the number of secondary electrons passing through said aperture in accordance with the deflection of said primary beam in accordance With signals.

10. In a cathode ray device, means for generating a beam of primary electrons, a target capable of emitting secondary electrons upon being impacted by said beam of primary electrons, a diaphragm having an aperture therein, and means acting upon said primary beam of electrons for varying the position of said beam of secondary electrons With respect to said aperture.

1l. A cathode ray device comprising means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, means for forming the secondary electrons into a beam, a screen, an apertured diaphragm adjacent said screen and means for varying the number of secondary electrons which reach said screen by varying the position of said secondary beam with respect to the aperture in said diaphragm in accordance With the deection of said primary beam in response to signals.

12. A cathode ray device comprising an evacuated container enclosing means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, means for causing said beam to scan said target along a substantially linear path, a conducting coating on a flattened portion of said container which portion is adjacent said target, said conducting coating having a linear opening therein parallel to the scanned linear path on said target, and a coating of fluorescent material adjacent said linear opening.

13. The combination of elements as in claim l2 Y characterized in that the target is mounted at an angle with the axis of the means for generating the beam of primary electrons, and the flat portion of the container is in a plane which is substantially parallel to a plane which contains said axis.

14. A cathode ray device comprising means for generating a beam of primary electrons, a target for said beam capable of emitting secondary electrons upon being impacted by said beam of primary electrons, said target being mounted at an angle With respect to the axis oi the means for generating the beam of primary electrons, means for causing said beam to scan said target along a substantially linear path, a metallic electrode adjacent said target which has a linear opening therein substantially parallel to said linear path, said electrode being mounted in a plane Which is substantially parallel to a plane containing the axis of said means for generating the beam of primary electrons, and a coating of uorescent material adjacent said linear opening.

15. In a cathode ray device, a stationary metallic member having a longitudinal aperture therein, and a source which produces a stream of felectrons which stream effectively moves in a direction transverse to an axial line drawn through the longitudinal aperture at right angles to the plane of the metallic member, whereby the numm ber of electrons passing through said aperture is varied in accordance With the movement of said source of electrons.

16.` The combination of elements as in claim 15 characterized in that the source is a source of secondary electrons.

17. The combination of elements as in claim 15 characterized in that the source comprises a target member for a beam of primary electrons which member emits secondary electrons.

13. The combination of elements as in claim 15 characterized in that the source comprises a target member which emits secondary electrons when impacted by a beam of primary electrons, said target being set at an angle to said axial line.

19. In a cathode ray device, means for generating a beam of primary electrons, a target for said beam, means for causing a relatively large deection in one direction along said target, means for causing a relatively small deflection of said beam along said target in a transverse direction in accordance with signals, an electrode member adjacent said target member, said electrode member having a longitudinal aperture therein in such position that the number of secondary electrons emitted by said target which pass through said aperture is varied in accordance with the transverse movement of said beam of primaryY electrons in accordance With said signals.

20. In combination, a balile member having an aperture therein, a moving source of secondary electrons, and means for directing said electrons toward an aperture in said baffle in such a manner that the number of electrons which pass through the baille will depend upon the position of the source of electrons.

21. In a cathode ray device, means for generating a beam of primary electrons, a target capable of emitting secondary electrons upon being impacted by said beam of primary electrons, and a plate having an aperture therein adjacent said target, said aperture being of such size that substantially all of said secondary electrons pass through it when the primary beam is in a certain position but small enough so that the number of electrons passing through said aperture decreases as the primary beam is moved to one side or the other of this certain position.

22. The method of producing a modulated current which comprises generating a beam of primary electrons, utilizing said beam to generate a beam of secondary electro-ns, directing said secondary beam repeatedly and continuously along a generally linear path, acting upon said primary beam of electrons to slightly vary the position of said beam of secondary electrons in a direction transverse to the longitudinal axis of said path, and continuously selecting and utilizing a portion of said secondary beam in accordance With said transverse Variations thereof.

23. In a cathode ray device, means for generating a primary beam of electrons, a target for said beam having an extended surface upon Which said beam impinges and which emits secondary electrons as the result of the impingement thereon of said beam, means for changing the direction of said primary beam of electrons by different amounts to cause the position of its region of impingement on said target to change, means for directing said secondary electrons away from said target in the form of a beam the axis of which for every position of the primary beam extends in the same general direction as for the other positions whereby said beam of secondary electrons is shifted laterally as the direction of said primary beam is changed, a baille structure spaced from said target in the genera-1 direction of travel of said secondary beam and having a boundary part in position to permit a portion at least of said beam of secondary electrons to pass by said part for one position of the region of impingement of said primary beam on said target and a portion at least of said beam of secondary electrons to be intercepted by said bale structure for a different position of said region, and means for receiving the electrons from said beam of sec- 5 ondary electrons which pass said baiiie structure.

FRANK GRAY.

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