US 3567985 A
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United States Patent Inventor David M. Goodman 3843 Debra Court, Seaford, N.Y. 11783 App]. No. 562,031 Filed June 2, 1966 Patented Mar. 2, 1971 Continuation of application Ser. No. 212,612, July 26, 1962.
X-RAY AND ULTRAVIOLET DETECTORS FOR BEAM-INDEX AND HEATERLESS CATHODE RAY TUBES SINGLE INDEX Primary Examiner-Robert Sega] ABSTRACT: Beam-index and heaterless cathode ray tubes are depicted in combination with elongated and coiled light pipe-scintillators. Penetrating radiation which impinges upon the sidewalls of the elongated light pipe creates scintillations in the interior region thereof. These scintillations are in the optical frequency range and are accumulated in strength as they travel through the light pipe. They emerge at exit terminals of the light pipe in concentrated form. Target screens in the CRT are described which provide the penetrating radiation The concentrated optical scintillations are used for beam-indexing purposes; and are used to excite a nonthermionic cathode. Both the beam-index and heaterless cathode features are applied to cathode ray tubes with multicolor producing target screens.
PATENTED "AR 2 I97\ SHEET 2 or 2 FIG. 9
RED GR BLUE FIEJZ ?g D INVENTOR. l92\NJ|\9/O\ 1, 1 V D M. GOODMAN i I85 BY 1 llllllllllllllllllllll l X-RAY AND ULTRAVIOLET DETECTORS FOR BEAM- INDEX AND HEATERLESS CATHODE RAY TUBES This application is a continuation of my copending application Ser. No. 212,612 filed Jul. 26, 1962.
This invention relates to heaterless cathode ray tubes. It also relates to tubes with target screens that generate position locating index signals when impinged upon by cathode rays and means for detecting the thus generated index signals. In particular, it relates to the detection of index signals in color cathode ray tubes of the beam-index variety.
In my U.S. Pat. No. 3,081,414 granted Mar. 12,1963, I describe a cathode ray tube which-does not require a heated cathode. Instead, the use is made of X-rays which are emitted when the target screen of that tube'is struck by high energy electrons. These X-rays are detected by scintillators to produce light signals which are transmitted through light pipes to where they impinge upon photon-sensitive surfaces which in turn emit electrons. These electrons then are multiplied, controlled, and focused to provide a beam of cathode rays. This beam is scanned across the target screen which causes additional X-rays to be generated, thereby to sustain the operation of the circuit. In such an arrangement the cathode ray beam will increase in magnitude until a saturation level is reached. The resultant energization at a given point of the target screen is proportional to this saturation level and is proportional to the duration of excitation. It is possible then to modulate the output of this heaterless tube by varying the saturation level or the duration of excitation. Thus, this arrangement provides a cathode ray tube with a close loop feedback system which is capable of generating a beam of electrons without requiring the conventional heater-cathode combination.
It becomes desirable in an arrangement such as just described to increase the efficiency of detection of the X-rays. And this is one object of this invention.
Another object of this invention is to provide X-ray detection means of improved sensitivity that may be employed with all types of cathode ray tubes, heaterless or not, having X-ray beam indexing structures.
Still another object of this invention is to provide detection mean, responsive to a penetrating radiation, which may be used to increase the sensitivity of beam-index circuitry employed with multicolor cathode ray tubes.
Various other objects and advantages will appear from the following description taken in conjunction with the drawing. The novel features thereof will be particularly pointed out hereinafter in connection with the appended claims. In the drawing:
FIG. 1 represents a cathode ray tube with a scintillator attached to elements of the electron gun of the tube.
FIG. 2 represents a cathode ray tube with a scintillator having a large area of pickup.
FIG. 3 represents a cathode ray tube with externally disposed X-ray detectors.
FIGS. 1, 2 and 3 represent prior art; they do not form a part of this invention. They are included in the drawing to better illustrate the improvement gained by the instant invention. These three FIGS. are included in the aforesaid U.S. Pat. No. 3,081,414.
FIG. 4 represents a cathode ray tube with a scintillator which is striplike in form. The scintillator shown is positioned adjacent to the outside surface of the tube envelope.
FIG. 5 represents a cathode ray tube with three separate scintillators which are shown adjacent the inside surface of the tube envelope.
FIG. 6 is a cross-sectional view of the tube in FIG. 5.
Fl 7 represents a heaterless cathode ray tube where a single scintillator is wrapped around the envelope of the tube.
F l6. 8 represents a heaterless cathode ray tube where two scintillators are provided similar to the construction of FIG. 7 but which are placed adjacent the inside surface of the tube envelope.
FIG. 9 represents a target screen with three different color producing regions. Associated therewith are three difierent index signals, one for each color producing region.
FIG. 10a illustrates two different levels of excitation of the red strip of the target screen of FIG. 9.
FIG. 10b illustrates two different periods of excitations of the red strip of the target screen of FIG. 9.
FIG. 11 represents a composite target screen that may be used with a cathode ray tube to provide index signals.
FIG. 11a represents an end view of the target screen of FIG. 11.
FIG. 12 represents various terminations of and a transition for the striplike scintillators.
Referring now to the drawing in detail, FIGS. 1, 2, and 3, which represent the prior art as previously noted, are similar in that a cathode ray tube has an envelope 10 containing an electron gun 12 which is used to provide an electron beam. Element 14 is common to the three FIGS. in that it picks up electromagnetic radiation generated at the target screen of the tube in response to excitation by the electron beam. In FIG. 1, element 14 is advantageously positioned in that it is located with respect to the target screen so that it picks up substantially equal amounts of radiation from all parts of the screen. In FIG. 2 element 14 advantageously is provided with a large surface for pickup of the radiation and has a channel provided in its body so that the electron beam may pass from the gun 12 to the target screen. In FIG. 3, elements 14 are positioned outside of the the cathode and near the plane of the front face of the cathode ray tube.
FIGS. 14 represent cathode ray tubes that may be used for color television receivers.
In FIG. 4, the cathode ray tube has an envelope 20 and a target screen 22 positioned on, or near, the front inside surface of the envelope 20. Electromagnetic radiation is shown emanating from the target screen via paths 36, 34, 32, and 30. In one embodiment of this invention, the target screen 22 is constructed so that this radiation is in the X-ray region of the spectrum. A scintillator 26 associated with rod 24 will be excited by those X-rays which travel along path 36 thereby producing flashes of light. These flashes will be conveyed through rod 24 by a series of internal reflections to an exit termination thereof. It can be seen from the drawing that the area of pickup of the X-rays is governed by the frontal area of scintillator 26 associated with rod 24. To increase the area of pickup, and hence the sensitivity of X-ray detection, there is provided in accordance with this invention an elongated scintillating member 28 positioned on the outside of the envelope 20. For this mode of operation it is to be understood that a borosilicate glass is to be used for the tube envelope, and that high anode voltages are contemplated. Alternatively, ceramic materials such as BeD may be used for the funnel section of the CRT envelope. With this arrangement, X-rays emitted by the screen 22 will strike scintillator 28 along its length. Paths 34, 32, and 30 are shown in FIG. 4 to illustrate this point and to provide a visual comparison with the effect produced by the X-rays travelling along path 36. In effect, the sensitivity of pickup now is governed by the length of the member 28, (and by the volume) providing a very distinct advantage.
The rod 24 preferably is made of glass since it is placed in the high vacuum region of the cathode ray tube; furthermore the glass rod itself may be the scintillator as can be seen by referring to U.S. Pat. No. 3,032,659 issued to J. F. Bacon, et al., on May 1, 1962. On the other hand, the striplike member 28 may be made of a plastic scintillator since it is placed on the outside of the tube. Plastic scintillators are commercially available which are easy to machine or form; which are sensitive to X-rays; which will respond rapidly to X-ray excitation; and which will provide light flashes which will decay very rapidly after cessation of excitation. One example of such a plastic scintillator is that made by Nuclear Enterprises, Limited, in Winnipeg, Canada under the identification NE 102. For either type of scintillator, the X-rays generated at the target screen 22 will produce the desired result in that they penetrate into the interior of the scintillator where they produce light, and then by the process of internal reflection much of the light thus generated is transmitted through the scintillator to an exit termination.
It should be noted that if the radiation to be detected is in the optical frequency range such as in the ultraviolet region then the same general conditions prevail. For example, if a conventional 1 -16 (or calcium magnesium silicate: cerium activated) phosphor is used for indexing it will generate ultraviolet radiation (centered at approx. 3800 Angstroms) when excited by electrons. This 3800A. will be transmitted through most CRT glasses (the coating of carbon or aluminum being removed) and will also create scintillations in the plastic phosphor strip 28. But, if the radiation is not to be detected, but is to be collected and transmitted without change in wavelength, then the advantage gained by penetration and scintillation is no longer available. It is a property of light pipes, or optical fiber, that when radiation of the type it can transmit enters the pipe from a side wall the refraction is such that the radiation emerges from the pipe at the other side. In order for this radiation to be piped it must enter the pipe through entrance terminals, the design requirements for which are well-known. The result of such design applied to this case is that the strip 28 can be notched, or serrated, along its length to permit the radiation to enter.
In FIG. 5, a cathode ray tube is illustrated with three striplike scintillators 42, 44, and 46 which are symmetrically positioned inside the envelope of the tube. Although not limited thereto, this arrangement is particularly useful for multicolor cathode ray tubes of the beam-index variety. The three scintillators may respond to the same excitation to increase the sensitivity of pickup by a factor of three. Alternatively, each scintillator may be used to pick up a different radiation, in which case strips 52, 54, and 56 are used to provide suitable filtering. When the three strips are positioned outside the tube the transmissive qualities of the envelope 40 may also be used to provide filtering. Further elaboration is not considered necessary at this time since the art of filtering X-rays and other radiations is well developed. It is of interest, however, to notice from FIG. 4 that a burst of radiation from screen 22 traverses different paths in striking the scintillating member 28; and after scintillation, the light pulses travel through different lengths in the light pipe. The result is that the pulse of light created in scintillator 28 will exist for a greater period of time than that of the exciting radiation. In other words, an instantaneous emission of X-rays at screen 22 results in a pulse of light emerging from the exit end of member 28 which exits for a finite time. It also means that the emergent pulse of light is delayed in time. This broadening and delay of the pulse is a function of the length of the member 28, and of the material of which it is constructed. To delay the output pulse of light further, as may be desired in certain applications, a light pipe member 42' may be provided as illustrated in FIG. 5. This additional delay is useful in synchronizing the operation of color cathode ray tubes where radiation from the target is used to provide high speed index signals. High speed, minimum delay circuits generally are required with beam-index tubes intended to provide high resolution multicolor displays.
As an example, consider the index signal being used to provide synchronization of a three color display using presently known vertical strip target screens. For a 20 inch target screen having 250 sets of color triplets there are 750 strips approximately 25 mils. in width. The horizontal scanning time, less flybaclr, is 53.5[LS8CS. Then, for a linear scanning beam, with a spot size much less than 25 mils, the time spent on each strip is approximately 0.07p.secs., or 70 nanoseconds. For a 5 mil. beam and a 1 mil. index wire an X-ray pulse is furnished of approximately l7 nanoseconds, a fairly crisp index signal. Plastic scintillator 2% will broaden this index signal; by decay time and by travel time. Typically, the decay time is 4 nanoseconds and is self-explanatory. The travel time effect is explained by assuming path lengths 30 and 34 are equal. The radiation via path 34 excites the scintillator, whereupon the light pulse travels to the exit termination near the neck section of the tube. The radiation via path 30 also excites the scintillator, and at the same time, but the light pulse in this case has to travel an additional distance, 33, in the scintillator which takes approximately 2 nanoseconds for a 1 foot length. Thus, the resultant index signal will be lengthened from 17 to 23 nanoseconds, which is still a crisp index pulse. To delay this pulse, member 42' can provide in a 5 foot length approximately l0 nanoseconds of delay which is sufficient to affect vernier control of the overall delay in the index loop. As a matter of comparison, an equal length of coaxial cable with a 509 characteristic impedance, which is frequently used for electrical delay lines, has a delay of approximately 8 nanoseconds. Therefore, the elongated scintillators can greatly increase the sensitivity of detection of the index signal, and furnishes an optical signal which may be adjustably delayed in transit.
There is shown in FIG. 6 a sectional view of the tube of FIG. 5 to show the scintillators more clearly. The scintillators 42, 44, and 46 are shown with filters 52, 54, and 56. These elements are ribbonlike in shape and, as stated, positioned inside the tube. As an alternative to elements 42, 44, and 46 plastic scintillator 49 is positioned on the outside of the tube with a target element 47; and plastic scintillator 51 is shown with a metal jacket 53 for filtering purposes.
With proper design it will be found that the envelope 40 attenuates only slightly the X-rays which are to be detected by these externally positioned scintillators. In contrast thereto, most glasses absorb ultraviolet of wavelength less than 3500A. and if such signals are to be detected (or if low energy X-rays are to be detected) then the internal disposition of the strips is preferred. As a practical matter, the choice of tube envelope and the placement of the detector can best be made after the requirements for the CRT are defined. This is to because there are dozens of detectors and a multitude of indexing phosphors that are available; and an almost endless variation in the compositions of glass and ceramics that can be used for CRT envelopes.
In FIG. 7, a heaterless cathode ray tube is illustrated with a scintillating light pipe element wrapped around the envelope of the evacuated tube. This is done to increase still further the quantity of X-rays which are picked up, as should now be clear. The tube operates as follows: at region 11M) a particle is ionized, as by some natural cause. The negative ion thus formed, perhaps an electron, is accelerated by a high positive voltage to strike the target screen at point 102. X-rays are produced upon impact and radiate in all directions, typical paths being shown at 104, 106, and 108;. Many of these X-rays will create scintillations in member lltl-which results in light flashes travelling in both directions as illustrated at 107. The light pipe properties of the scintillator enables these flashes to be transmitted via routes 112 and 114 to eventually impinge upon a suitable photon-sensitive surface 116. Electrons are emitted from 116 and are amplified by secondary emission at dynodes 118 and 120 (voltage connections to the dynodes and to the target screen are not shown) and are focused at element 124, which thus provides a stream of electrons which are to be scanned by means symbolized by element 126. Element 124 may be a secondary emission dynode equivalent to elements 118 and 120. Element 124 may be a transmission type secondary emission dynode. In effect, the latter stages of the secondary emission amplifier and the element 124 comprise an electron lens so that the beam of electrons normally provided by the heated cathode in a conventional electron gun is in this case provided by the element 124. Additional details of construction on the electron-gun-optics are considered conventional, and therefore are omitted. Emanating therefrom is the stream of electrons 128 which is accelerated to strike the target screen at 1311. Upon impact, additional light are generated. This process is repeated until a steady state condition is reached; then there is a constant beam current provided at 128. The explanation of the manner in which this electron beam may be modulated will be deferred until the explanation of FIGS. focused, 10a, and 10b, but at this point it is clear that the requirement for the conventional cathode heater has been dispensed with.
In FIG. 8, another embodiment of a heaterless cathode ray tube is shown. This tube generates two index signals and may be used in a dual index color receiver. This tube, provides, in effect, two electron beams which can be modulated. Two spiral shaped scintillators 142 and 144 are intertwined, and positioned adjacent the funnel section of the tube. By means of the scintillating process, these detectors provide two optical signals, one travelling through light pipe 146 and the other through 148, to impinge upon two photon-sensitive surfaces 150 and 152. Electrons generated thereby are controlled by grids 154 and 156, and are subsequently amplified and partially focused by dynodes 158 an 160. Then they are further focused, as at transmission dynode 162, to provide an electron beam 164. Deflection coil 140 provides the scanning action of beam 164. The deflection fields created by coil 140 are separated or shielded from the dynodes 158 and 160 and the focusing means 162 so as not to interact. The drawing is exaggerated to more easily identify the various elements and is not to scale. The shielding, and other design features, of secondary emission multipliers are well known and not described further since they do not assist in the understanding of this invention. It should be noted, however, that the high sensitivity of the scintillators provides strong light signals which soon run the secondary emission amplifier section into saturation. Also to be noted is that in this mode of operation if crisp index signals are not required the coils 142 and 144 can be of some length. The operation of this tube is similar to the tube of FIG. 7 except that to different radiations are produced at the target screen. More specifically, there is a first region of the target screen which produces X-rays in a given portion of the spectrum to excite the scintillator 142, and there is a second region which produces X-rays in a different portion of the spectrum to excite the scintillator 144. The beam current that strikes the target screen in the first region produces X-rays, which excites scintillator 142, which causes ejection of electrons from surface 150, etc. The beam current that strikes the target screen in the second region produces different X-rays which excite scintillator 144, which causes ejection of electrons from surface 152, etc. Then, as the beam deflected from region to region of the target screen the source of the electron beam switches back and forth between the channels represented by dynodes 154 and 156 thus making it possible to modulate separately the beam currents. This construction would be used to advantage in self-decoding color television receivers. Since the circuits, per se, form no part of this invention, they are not included.
Referring now to FIG. 9 to discuss methods of modulation of the beam of the heaterless CRT there is shown a target screen comprised of phosphor strips capable of emitting red, green, and blue light in response to electron excitation. X-ray producing particles may be admixed with the phosphors or deposited in layers on either side thereof. Alternatively, the chemical elements of the phosphors themselves may be used to generate the X-rays. As an illustration, the red phosphor of FIG. 9 with its associated X-ray producing particles, will be considered to constitute the entire target screen of FIG. 7. In this case the electron beam 128 will build up to produce a constant intensity red spot on the face of the tube. This is best explained by referring to FIGS. 9 and 10a taken together. Before proceeding with the description, it is to be noted that each strip of a different color requires its own distinct channel for scintillation detection and for controlled amplification of the electron stream. Thus, a two color tube requires a dual index system, as in FIG. 8. A three color system operating in this mode requires a triple index configuration. As long as the scanning field deflects the electron beam .to region 171 to the left of the red strip of FIG. 9 there will be a very small beam current for there are not suitable X-rays generated in this area to sustain the operation of the circuit. Once the electron beam enters the red strip, however, there are X-rays generated, in FIG. 10a there is color (red) produced, and as illustrated in FIG. 10a the beam current builds up. Curves and 172 depict two different levels which the beam can reach. These levels can be governed by controlling the space charges between the dynodes. Typically, a cloud of electrons are allowed to build up in one of the dynode spaces. Then the cloud is released by grid control as is done in other types of electron discharge devices. Alternatively, gain control can be employed in accordance with the teachings of US. Pat. No. 3,036,234 issued to G. D. Dacey on May 22, 1962 to set the saturation level. This patentee describes how semiconductor detectors may be used in place of the secondary emission dynodes to achieve the same end result, namely, a photon generated electron beam.
Referring now to FIG. 10b, there is shown curve 174 which represents a saturated beam current which is gated on for a given period of time. A second curve 176 is shown which represents the same saturated level of beam current but which has a duration larger than that of curve 174. As with the control of the saturation level of FIG. 10a,-so the time duration of FIG. 10b can be controlled by applying suitable potentials (time varying) to the dynodes 1 18 and 120 of FIG. 7. For conventional electron guns the results illustrated in FIG. 10a and 101) can be achieved by the use of an aperture and a deflection field in the vicinity of element 124 of- FIG. 7; and if further particulars are desired I refer to US. Pat. No. 3,038,101 issued to K. Schlesinger on Jun. 5, 1962.
In FIG. 11 a composite target screen is shown which may be used in conjunction with a'receiver system employing two different index signals. FIG. 11a is an end view of the composite screen. Phosphor strips 180, 182, 184, are arranged to be scanned by an electron beam. Aluminum layer is applied over the phosphor strips. Strips 186 and 188 are deposited on the aluminum layer to produce two different index signals. For example, when the electron beam strikes 186, X-rays are produced which are at a given wavelength. And when the beam strikes 188, X-rays are produced which are distinguishable from those produced at 186. STrip 186 may be made of copper particles; strip 188 may be made of nickel. With this construction, the aluminum layer 185 not only provides the conventional function of increasing brightness but it also may serve as a barrier preventing chemical reactions between the index generating strips 186 and 188 and the light producing strips 180, 182, and 184. A second aluminum layer, 190, is deposited over the index strips to prevent the appearance of an ion spot. Since it need not cover the entire screen this layer is shown terminating in the region 192. In certain modes of deflection, and with certain electron guns, this layer may be omitted. However, when used this layer absorbs the negative ions that are attracted to the target screen. It is chosen of sufficient depth to be opaque to the ions but transparent to the electrons and to the X-rays. This construction reduces the masking effect on the index signals that might otherwise be created by the impact of the negative ions on the X-ray emitting strips 186 and 188. Alternative construction is indicated by Xray emitting strips 194 and 198 which are jacketed or surrounded by layers 196 and 199.
In FIG. 12 members 200, 204, and 206 represent terminations that may be used with the scintillating strips. Member 200 has a terminal with layer 202 deposited thereupon. This layer, if made of aluminum for example, is impinged upon by the light pulses traveling through the scintillator, and is reflected to augment the light emerging from the other end of the scintillator. This layer, if jade of an opaque material such as carbon, will absorb the light pulses travelling away from the exit end. This latter arrangement may be desirable when the broadening of the light pulses at the output is to be kept at a minimum. Member 204 has an outwardly flared end which may be used at either end of a light pipe, serving to aid the exit of the transmitted light. It may be used with the coil of FIG. 7 where both ends of he coil are used as exit terminations. The end of member 206 is pinched and may be used to reflect the light from that end. Member 208 is a transition which will convey the light from a circular light pipe to a striplike light pipe,
and vice versa. Clearly, these terminations may be used with the strips of FIGS. 4, 5, 6, and 8 to obtain the properties desired.
It is believed that the foregoing part of the specification has shown how the primary objects of this invention have been achieved. X-rays, or other penetrating radiations such as ultraviolet radiation, generated by a scanning beam of electrons in a cathode ray tube are detected by providing adjacent to and coextensive with the envelope of said tube a special material which is penetrated by the radiation, which scintillates internally, and which transmits the light generated by scintillation through the material by the process of internal reflection. It has been shown how this feature substantially increases the amount of radiation detected in comparison to end-on positioning of the detector as disclosed in the prior art. it has shown that this arrangement will provide a greatly enhanced index signal which is sharp and crisp and which can be used for synchronizing the generation of a multicolor display. It has also been shown how such a detector can be used in conjunction with light sensitive means, and the secondary emission process, to provide the electron beam of a cathode ray tube, either monochrome or multicolor.
l. A heaterless electron discharge device comprising a photon-sensitive source of electron; a target screen adapted to be impinged upon by electrons derived from said source of electrons, thereby to generate electromagnetic radiation; and light pipe-scintillator means disposed in the path of said radiation; wherein scintillations, generated when said radiation excites said light pipe-scintillator, are transmitted via the light pipe to fall upon said photon-sensitive source of electrons.
2. A heaterless cathode ray tube in accordance with claim 1 having an evacuated envelope with a neck section for housing the photon-sensitive electron source, a target screen section, and an intermediate section which connects the neck section to the target screen section; said light pipe-scintillator means being positioned with respect to said neck section so that scintillations generated in the interior region of the light pipe-scintillator are transmitted, via a series of internal reflections, to impinge upon said photon-sensitive source of electrons.
3. A regenerative detector comprising: first means that yield electrons upon excitation by electromagnetic radiation, a plurality of dynodes that amplify said electrons by the secondary emission process, an anode that collects the amplified electrons to yield an output signal, electron-sensitive means disposed in the path of electron flow that yields electromagnetic radiation upon excitation by the electrons, and light pipe means for transmitting optical signals representative of said said electromagnetic radiation toimpinge upon said first means.
4. A heaterless cathode ray tube of the beam-index variety comprising an evacuated envelope having (1) a first section including an electron gun with a photon-sensitive source of electrons from which is derived an electron beam for scanning a target screen and (2) a faceplate section having associated therewith an electron-sensitive target screen responsive to the scanning action of the electron beam, the target screen having a pattern of periodically arranged strips for generating index signals to indicate the position of the electron beam on the target screen; in combination with (3) elongated light pipe means disposed so as to pick up and transmit optical signals emerging therefrom fall upon said photon-sensitive source of electrons thereby to provide the scannable electron beam.
5. The CRT of claim 4- wherein the elongated light pipe is comprised of a scintillator material transmissive of its scintillations and is positioned to be penetrated by the index signals along a substantial portion of its length thereby to generate optical signals in the interior of the light pipe which are transmitted to the exit terminal thereof in concentrated form.
6. A heaterless cathode ray tube comprising: an envelope including a target screen comprising means for generating a first and second index signal in response to excitation by the scanning beam indicative of the position of the scanning beam on the target screen; a first elongated light pipe for transmitting optical signals representative of said first index signal, a second elongated light pipe for transmitting optical signals representative of said second index signal; a first and second electron-emitting photon-sensitive element; means for positioning theexit terminals of said first and second light pipes so that the optical radiation emanating therefrom impinges upon said first and second photon-sensitive elements, respectively, thereby to provide a scannable electron beam; and means intermediate said elements and the target screen for modulating the scannable beam of electrons.
7. A beam-index cathode ray tube comprising a target screen and means including an electron gun for projecting an electron beam onto said screen, a photon-sensitive source of electrons in said electron gun from which the electron beam is derived, and screen having target elements disposed to be excited by the electron beam, an array of index signal generating elements disposed in register with the target element, said index generating elements being radiation emissive when bombarded by electrons thereby to indicate the position on the screen of said electron beam; in combination with a light pipe member with an exit termination disposed proximate said photon-sensitive source of electrons, so that radiation transmitted through light the pipe impinges upon said photon-sensitive source of electrons; said light pipe member further comprising a slab of scintillator material having a broad surface area disposed to be impinged upon and penetrated by the index signals over a substantial region thereof whereby scintillations are generated in the interior of the slab for transmission to said exit termination.
8. A beam index cathode ray tube comprising a target screen and means including an electron gun for projecting an electron beam onto said screen, a photon-sensitive source of electrons in said electron gun from which the electron beam is derived, said screen having target elements disposed to be excited by the electron beam, an electron permeable layer disposed rearwardly of said target elements, an array of index signal generating elements disposed rearwardly of said layer, said index generating elements being radiation emissive when bombarded by electrons thereby to indicate the position on the screen of said electron beam, anelectron permeable ion absorbing layer disposed on the back of said index signal generating element for suppressing the generation of spurious index signals; in combination with a light pipe member with an exit termination disposed proximate said photon-sensitive source of electrons so that radiation transmitted through the light pipe impinges upon said photon-sensitive source of electrons wherein said light pipe member also has an entrance terminal disposed to be impinged upon by the radiation emitted from the index generating elements whereby said radiation is transmitted through the light pipe to release electrons from said photon-sensitive source.
9. A beam index cathode ray tube comprising a target screen and means including an electron gun for projecting an electron beam onto said screen, a photon-sensitive source of electrons in said electron gun from which the electron beam is derived, said screen having target element disposed to be excited by the electron beam, and electron permeable layer disposed rearwardly of said target elements, an array of index signal generating elements disposed rearwardly of said layer, said index generating elements being radiation emissive when bombarded by electrons thereby to indicate the position on the screen of said electron beam, an electron permeable ion absorbing layer diaposed on the back of said index signal generating elements for suppressing the generation of spurious index signals; in combination with a light pipe member with an exit termination disposed proximate said photon-sensitive source of electrons so that radiation transmitted through the light pipe impinges upon said photon-sensitive source of electrons wherein said light pipe member comprises an elongated light pipe-scintillator disposed to be impinged upon by the radiation emitted from the index generating elements along its length, said light pipe-scintillator being further characterized i. in that it is capable of being penetrated by the index radiation thereby to generate scintillations in its interior region which are light piped to the exit termination.
10. A cathode ray tube comprising an envelope and a target screen within said envelope said screen comprising means for emitting a plurality of electromagnetic radiations designated x x upon excitation by a scanning beam of electrons; a plurality of spaced apart photon-sensitive means excited via each of said radiations that furnish electrons in different spatial groups designated y,, y and means within said envelope for amplifying, combining, and focusing the thusfurnished electrons thereby to provide the beam of electrons which is used to scan the target screen; including a plurality of light pipe members each having a relatively large entrance region and relatively small exit termination, the entrance region of each light pipe comprising a scintillator material having a broad surface region which is positioned to be impinged upon and penetrated over a substantial area thereof by a selected one of said radiations x x thereby to generate scintillations which are transmitted via light piping action to said exit termination in order to excite a selected one of said spaced apart photon-sensitive means.
11. A cathode ray tube comprising an envelope and a target screen within said envelope, saidscreen comprising means for emitting electromagnetic radiation upon excitation by a scanning beam of electron; photon-sensitive means excited via said radiation that furnish electrons; means within said envelope for amplifying and focusing said furnished electrons thereby to provide the beam of electrons which is used to scan the target screen; including a relatively small exit termination, said entrance region comprising a scintillator material having a broad surface region which is positioned to be impinged upon and penetrated over a substantial area thereof by said radiation thereby to generate scintillations which are transmitted via light piping action to said exit termination in order to excite said photon-sensitive means.