US2307209A - Electronic device - Google Patents

Description

Jan. 5, 1943. R. H. GEORGE 2,307,209

ELECTRONIC DEVICE Filed Dec. 21, 1939. 2 Sheets-Sheet 1 a T0 5011A RE WA v5 GENERA 70/? 3-12 MC.

-/2 MC INVENTOR.

VDfROS 05 H. GEO/26E A F 7 O1 EV Jan. 5, 1943. R. H. GEORGE 2,307,209

ELECTRONIC DEVICE Filed Dec. 21, 1939 2 Sheets-Sheet 2 A 7'0 TERMINAL 29 (FIG. I)

POSITIVE BIAS 'Vo/v ELECTRODE l9 0 L e =IIVITIAL PH07'0ELECTRI6 GEM/ND P TENTIAL VELOC/TYDl/E 7'0 1/6117 H v01 74 65 0120 VOLTAGE ALRUSS RES/570R 89 b q BIAS (F162) a 9 a f k} 1 l l q H l 1 1 Fr L 1 U U l U u U anny/v0 LE WAVE I NV EN TOR.

R0560 H. GEORGE BY M ATTORNEY.

Ii im. 5, 194

ELEWRQNKC DEVICE Roscoe H. George, West Lafayette, incl, asslgnor to Radio Corporation or erica, a corporation of Delaware Application December 21, 1939, Serial No. 310,363

12 Claims.

vention is concerned with a means and method of converting one form of energy into energy of another form or the invention is directed to the plification or intensification of energy of the se or approximately the same character.

Further, the present invention is concerned with a method and means particularly applicable to amplifying light energy occurring either in the visible or invisible portions of the spectrum to produce in amplified form light energy in the visible portion of the spectrum.

In a slightly modified form the invention is directed to a method and means for converting one form of energy, such as light image (either visible or invisible) into an electronic image which is intensified or multiplied so as to produce an intensified representation of either an electric or an optical form which is characteristic of the original form of energy.

As the invention will herein be described it will be seen that one form thereof is particularly concerned with the provision of a light amplifying device adapted to make visible objects normally invisible or to provide for the conversion of radiant energy of one form into energy of another form. In general, the present invention provides an electronic device wherein through the In its preferred form the invention comprises an electronic tube wherein one or more photosensitive elements are provided and in which suitable control of the release of photoelectrons is provided and wherein there is provided, in turn, suitable means for controlling the release of secondary electrons which are electronic replicas of the initial spatially coordinated photoelectric emission but in magnified form, it being understood, of course, that accurate focusing of the initially released electrons is maintained.

Through the use of suitably controlled generators or the like the released secondary electrons, produced from successive impacts of the released electrons upon a surface having a high secondary emission ratio, may be caused to initiate, on a suitable luminescent screen, visible light energy. Similarly, the electrons released by secondary emission may be caused to produce on a suitable mosaic electrode, arranged to be scanned electronically, an electrostatic replica of either the visible or invisible light image initially causing the release of primary photoelectrons. In the latter case, through scansion of the mosaic electrode by an electron beam or by a distributor of any suitable form there may be released to an external signaling circuit electrical energy representative of the activating radiant energy transformed into a wave train or series of signaling impulses.

To accomplish these results it will be appreciated that dynamic electronic multiplication (i. e. electron multiplication wherein the flow of primary and secondary electrons takes place along substantially the same path and in which the rimary and secondary electrons flow in substan tially the same, or in the case of some types of tubes in opposite directions) occurs within the tube so that an initially produced electronic image becomes substantially intensified prior to utilization for the ultimate production of an optical replica. In systems wherein dynamic electronic multiplication occurs the phenomena is usually associated with wave energy of alternating characteristic. In the present invention the time period of dynamic multiplication is preferably regulated by a controlling alternating current wave from which control potentials are applied at relatively rapid rates to regulate the periods of electron impact at predetermined areas within the tube whereat electron multiplication results because of secondary emission properties of the impacted areas.

Accordingly, among the objects of invention are included those of developing a secondary emission electronic image of any of the potential, current or charge types in a form which is substantially intensified as compared to that causing the primary emission electronic image; that of providing a suitable method and means for directly amplifying a light image; that of providing a suitable method and means for increasing the magnitude of electrostatic charges from which a wave train of signal energy representative of a light image are derived; and that of providing a simplified arrangement for converting energy of one form into energy of another form.

Still other objects and advantages of the invention will be found set forth in the description of the invention and also by the hereinafter appended claims when each is read in connection with the accompanying drawings wherein Figure 1 illustrates one form of alight amplifier tube particularly adapted for converting radiant energy or either a visible or invisible form into magnified radiant energy of a visible nature;

Fig. 2 represents a modification of the arrangement of Fig. I particularly adapted for use as an image scanning tube as useful in television systems;

Figure 3 illustrates in a schematic manner one of a number of suitable electrical circuits for deriving operating energy for controlling the operation of the tubes of either Fig. l. or Fig. 2.

Figure 4 represents diagrammatically the relationship between the accelerating alternating voltage and the biasing voltage applied to the photoelectrically active electrode element; and

Figure 5 represents in diagrammatic manner the relationship between the changes in control voltage between maximums and minimums and the frequency of the oscillator controlling the release of secondary electrons; and in this figure time is represented as the abscissa and the amplitude of the controlling generators as the ordinate values.

Referring now directly to Fig. 1 for a further understanding of the invention, there is provided an envelope ll having a front viewing window 13 and a rear viewing window It. The tube envelope II is suitably evacuated and contains therein the electrode elements l'l, id and 2i which are each in the general form of gridlike elements and which are preferably formed from a conducting mesh, later to be explained. Immediately in front of the rear viewing window I5 is still an additional electron accelerating electrode element 23'. This element it is in close proximity to the tube end wall it which is coated with a suitable luminescent material preferably having a relative short time lag. The short time lag screen prevents regeneration, as will later be apparent. Also, where desired, the electrode 23- may rest directly upon the luminescent target. It is desirable in some instances to support the luminescent screen upon a substantially transparent element positioned intermediate the tube end wall it and the electrode element 23 where it is desired to spray or deposit the screen externally of the tube blank and prior to assembly. By such construction it is easier to provide the luminescent material support element as a true planar structure even though the tube blank be slightly curved. Also, under some conditions where the time lag can be short, as will later be apparent, the element 23 may of itself constitute a conducting thermal type screen of either the metallic form or a carbonized woven or fabric screen of the general type already known and used in the art.

All of the electrode elements ll, it, 2! and 2d are arranged to connect to external circuits by way of the conducting leads 2%, 21!, 2i! and ti, respectively which may emerge from the tube wall through a common supporting press member held in a single evacuating stem. The electrode I9 is preferably formed as a conducting wire cloth of relatively fine mesh and is snitably photosensitived in a well known manner, e. g. by introduction of the photosensitive material in a vapor state with some suitably photoaeovaoa electrically active element. such as caesium, potassium or any other element found in the same group and series of the periodic series of the elements. The electrodes I1 and fl are also formed from conducting wires woven into a mesh but the mesh in the case of elements l1 and 2| is relatively coarse. The coarse mesh for the electrode ll, as will later be apparent, is for the purpose of preventing the absorption of any substantial amount of light which should reach the photosensitive mesh id and the coarseness of the mesh for the electrode 2| is for the purpose of preventing the absorption of electrons which are from time to time to pass therethrough after being drawn away from element It. The, light image which is to be amplified or converted from an invisible or visible form into an intensified visible form is directed by means of a suitable optical system it so as to impinge upon the photoelectrically activated meshlike conducting electrode l9.

To these electrodes there is preferably applied at the terminal point 21 a suitable positive voltage, varying for example between 30 and volts positive relative to ground. To the electrode N there is supplied, by way of the tank circuit 35 (usually comprising parallelly connected inductance and capacity elements) connected at one end thereof to the conducting terminal 2t and at the other end thereof to ground at 31, suitable high frequency energy of relatively high amplitude as compared to the voltage applied to the terminal 21 of the light sensitive electrode I9.

The spacing between the electrodes l! and It is somewhat critical, as will be appreciated from what is to follow. If it be assumed that the frequency of the energy supplied to the electrode element I! by way of the conductor 2% from the tank circuit 35 is of a frequency varying between 30 and 60 megacycles it will be appreciated that the geometry of the tube, if electrons which are released under the influence of light on the photosensitive electrode it are not to reach the elements I1, the electrode spacing must be so related to the frequency of the energy applied to the electrode and the electron transit time between electrodes it and N that an electron released from the photoelectrically active surface I9 and subjected to an acceleration in the direction of the electrode if by virtue of a predetermined portion of the positive half of the cycle of the high frequency energy applied thereto will move through a distance just slightly less than the distance between the electrodes l9 and I1. As the polarity of the high frequency energy supplied to the electrode W by way of the tank circuit at changes in direction toward the negative half of its cycle, it is, of course, immediately apparent that the positive voltage relative to ground applied to the photoelectrically active element Ill becomes effective to draw electrons in the space between the electrodes l1 and it over to the electrode is and the electrons so drawn back then strike the electrode Iii to release secondary electrons for each primary electron arriving at the surface Ill.

The number of secondary electrons released at each impact of electrons at the electrode It is, naturally, determined by the surface characteristic of the electrode l9. One important factor controlling the number of secondary electrons released per arriving primary electron is the value of the direct current bias applied to the elec-' aaoaoo trode" it at terminal 2i and also the amplitude trode i9). This is because these two factors determine the impact velocity of theelectrons upon trodes land it being or proper order (as above noted), it is readily apparent that released electhe surface is and the magnitude of the bias on electrode l9 relative to the amplitude of the applied alternating current wave on electrode ll determines the portion of the alternating current wave cycle at which it is possible to release secondary electrons from the surface it. Since the frequency of the alternating current wave applied to the electrode ll determines to a substantial extent the required spacing between electrodes ill and I9 it will be appreciatedthat an increase in the alternating current frequency permits closer electrod spacing and increases in frequency, (for constant electrode spacing) permits greater amplitudes of the alternating current and also higher bias on electrode l9 (due to decreases in electron transit time because of the shorter period control cycle) so that higher impact velocities at electrode i9 may result. The impact velocity in each instance is due, of course, both to the motion of the electrons provided by the alternating current applied at electrode ii and the acceleration provided by the positive bias on electrode 119.

By referring to Fig. 4 it will be seen that the high frequency voltage wave a at predetermined time periods overcomes the positive bias on the photosensitive element i9. Substantially no electrons leave the photosensitive surface ill when the high frequency voltage wave is negative relative to points I) or :1 because of the positive bias holding electrons to the surface it. Nominally, electrons would not leave the surface it) under light activation thereof except when the high frequency wave a was more positive than the bias voltage but with electrons released by light having some initial velocity (variable) with the color of the impinging light and determined in accordance with Plancks constant and the work function) this eifect is caused to take place in regions conventionally represented as h and d for monochromatic light.

It is thought that the only released photoelectrons which are effective to release secondary electrons upon returning to the surface It under the control of the alternating current wave supplied to electrode ii are those electrons which are released in the region schematically represented between points b and because those electrons released between 0 and d return to the surface i9 when the polarity of electrode li changes neg-l ative under the control of the alternating current wave in such a manner that secondary electrons cannot be released because there is a lack of any accelerating voltage between elements H and I9 at such times. These secondary electrons then are added to the primary electrons released at the instant under light activation. With the energy continuously applied to the electrode I! by way of the tank circuit 35, it is apparent that there will be an oscillation of both primary and secondary electrons back and forth in the space between electrodes l9 and H which takes place along substantially the same path so that those electrons which return to the surface 19 strike it electrode it and the spacing between the electrons Just fail to reach the element ii in the course of normal oscillation. After the electrons have oscillated through-the predetermined number of oscillations, for example, after a predetermined number of cycles of oscillations supplied to the electrode il in the space between the electrodes IQ and I! so as to release for each impact upon the electrode is secondary electrons, there is applied to the electrode element 2i by way of the terminal connection 29 a. suitable square topped voltage wave Whose, f q n is p ef ably from 10% to 20% of that of the frequency of the energy supplied upon the electrode ii. The energy from the square top wave generator operates to cause the electrode member 2! to be carried positive at the frequency of the square wave energy source connected at terminal 29 for periods when the energy applied is positive in sign and of suificient magnitude to overcome any applied bias. After a predetermined number of cycles of energy applied to the electrode i1, it can be seen that due to the geometry of the tube and the relatively close spacing between the electrode elements i9 and 2i, whatever electrons are arriving at the electrode ii! at that period of time when the electrode member 2i is carriedpositive will pass directly through these two electrodes and become subjected to an accelerating field toward the window i5 due to the potential applied to terminal 3| and the target screen 23.

The target or screen element 23 is preferably maintained at positive potential relative to ground, and at a voltage varying between 500 and 5,000 volts, so that whenever the electrode element it becomes positive it causes the electrons in the space between the electrodes l9 and IT to be drawn through it in order that they may impinge upon the target or screen 23. The electron fiow impacting upon the target element at relatively light velocity causes the target area to luminesce and to appear with intensity proportional to the impacting electron density. In this way the electrode element 2i functions in a nature somewhat similar to the functioning of the control grid in the usual type of vacuum tube amplifier in that this electrode element 2! determines in accordance with whether its potential is positive or negative relative to ground (this latter being a function of polarity of the square energy applied), whether or not electrons pass through the space or area of the tube between the photosensitive electrode [9 and the target electrode 23.

In order that the electrons initially released from the photoelectric element I9 may be maintained in the proper spatial relationship with respect to the light image which causes their initial release, a suitable electron focusing coil 39 is provided. This coil is arranged to extend longitudinally for substantially the complete tube length. By virtue of the produced electromagnetic fieldvof the coil 39 there is such a concentration of the electrons that the electrons are maintained, in motion under accelerating potentials, in such spatial relationship that the electron motion is along a path longitudinal of the tube ii. In this way the spatial position of the electrons within tube II will be exactly related to the spatial portion of the light points of the image in the tube window I3 which causes the initial release of the electrons. or course, it is apparent that there may be substituted for the electro-magnetic focusing coil 39 a suitable form of electrostatic focusing field which readily can be produced by positioning metal bands within the tube and applying suitable potentials thereto tive cathode I9 is photosensitized with materials highly sensitive in either an ultra-violet or infrared regions of the spectrum, the tube E9, of course, provides for the conversion of radiant energy normally invisible into visible radiations. In cases where visible light is focused upon the photosensitive cathode l9 the device operates to produce magnified light representations of that optical image initially impressed upon the photosensitive cathode.

The arrangement of the optical system shown at 83 herein, it is to be appreciated, is only a schematic showing of a complete optical system. It is usually preferable to focus an erect image of the object to be viewed upon the photosensitive cathode l9 so that an erect image is pro- Jected upon the screen or target electrode 23. This then precludes the necessity of providing an optical system for viewing the screen 23 although it is, of course, to be appreciated that where an optical system for inverting the image is used in connection with viewing, the image i'ocussed upon the photo cathode I9 is preferably to be inverted. However, where electrostatic focusing systems are utilized it is possible to obtain cross-over of the image directly within the tube through the use of suitable potentials upon the several focusing electrodes. In this event it will be appreciated that in a case where the electrostatic focusing system provides for crossover in that portion of the tube between the cathode element l9 and the target element 23 it is possible to project an inverted image upon the photosensitive cathode and still produce upon the target electrode 23 an erect image, it being assumed that there will be no inversion of the image in the area between the cathode electrode I9 and the accelerating electrode Ill.

Still further, it is frequently desirable to provide a combination of electromagnetic and electrostatic focusing means for the electrons flowing within the tube in which event the magnetic focusing would usually be provided for that portion of the tube between the electrodes l9 and i1 and the electrostatic focusing system would be utilized for that portion of the tube upon which the produced image becomes visible.

As was above explained in order to improve the operation there is applied to the controlling electrode 2!, by way of the terminal connection 29, a voltage of substantially square-top wave form. The general form of this wave, in contrast to a substantially sine wave characteristic, oi the voltage applied to the terminal 25 of the electrode IT, has been shown and sketched adjacent the terminal 29. It can be appreciated from what was above explained with the frequency of the square-top wave applied to the terminal 29 being about /20 to that 01' the alternating current applied to the electrode ll, 75

that during each cycle of the square wave the high frequency wave will pass through several complete cycles, varying in number between 5 and 10 in accordance with the chosen ratio above assumed. The voltage variations from a minimum to a maximum of the square wave, it will be appreciated from the designations on the wave form shown adjacent the terminal 29 and also from Fig. 5, causes the voltage applied to the photoelectrically responsive electrode I9 during the positive half cycles to be relatively negative with respect to the element 2| so that the element 2| functions, in effect, as a positive grid element between the photoelectric element l9 and the target or screen electrode 23 to permit electrons to flow through the tube envelope II in the space between the electrodes is and the target 23.

While many forms of suitable circuit arrangements may be provided for obtaining this square wave one suitable form is shown by Fig. 3 where the tube M is connected as an oscillator with the anode or plate electrode 43 and the grid or control electrode 45 connected to the end terminals of the usual tank circuit M. The tube cathode element 49 is then connected at a central point in the tank circuit. This circuit, it can be seen, is a substantial duplicate of the well-known Hartley form of oscillator and requires no further explanation.

The amplitude of the oscillations developed by the oscillator tube ll are relatively high. These oscillations then are directed by way of the coupling condenser 5| (although other forms of coupling might be used) to energize the control electrode 53 of an amplifier 55. Between the control electrode 53 and the cathode 51 of the amplifier the usual leak resistor 59 is provided. The tube is of such characteristics that because of the substantial amplitude of the oscillations developed from the oscillator il the tube will saturate at predetermined time periods corresponding to a predetermined voltage output from the oscillator 4| and thus produce the square top wave form indicated on Fig. 5. Output energy from the amplifier 55 is fed from the plate or anode electrode 6| which is energized from a suitable source of positive voltage through a load resistor 63 so that output energy flows through conductor 65 which connects to terminal point 29 in Fig. 1. The values of inductance and capacity of the tank circuit M for the oscillator 4| are suitably chosen so that the natural period of oscillation of this tube corresponds to the assumed frequency varying between 3 and 12 megacycles, which was above assumed as being the frequency applied to the terminal point 29.

Suitable bias for the grid or control electrode Ml of the oscillator 4| is provided by way of the biasing source 6'! and suitable anode potential for the oscillator tube M is provided by the source of voltage connected at terminal point 69 and poled positively relative thereto.

In a modification of the invention, shown by Fig. 2. which is particularly applicable to a transmitter type tube, an end window 13 through which an optical ,image is directed by means of a suitable optical system 33 imilar, for example, to that shown by Fig. 1 is formed as a part of the tube envelope II. The optical image is projected internally of the tube envelope H so as to impinge upon the portion of a double mosaic electrode 15 which faces toward the end window 13. The double mosaic electrode 15 has that surface i'i thereof which faces the end window it formed from material which is both photosensitive and capable of copiously emitting secondary electrons. The rear side 19 of the double mosaic electrode 13 is formed preferably from material in which a greatly reduced number of secondary electrons as per impinging primary are released. Such material, for example, may be various forms of carbonized surfaces and the like which, while conducting are poor secondary emitters. This type of electrode, it can be seen, will serve the purpose of enabling the element to acquire a negative charge from the scanning beam, as later will be explained. The general structure of the double mosaic electrode 15 may be substantially like that which has already been described in the art by patents granted to L. E. Flory and W. Hickok, Nos. 2,045,984 and 2,047,369, respectively. Such an electrode is formed from a conducting mesh of which the variou wires of the mesh are insulated, such as by an enameled coating, to provide thereover a desired thickness of insulating coating. The interstices of the mesh are then packed in suitable manner, as already explained in the art, with conducting material such, for example, as a material which may be formed from an amalgam of silver. The conducting packings are pressed into the interstices of the mesh-like conductor, after it has been suitably enameled, so that the conducting material may have its end portion which faces toward the end viewing window 13 suitably photosensitized with caesium, potassium or other suitable photoelectric material, depending upon the response characteristic desired and depending upon whether or not the device is to be most highly sensitive to light from the visible or invisible portions of the spectrum. In this way high secondary emission is obtained from photosensitized surface ll of the double mosaic electrode. The rear surface 19 of the conducting plug members of the double mosaic is preferably suitably carbonized, as above suggested, in order that reduced secondary emission may result.

The complete double mosaic electrode then has the conducting mesh connected to a suitable terminal point ti which may be grounded at 83. This is done in order to maintain the mosaic at a definite reference potential.

Elosely adjacent the end window i3 there is positioned an electrode 85 of relatively coarse mesh corresponding substantially to the electrode iii of Fig. 1. This electrode connects to the terminal point 8i! which connects to the tuned circuit ti and thence through resistor 89 to ground it through a portion of battery or other voltage source til, as will hereinafter be more fully described.

hi; the opposite end of the tube ii there is provided a suitable means for developing a cathode ray beam which is to scan the rear surface it of the conducting elements of the double mosaic which have relatively low secondary emission. lln order to develop this electron beam there is provided an electron emitter, a suitable control electrode and an accelerating and focusing anode, all of which elements are conventionally represented and are well known in the art. Uh the inner surface of the conical portion tube there is provided usually a conducting coating it which is to serve as a second anode of the tube and which is maintained at a relatively high potential with respect to the first anode of the electron gun 93 and also at a further higher potential relative to the emitting cathode.

In order to deflect the cathode ray beam developed from the gun 93 and to cause it to traverse the mosaic electrode 15 along bi-directional paths suitable deflecting means, such as the conventionally represented electrostatic defleeting plates 96, 91, and 98 and 99 are provided, although it is obvious that electromagnetic deflection may be substituted in whole or in part.

With the rear surface 19 of the conducting elements of the double mosaic 15 having been suitably treated so as to produce relatively low secondary emission, it will be appreciated that the electrons from the scanning beam developed from the electron gun 93 may cause the conducting elements to acquire a charge so as to be at a. potential varying, for example, between ground potential and a limiting value somewhat negative with respect to ground. The limiting value may be considered as being dependent upon a number of quantities, such as the beam velocity, the location of the bias element 82, the secondary emission from the surface 79 and the general geometry of the tube. Under these conditions, it will be understood, that the beam current of the cathode ray beam in excess of the amount necessary to charge the elements 19 is returned to the conducting coating 95 by virtue of the negative potential created upon the mosaic electrode, which potential develops because of impact of the scanning beam.

In this arrangement the battery or bias unit 82, which is an element preferably having low distributed capacity to ground, is usually connected intermediate the second anode 95 and the output resistor Bill which connects to ground. With this connection the bias unit is poled with its positive terminal connecting to the anode 95. It is possible, however. under some conditions of operation, to connect the bias unit 82 between the mesh of the double mosaic and ground at 83. This form of connection, however, usually requires the bias source to be poled so that the positive terminal will then be connected to ground which will maintain the mesh 15 negative relative to the anode 95.

Any current which flows between the mosaic surface 59 and ground 83 must flow through the resistor NH and provide the signal current which is to be fed to the amplifier (not shown but indicated).

In order to multi ly the photoelectric current released from the p otosensitized ends ll of the conducting pin members forming the double m0- saic ii a high frequency voltage of a value varying between 30 and 60 megacycles, for example, is supplied from the source 92 and the tuned circuit 9i, so as to be applied to the electrode 85 by way of the terminal connection Bi and to be superimposed upon a pulsating direct current voltage which appears across the resistor 89. The tube 9% which has its output circuit so arranged as to include the resistor 89 has provided as part of its input circuit the tuned circuit comprising inductive and capacitive elements tuned to the frequency of the source 802, conventionally represented. The coarse mesh electrode 85 has preferably also been treated so as to prevent secondary emission therefrom.

Whenever the tube 94 is passing a maximum current the voltage drop occurring across the resistor 89 is considerably greater than that of the bias voltage applied to the electrode 85 from that portion of the source 86 which is connected be tween the electrode 85 and ground 83.

As was above explained, in connection with Fig. 1, whenever the various portions and the frequency of the oscillator 92 are properly adjusted the photoelectrons which are released from the photoelectric coating 11 on the conducting pins of the double mosaic electrode 15 are released during the interval from a to b as shown particularly in connection with Fig. 5. It will be appreciated that the electrons will be drawn or driven toward the electrode element 85 until the point e in the cycle of the high frequency wave is reached, after which the opposing voltage causes the electrons to be decelerated until their motion is substantially arrested at a point conventionally represented on Fig. 2 as s, after which the combined electrical fields acting within the tube cause the electrons to be driven back along the path conventionally indicated by Fig. 2 until they impinge upon the photoelectric surface 11 with sumcient energy to cause the release of secondary electrons.

If the geometry and the parameters of the system have been properly adjusted the initial electrons will arrive back at the mosaic electrode iii at point a on the high frequency wave as indicated by Fig. 5, and the cycle will be repeated. After the secondary emission current has been built up over a number of cycles of the high frequency wave, as indicated by Fig. 5, the electrons must be drawn oil to the electrode element 85 before the image is destroyed by space :charge effects and also to allow for any changes in the optical image. In order to do this the current flowing through the resistor 89, which is to furnish bias on element 85, should be reduced to zero or substantially thereabouts periodically by means of the lower frequency voltage from the oscillator Hi2 driving the control electrode of the tube M to cut-ofi. This allows the voltage from the power supply or the source at to cause the electrons to reach the electrode element 85.

In a case where, due to the coarseness of the mesh of the electrode element 85, electrons tend to pass through the mesh toward the end wall 13 of the tube II such electrons may be collected by providing intermediate the electrode 85 and the end wall 13 of the tube still an additional electrode 88 to which a positive potential is continuously applied from a source 88'. However, it will be seen andappreciated that the greater the number of electrodes in the direct path of the optical image the greater will be the light lossand the greater the distortion. Therefore, it is usually desirable to make the mesh 88 slightly coarser than element 85 but where possible the inclusion of the additional electrode 88 should be avoided. In this connection, however, it can be seen that the auxiliary electrode 88 is so far out of focus that its presence is of relatively minor effect on the optical image cast upon the surface 11. Of course, it will be seen that in a short tube where element 85 is near the end wall I3 the inclusion of element 88 will tend to increase the capacity and thus perhaps waste power but where space requirements permit this capacit may be reduced by lengthening the tube and permitting element 88 near the face 13.

From what has been herein explained, therefore, it can be seen in connection with the modification of Fig. 2 that a suitable high frequency is applied to the electrode member 85 by way of the suitable source of alternating current 92 which is preferably of the order of 30 to 60 megacycles. Further, it can be seen, that due to the spacing of the double mosaic electrode 15 and the electrode element 85 all of the electrons aaomoa released by light falling upon the photosensitized ends 11 of the conducting plugs of the double mosaic will be caused to be oscillated in the space between these electrodes in substantially the same manner as was described in connection with the oscillation of electrons between the elements I 9 and i! of Fig. 1. These electrons in their oscillations do not ordinarily reach the electrode t5 unless that electrode acquires a positive potential due to the source 84 as happens at certain intervals in the operation cycle, as above explained. For each time period while the electrons are oscillating in the space between the double mosaic l5 and the electrode 85,, there are released for each impact of the electrons upon the photosensitized surface 11 of the double mosaic additional electrons in the form of secondary electrons. Whenever the electrons are released finally and subjected to a positive potential of relatively long period on the electrode 85 the electrons are accumulated by electrode elements 85 or 88 and passed to ground. The signals which are developed within the system and which signals are to control the amplifier connected to the upper end of the resistor Iill are such signals as result from the electrons reaching the conducting coating 95. It can be seen, therefore, that the signal current from this coating is of such a direction that an increase in light on the photosensitive surface 11 tends to cause a decrease in the signal current. In cases where it is desired that an increase in light shall produce an increase in the signal current this eflect may be obtained by an additional amplifier stage. In addition, it will be appreciated that one of the primary advantages of the image scanning system described in connection with the arrangement of Fig. 2 is that the output energy includes essentially the direct current component which is not realized in the case of many of the presently known forms of electronic light translating systems.

Having described my claim is:

1. The method of intensifying the effect of an optical image which comprises photoelectronically converting an optical image into an electronic replica, developing an alternating current field to oscillate the produced electronic replica between predetermined planes for a selected time period and to produce at the end of the selected period an intensified electronic replica, arresting the oscillation of the electrons, collecting the entire oscillated and intensified electronic image at a plane spaced from one of the first-named planes immediately subsequent to the period of arrest, and cyclically shifting the control to cause the electron flow to be sequentially oscillated and arrested and collected.

2. The method of intensifying the effect of an optical image comprising photoelectronically converting an optical image into an electronic replica, developing an alternating current field to oscillate to produce electronic images between predetermined planes for a predetermined time period, momentarily arresting the oscillations, and then collecting the oscillated electronic images during the period of arrested oscillation at a utilization plane spaced from and parallel to one of the first-named planes to produce thereat an intensified representation of the entire original electronic image.

3. The method of intensifying the effect of an optical image directed upon an electronic tube having a photo-sensitive and secondary electron invention, what I electrode element to receive the light image which comprises the steps of directing the optical image upon the light sensitive electrode element for photoelectronically producing an electronic replica of the optical image, applying a high frequency alternating electrostatic field to the developed electronic image to cause the electronic replica to oscillate between predetermined planes to produce dynamically electron multiplication of the developed electronic image at the electrode element only, subjecting the cally multiplied electronic image to a second electric field pulsating at a rate substantially less than that of the first alternating field to arrest dynamic multiplication and to simultaneously release the dynamically multiplied electronic image, and directing the released dynamically multiplied electronic image. at each period of release of the dynamically multiplied image, to an image utilization plane spaced from the first named planes.

i. A device for intensifying the effects of an optical image comprising photoelectric means for converting an optical image into an electronic replica, electrode means spacially positioned to receive the electronic replica, means for applying operating potentials between the photoelectric means and the said electrode means to oscillate the electronic replica between the said electrode means and a plane spaced a predetermined distance therefrom and to produce electron multiplication by dynamic action of the electronic.

replica impacting the said electrode means, means for controlling the application of the operating potentials to cause the electron multiplicaticii to continue for a predetermined time interval and thereby to produce an intensified representation of the initially developed electronic replica, and means to control the applied potentials following predetermined time periods to interrupt the said electron multiplication, and means to collect the intensified electronic image.

5. An intensifying device for the conversion of optical images comprising secondary electron emissive photoelectric means for converting an optical image into an electronic replica, a plural ity of parallel spaced electrodes including said first named means, means for developing an alternating current field between said electrodes to oscillate the produced electronic replica between said electrodes for a period of time to produce secondary electrons at said first means only, and means for collecting the oscillated electronic images in a plane parallel to and spaced trom one of said electrodes to concurrent- 1y produce thereat an intensified representation of the entire original electronic image.

6. An electronic device for intensifying the efiect of an optical image comprising a secondary electron emissive photosensitive electrode element to receive the light image and to produce an electronic replica of the optical image, a second electrode positioned parallel to and spaced from said first electrode, means for applying a high frequency alternating electrostatic field be tween the photosensitive and second electrodes to cause dynamically electron multiplication of the developed electronic image at the first electrode element only, a targetelectrode positioned outside the applied high frequency field, means positioned between the target electrode and said first electrode for subjecting the dynamically eiectron multiplied electronic image to a second alternating electrostatic field pulsating at a rate substantially less than that of the first alternating field to release the dynamically electron multiplied image, and means for directingand focusing the entire released dynamically electron multiplied electronic image upon the target electrode at each period of release of the dynamically multiplied image.

7. A device for intensifying the effect of an optical image which comprises secondary electron emissive means for photoelectronically converting an optical image into an electronic current replica, means including said first means for concurrently and dynamically electron multiplying the entire electronic current image for a predetermined time interval, means for focusing the original electronic image and to dynamically electron multiply the electronic current image during the period of image multiplication, means for developing at predetermined time intervals an electronic field to release the entire dynamically electron multiplied image, and means to simultaneously focus and direct the entire released image on to a utilization electrode.

8. An electronic device for intensifying the effect of an optical image comprising a light sensi tive electrode capable of emitting secondary electrons, means for projecting and focusing an optical light image upon the electrode to produce an electronic current image replica of the optical image by the emission of photoelectrons, a grid electrode positioned parallel to and spaced from the light sensitive electrode, means for applying a first alternating electrostatic field of high frequency between the light sensitive electrode and the grid electrode to cause the emitted photoelectrons to repeatedly bombard only the light sensitive electrode for a predetermined length of time to produce secondary electrons and dynamic multiplication of the developed electron current image, means for subjecting the dynamic multiplied electronic image to a second alternating electrostatic field having a frequency substantially less than that of said first electrostatic field to arrest dynamic multiplication of the electronic image after the predetermined length of time and to simultaneously utilize the dynamically multiplied electronic image.

9. An electronic device for intensifying the effect of an optical image comprising a light responsive electrode capable of emitting secondary electrons, means for projecting and focusing an optical light image upon the electrode to produce an electronic image replica of the optical image by the emission of photoelectrons, a grid electrode spaced from and positioned parallel to the light responsive electrode, means for applying an alternating electrostatic field of high frequency between the light responsive electrode and the grid electrode, the intensity and frequency of the electrostatic field being such as to cause the emitted photoelectrons to repeatedly bombard the light responsive electrode for a predetermined number of times to produce secondary electrons and dynamic multiplication of the developed electron image at the light responsive electrode only and to prevent the electrons from reaching the grid electrode, means for subjecting the dynamic multiplied electronic image to a second electrostatic field pulsating at a rate substantially less than that of said first electrostatic field to arrest dynamic multiplication of the electronic image after the predetermined number of bombardments, and means for collecting the dynamically multiplied electronic image simultaneous with the arrest of dynamic multiplication.

10. An electronic device for intensifying the efiect of an optical image comprising a photosensitive electrode capable of emitting secondary electrons, means for projecting and focusing an optical light image upon the electrode to produce an electronic current image replica of the optical image by the emission of photoelectrons, a first grid electrode spaced from and positioned parallel to the photo-sensitive electrode, means for applying an alternating electrostatic field of high frequency between the photo-sensitive electrode and the grid electrode, the intensity and frequency of the electrostatic field being such as to cause the emitted photoelectrons to repeatedly bombard the photo-sensitive electrode only for a predetermined number of times to produce secondary electrons and accordingly dynamic muitiplication of the developed electron image at the photo-sensitive electrode only and to prevent the electrons from normally reaching the grid electrode, a second grid electrode positioned on the opposite side of the photo-sensitive electrode from said first grid electrode, means for subjecting the dynamic multiplied electronic image to a second alternating electrostatic field having a frequency substantially less than that of said first electrostatic field by applying the second field to said second grid electrode to arrest dynamic multiplication of the electronic image after the predetermined number of bombardments, and means including said second field for proiecting the dynamically multiplied electronic image upon a target electrode simultaneous with the arrest of dynamic multiplication.

11. An electronic device for intensifying the efiect of an optical image comprising a photosensitive electron storage electrode capabie oi emitting secondary electrons, means for projecting and focusing an optical light image upon the electrode to produce an electronic image replica of the optical image by the emission of photoelectrons, a grid electrode positioned parallel to and spaced from the storage electrode, means for applying an alternating electrostatic field of high frequency between the storage electrode and the grid electrode, the intensity and frequency of the electrostatic field being such as to cause the emitted photoelectrons to repeatedly bombard only the storage electrode for a predeaaaaaa termined length of time to produce dynamic multiplication of the developed electron image at the storage electrode, means for subjecting the dynamic multiplied electronic image to a second alternating electrostatic field having a frequency substantially less than that of said first electrostatic field to arrest dynamic multiplication of the electronic image after the predetermined length of time, means including said second field for collecting the dynamically multiplied electronic image upon the grid electrode simultaneous with the arrest of dynamic multiplication, and means for utilizing the intensiiielg charge image produced on the storage elecro er 12. An electronic device for intensifying the efiect of an optical image comprising a photosensitive electron storage electrode capable of emitting secondary electrons, means for projecting and focusing an optical light image upon the electrode to produce an electronic image replica of the optical image by the emission of photoelectrons, a grid electrode spaced from and positioned parallel to the storage electrode, means for applying an alternating electrostatic field of high frequency between the storage electrode and the grid electrode, the intensity and frequency of the electrostatic field being such as to cause the emitted photoelectrons to repeatedly bombard the storage electrode for a predetermined number of times to produce dynamic multiplication of the developed electron image at the storage electrode only and to prevent the electrons from normally reaching the grid electrode, means for subjecting the dynamic multiplied electronic image to a second electrostatic field pulsating at a rate substantially less than that of said alternating electrostatic field to arrest dynamic multiplication of the electronic image after the predetermined number of bombardments,'means for collecting the dynamically multiplied electronic image upon the grid electrode simultaneous with the arrest of dynamic multiplication, and means for scanning the storage electrode to produce an intensified image signal output in an external circuit.

ROSCOE H. GEORGE.

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