Charge image storage method and apparatus

Abstract

The information stored on the dielectric target of a bistable storage tube is read out nondestructively employing a pulsed electron beam. The electron beam is turned on for a period having a duration less than necessary to change a given area of the target from one stable stored potential to another, while the period between pulsations is long enough so the tube's flood beam can return a given area to its original stored potential..Iadd.

I claim: 
     
       1. Charge image storage apparatus comprising: a storage target having capacitance for storing a charge pattern,   first means for bombarding such storage target with a first beam of electrons capable of causing secondary emission from selected areas from said storage target upon which said beam is directed for changing the voltage at such selected areas to store information,   second means for bombarding the storage target with a lower velocity flood beam of electrons acting to drive areas of said target towards one of two stable potentials depending upon information stored thereon by said first means for the purpose of holding such information on the target,   means for modulating said first beam to read out stored potential information located at a selected area of said target at which the first beam is then directed including means for .Iadd.independently .Iaddend.pulsing said first beam, wherein each pulsation thereof has a duration less than necessary to change such selected area from one said stable potential to another, the said flood beam driving said area back to its stable potential during the time between pulsations in order to retain such stable potential of such area, .[.and.]..Iadd.   means for systematically scanning said first beam of electrons, during read-out, over areas of the target where information is stored, and .Iaddend.   means coupled to said target for detecting a read-out signal.   
     
     
       2. A charge image storage apparatus comprising: a storage target for storing a charge pattern,   means for bombarding said storage target with an electron beam having a velocity capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas for storing information, and for bombarding sasid storage target with a beam of electrons for reading out stored information at a selected area of said target at which such beam is then directed, including means for .Iadd.independently .Iaddend.pulsing said beam during read-out, .[.and.]..Iadd.   means for systematically scanning said beam of electrons, during read-out, over areas of the target where information is stored, and .Iaddend.   means for directing a flood beam of electrons at such target for driving areas of such target towards one of two stable potentials by continued secondary emission from areas where information has been previously stored by secondary emission and by driving such target negative in areas wherein information has not been previously stored by secondary emission,   wherein such pulsation during read-out has a duration less than necessary to change a selected area from one stable potential to another, the flood beam of electrons driving such area back towards its stable potential in order to retain such stable potential of such area.  .[.3. The apparatus according to claim 2 wherein such pulsation is periodic and the period between successive pulsations is sufficient for said flood beam to retain the area being read out at its stored potential by driving such area entirely back to its normally stored potential whereby the sequence of pulsations does not drive such area from one stable potential to   
     
     
        another..]. 4. The apparatus according to claim 2 wherein said storage target comprises a photosensitive storage dielectric such that information may be stored thereon by means of a light image.  .[.5. The apparatus according to claim 2 wherein areas of said target wherein information is stored are systematically scanned during read-out with a beam of electrons..]. .[.6. The apparatus according to claim 5 including detection means coupled to said target for providing a read-out signal corresponding to said pulsations and indicative of information stored on the systematically scanned areas of said target, and including a second charge image storage apparatus comprising a storage tube disposed at a location remote from said first mentioned charge image storage apparatus, and   communication means between the first mentioned charge image storage apparatus and the charge image storage apparatus at the remote location including means for synchronizing the systematic scan at both such locations, such communication means coupling the output from the detection means of the first mentioned charge image storage apparatus to the second charge image storage apparatus for storing apparatus for storage at the latter location..]. .[.7. The apparatus according to claim 2 wherein the time duration, t, for a pulsation is less than the product of the voltage at the first crossover point in the secondary emission characteristic of the target and the capacitance of a target area read out, said product being divided by the sum of the reading beam current multiplied by (1 minus the secondary emission ratio for the reading beam) and the flood beam current multiplied by (1 minus the secondary emission ratio for the   
     
     
        flood beam)..]. 8. The apparatus according to claim .[.7.]. .Iadd.30 .Iaddend.wherein said pulsation is repetitive and the period between pulsations is greater than the product of the voltage at the first crossover point in the secondary emission characteristic for the target and the capacitance of the target area being read out, said product being divided by the floor beam current multiplied by (1 minus the secondary 
     
     
        emission ratio for the flood beam). 9. The apparatus according to claim .[.7.]. .Iadd.30 .Iaddend.wherein said pulsation is repetitive and the period between pulsations is greater than the product of a voltage, V, and the capacitance of the target area being read out, said product being divided by the flood beam current multiplied by (1 minus the secondary emission ratio for the flood beam), wherein the voltage, V, is the voltage actually reached by the target area being read out during the time, t. 
     
     
            Charge image storage apparatus comprising: a storage target including a photosensitive storage dielectric of phosphor material,   a first electron gun for bombarding said storage dielectric and writing information thereon during a writing mode with a first beam of electrons capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas toward a more positive value for thereby storing information,   flood gun means for bombarding the storage dielectric with a flood beam of low velocity electrons to cause continued secondary emission from said storage dielectric in the region where said first beam has been directed in its writing mode while maintaining other regions negative for providing two stable dielectric potentials on said target,   said first electron gun including a control grid having read-out means coupled thereto for .Iadd.independently .Iaddend.modulating said first beam in a reading mode such that said first beam emits regular pulsations of electrons, each pulsation having a duration less than necessary to change a selected area from one stable potential to another during read-out of stored information, said flood gun producing a flood beam driving the area read back towards its stable potential, and   signal plate means coupled to said target for providing a read-out signal,   said charge image storage apparatus being provided with deflection means and scanning signal generator means coupled to said deflection means to cause said first electron beam from said first electron gun to systematically and periodically scan during a reading mode the areas of   
     
     
        said target where information is stored. 11. The apparatus according to claim 10 further including amplifier means coupled to said signal plate means for receiving the read-out signal, pulse stretching means coupled to receive the output of said amplifier means for increasing the duration of pulsations received by said amplifier means indicative of information stored on said target,   mixing means for mixing said stretched pulsations with synchronization information from said scanning means,   a storage tube at a location remote from said charge image storage apparatus,   transmission means between said mixing means and said storage tube at said remote location,   scan synchronization means coupled to said transmission means at said remote location causing a systematically and periodic scan in said storage tube synchronized with the systematic and periodic scan in said charge image storage apparatus, and   means applying the pulsations from said transmission means to said storage tube as a writing input thereof so that information corresponding to the bistable images in said charge image storage apparatus is written in said   
     
     
        storage tube. 12. The apparatus according to claim 11 further including a 
     
     
        bandpass filter in cascade with said transmission means. 13. A method of reading information from charge image storage apparatus including a dielectric storage target, a high velocity electron beam means directing a high velocity beam at said storage target, a low velocity flood gun means directed at said storage target for retaining information thereon, and means coupled to said target for providing a read-out signal, said method comprising: directing a high velocity beam from said first electron gun at a particular area of said storage target for reading information from the same,   .Iadd.independently .Iaddend.pulsing said electron beam from said first electron gun with a pulse having a duration less than necessary to change an area being read out from one stable potential to another such stable potential,   repeating such pulse with a frequency such that the period between pulses is sufficient for said flood beam to retain such area at a stored potential value by driving such area back towards its stored potential, .[.and.]..Iadd.   scanning said electron beam in a regular pattern across the areas of said target storing information at the same time such beam is pulsed, and .Iaddend.   deriving from said means coupled to said target, read-out pulsations corresponding to pulses applied to said first electron gun and indicative of the polarity of stored information.  .[.14. The method according to claim 13 further including scanning said electron beam in a regular pattern across the areas of said target storing information at the same time such beam is pulsed..]. .[.15. The method according to claim 13 wherein the duration of a pulse is less than the product of the voltage at the first crossover point in the secondary emission characteristic of said target and the capacitance of the area of said target being read out, said product being divided by the sum of the first beam current multiplied by: (1 minus the secondary emission ratio for the beam from the first electron gun), and the flood beam current multiplied by (1 minus the secondary emission ratio for the flood beam) and wherein the period between pulses is greater than the product of the voltage at the first crossover in the secondary emission characteristic of the target and the capacitance at the area being read out, said product being divided by the flood beam current multiplied by (1 minus secondary emission ratio for the flood beam)..].   
     
     
            The method of claim .[.15.]. .Iadd.31 .Iaddend.wherein said electron beam is scanned in a regular pattern and wherein the duration of pulsation of said beam is lengthened and the period between pulses is shortened as the beam scanning rate is increased. .Iadd. 17. Image storage apparatus comprising: a tube adapted to store an image, said tube including a storage target and means for directing an electron beam toward said target for reading out stored information at selected areas of said target and including means for independently pulsing said beam during read-out, wherein the duration of a pulsation is less than would cause stored image information to be removed and new information written,   means for systematically scanning said electron beam, during read-out, over areas of the target where information is stored,   means coupled to said target for providing a read-out signal corresponding to said pulsations and indicative of information stored on the systematically scanned areas of said target,   utilization apparatus for providing a representation of information stored on the systematically scanned areas of said target, and   communication means between said means for providing a read-out signal and said utilization apparatus for coupling the output from the means for providing a read-out signal to said utilization apparatus. .Iaddend..Iadd. 18. The apparatus according to claim 17 further including means for synchronizing the systematic scan of the areas of said target where information is stored and the operation of said utilization apparatus for providing a representation of the information stored. .Iaddend..Iadd. 19. The apparatus according to claim 18 wherein said means for directing an electron beam at said target includes an electron gun and said means for pulsing said beam includes a control grid for said gun and means coupled to said control grid providing a control input for modulating said beam with regular pulsations. .Iaddend. .Iadd. 20. Image storage apparatus comprising:   a tube having storage target, and an electron gun for bombarding said target with a narrow beam of electrons, said electron gun including a control grid provided with an input for independently modulating said beam such that said beam emits regular pulsations of electrons, each pulsation having a duration less than would cause removal of information stored on said storage target,   means coupled to said target for providing a read-out signal,   scanning means for causing said electron beam to systematically and periodically scan areas of the target where information is stored and is to be read out,   utilization means for providing a representative of information stored on systematically scanned areas of said target,   transmission means between said signal plate means and said utilization means,   and scan synchronization means coupled to said scanning means and to said utilization means for synchronizing operation of said utilization means with a systematic and periodic scan of the electron beam. .Iaddend..Iadd. 21. The apparatus according to claim 20 wherein said utilization means comprises a cathode ray tube having deflection means and adapted to have the electron beam thereof deflected under the control of said synchronization means substantially in step with the first mentioned beam of electrons from said electron gun. .Iaddend. .Iadd. 22. Image storage apparatus comprising:   a storage target,   means for bombarding said storage target with an electron beam for reading out stored information at selected areas of said target at which such beam is then directed including means for independently pulsing said electron beam, wherein each pulsation thereof during normal read-out has a duration less than would remove the stored information, and   means coupled to said target for detecting a read-out signal in response to pulsation of said beam,   wherein said charge image storage apparatus is provided with deflection means for causing systematic scan of said electron beam over areas of the target where information is stored and which it is desired to read out. .Iaddend. .Iadd. 23. The apparatus according to claim 22 including means for causing a beam of electrons to bombard said target for storing information on said target. .Iaddend..Iadd. 24. The apparatus according to claim 22 wherein said storage target comprises photosensitive material such that information may be stored thereon by means of a light image. .Iaddend..Iadd. 25. The apparatus according to claim 22 wherein said means for bombarding said storage target with an electron beam comprises an electron gun and wherein said means for pulsing said electron beam comprises a control grid for said electron gun having means coupled thereto for modulating said beam with regular voltage pulsations. .Iaddend. .Iadd. 26. The method of reading information from an image storage apparatus including a target, means for directing a beam of electrons at said target, and means coupled to said target for providing a read-out signal, said method comprising:   directing a beam of electrons from the first mentioned means at a particular area of the target from which it is desired to read information,   independently pulsing said electron beam with a pulse duration less than would remove the stored information from the target,   scanning the electron beam in a regular pattern across areas of the target storing information at the same time the beam is pulsed, and   deriving, from said means coupled to said target, read-out pulsations corresponding to pulses applied to the beam. .Iaddend. .Iadd. 27. The method according to claim 26 further including reproducing the stored information at a second location in response to the read-out pulsations derived from said means coupled to said target. .Iaddend. .Iadd. 28. A charge image storage apparatus comprising:   a storage target for storing a charge pattern,   means for bombarding said storage target with an electron beam having a velocity capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas for storing information, and for bombarding said storage target with a beam of electrons for reading out stored information at a selected area of said target at which such beam is then directed, including means for pulsing said beam during read-out,   means for systematically scanning said beam of electrons, during read-out, over areas of the target where information is stored, and   means for directing a flood beam of electrons at such target for driving areas of such target towards one of two stable potentials by continued secondary emission from areas where information has been previously stored by secondary emission and by driving such target negative in areas where information has not been previously stored by secondary emission,   wherein such pulsation during read-out has a duration less than necessary to change a selected area from one stable potential to another, the flood beam of electrons driving such area back towards its stable potential in order to retain such stable potential of such area, and including means for causing said pulsation to be periodic and the period between successive pulses to be sufficient for said flood beam to retain the area being read out at its stored potential by driving such area entirely back to its normally stored potential whereby the sequence of pulsations does not drive such area from one stable potential to another. .Iaddend..Iadd.   
     
     
         9.  A charge image storage apparatus comprising: a storage target for storing a charge pattern,   means for bombarding said storage target with an electron beam having a velocity capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas for storing information, and for bombarding said storage target with a beam of electrons for reading out stored information at a selected area of said target at which such beam is then directed, including means for pulsing said beam during read-out,   means for systematically scanning said beam of electrons, during read-out, over areas of the target where information is stored,   means for directing a flood beam of electrons at such target for driving areas of such target towards one of two stable potentials by continued secondary emission from areas where information has been previously stored by secondary emission and by driving such target negative in areas where information has not been previously stored by secondary emission,   wherein such pulsation during read-out has a duration less than necessary to change a selected area from one stable potential to another, the flood beam of electrons driving such area back towards its stable potential in order to retain such stable potential of such area,   detection means coupled to said target for providing a read-out signal corresponding to said pulsations and indicative of information stored on the systematically scanned areas of said target, and   including a second charge image storage apparatus comprising a storage tube disposed at a location remote from said first mentioned charge image storage apparatus, and   communication means between the first mentioned charge image storage apparatus and the charge image storage apparatus at the remote location including means for synchronizing the systematic scan at both such locations, such communication means coupling the output from the detection means of the first mentioned charge image storage apparatus to the second charge image storage apparatus for storage at the latter location. .Iaddend..Iadd. 30. A charge image storage apparatus comprising:   a storage target for storing a charge pattern,   means for bombarding said storage target with an electron beam having a velocity capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas for storing information, and for bombarding said storage target with a beam of electrons for reading out stored information at a selected area of said target at which such beam is then directed, including means for pulsing said beam during read-out,   means for systematically scanning said beam of electrons, during read-out, over areas of the target where information is stored, and   means for directing a flood beam of electrons at such target for driving areas of such target towards one of two stable potentials by continued secondary emission from areas where information has been previously stored by secondary emission and by driving such target negative in areas where information has not been previously stored by secondary emission,   wherein such pulsation during read-out has a duration less than necessary to change a selected area from one stable potential to another, the flood beam of electrons driving such area back towards its stable potential in order to retain such stable potential of such area,   wherein the time duration, t, for a pulsation is less than the product of the voltage at the first crossover point in the secondary emission characteristic of the target and the capacitance of a target area read out, said product being divided by the sum of the reading beam current multiplied by (1 minus the secondary emission ratio for the reading beam), and the flood beam current multiplied by (1 minus the secondary emission ratio for the flood beam). .Iaddend. .Iadd. 31. A method of reading information from charge image storage apparatus including a dielectric storage target, a high velocity electron beam means directing a high velocity beam at said storage target, a low velocity flood gun means directed at said storage target for retaining information thereon, and means coupled to said target for providing a read-out signal, said method comprising:   directing a high velocity beam from said first electron gun at a particular area of said storage target for reading information from the same,   pulsing said electron beam from said first electron gun with a pulse having a duration less than necessary to change an area being read out from one stable potential to another such stable potential, repeating such pulse with a frequency such that the period between pulses is sufficient for said flood beam to retain such area at a stored potential value by driving such area back towards its stored potential,   scanning said electron beam in a regular pattern across the areas of said target storing information at the same time such beam is pulsed, and   deriving from said means coupled to said target, read-out pulsations corresponding to pulses applied to said first electron gun and indicative of the polarity of stored information,   wherein the duration of a pulse is less than the product of the voltage at the first crossover point in the secondary emission characteristic of said target and the capacitance of the area of said target being read out, said product being divided by the sum of the first beam current multiplied by (1 minus the secondary emission ratio for the beam from the first electron gun), and the flood beam current multiplied by (1 minus the secondary emission ratio for the flood beam) and wherein the period between pulses is greater than the product of the voltage at the first crossover in the secondary emission characteristic of the target and the capacitance at the area being read out, said product being divided by the flood beam current multiplied by (1 minus the secondary emission ratio for the flood beam). .Iaddend. .Iadd. 32. A charge image storage apparatus comprising:   a storage target for storing a charge pattern,   means for bombarding said storage target with an electron beam having a velocity capable of causing secondary emission from selected areas of said storage target upon which said beam is directed to change the voltage at such selected areas for storing information, and for bombarding said storage target with a beam of electrons for reading out stored information at a selected area of said target at which such beam is then directed, including means for pulsing said beam during read-out,   means for systematically scanning said beam of electrons, during read-out, over areas of the target where information is stored,   means for directing a flood beam of electrons at such target for driving areas of such target towards one of two stable potentials by continued secondary emission from areas where information has been previously stored by secondary emission and by driving such target negative in areas where information has not been previously stored by secondary emission,   wherein such pulsation during read-out has a duration less than necessary to change a selected area from one stable potential to another, the flood beam of electrons driving such area back towards its stable potential in order to retain such stable potential of such area,   detection means coupled to the charge image storage apparatus for providing a read-out signal corresponding to said pulsations and indicative of information stored on the systematically scanned areas of said target,   a cathode ray tube disposed at a location remote from said first mentioned charge image storage apparatus, and   communication means between the charge image storage apparatus and said cathode ray tube at said remote location including means for synchronizing the systematic scan at both such locations, said communication means coupling the output from the detection means of the charge image storage apparatus to the cathode ray tube at the latter location. .Iaddend..Iadd. 33. The apparatus according to claim 32 further including pulse stretching means for stretching the output of said detecting means. .Iaddend.