Image intensifier tube device

Abstract

An image intensifier tube device including a plurality of diode image intensifier tubes. Each tube comprises a sealed cylindrical envelope having its one end closed by an entry window carrying a photo-sensitive, electron emitting layer enclosed by a good electrically conductive rim. A resistive layer is deposited by vaporization between the circumference of the electron emitting layer and the good electrically conductive rim, which resistive layer is connected to a terminal of a voltage source having its other terminal connected to an anode and to focussing means of the tube such that in response to a sudden increase in the brightness of the image to be intensified a voltage drop is produced across the resistive layer, as a result of which the emitted electrons are de-focussed and/or deflected.

We claim: 
     
       1. An image intensifier tube device including one or more diode image intensifier tubes, comprising a sealed cylindrical envelope having its one end closed by an entry window on the inner surface of which a photosensitive, electron emitting layer is deposited which is in good electrical contact with, and enclosed by, a substantially circular, good electrically conductive rim, and having its other end closed by an exit window on which an anode in the form of a phosphor screen is deposited, means being provided for focussing a beam of electrons released from the photo-sensitive, electron emitting layer by incident radiation, said means comprising at least a cathode flange mounted around the substantially circular, good electrically conductive rim, the cathode flange being sealed .[.by fritting.]. to the entry window and being electrically connected to an electrically conductive, cylindrical member which constitutes part of the envelope, the device further comprising a source of voltage located outside the envelope, said voltage source having its positive terminal connected to the anode and supplying such voltages to the anode, the focussing means and the photosensitive, electron emitting layer, that an electric field is formed within the envelope which focusses the beam of electrons released from the photo-sensitive electron emitting layer onto the anode, characterized in that at least one diode image intensifier tube comprises a layer .[.deposited by vaporization.]. between the good electrically conducting, substantially circular rim and the assembly of the cylindrical member and the cathode flange, said layer having a high resistance and low capacitance so that, upon a sudden increase in the intensity of the radiation incident on the photo-sensitive, electron emitting layer takes place up to a level where there is a danger of anode burnout by the released beam of electrons, the increased emission current caused thereby sets up a voltage difference between the good electrically conducting, substantially circular rim and one of the focussing means, such that the electrons are de-focussed and/or deflected. 2. .[.An.]. .Iadd.The .Iaddend.image intensifier tube device according to claim 1, characterized in that said layer .Iadd.is .Iaddend.deposited by vaporization .Iadd.and .Iaddend.has a linear characteristic and a resistance greater than 1 MΩ and a capacitance less than 5 pF. 3. .[.An.]. .Iadd.The .Iaddend.image intensifier tube device according to claim 1, characterized in that said layer .Iadd.is .Iaddend.deposited by vaporization .Iadd.and .Iaddend.has a non-linear characteristic such that for an emission current below approximately 100 .[..[.m.]..]. .Badd.n.Baddend.A the resistance is below 1 MΩ and for an emission current above 100 .[..[.m.]..]. .Badd.n.Baddend.A the 
     
     
        resistance is above approximately 10 MΩ. .Badd. 4. In an image intensifier tube having an envelope containing an electron emitting cathode surface, focus means for establishing an electric field configured to accelerate and focus electrons emitted from said cathode and a phosphor anode surface for receiving the accelerated electrons, the improvement comprising in combination flash protection means for limiting burnout of the phosphor surface from sudden increases in current intensities, said flash protection means including resistance means exhibiting low capacitance disposed inside said envelope connected to produce a voltage change at said focus means in response to electron flow between said surfaces effective to reduce the impact of accelerated electrons reaching 
     
     
        said phosphor surface below burnout level. .Baddend. .Badd. 5. The improved image intensifier tube according to claim 4 wherein said image intensifier tube takes the form of a diode having anode and cathode 
     
     
        electrode structure. .Baddend..Badd. 6. The improved image intensifier tube according to claim 4 wherein said resistance element is interposed between said cathode surface and said focus means to influence electrons 
     
     
        at low velocity emitted by said cathode surface. .Baddend..Badd. 7. The improved image intensifier tube according to claim 4 wherein the focus means includes a cylindrical member forming part of the envelope between said emitting cathode surface and phosphor anode surface, and said resistance element being connected between said cathode surface and said 
     
     
        cylindrical member. .Baddend..Badd. 8. The improved image intensifier tube according to claim 7 wherein said emitting cathode surface has an electrically conductive annular ring thereabout, and said resistance element being a thin annular film connecting said electrically conductive 
     
     
        annular ring to said focus means. .Baddend..Badd. 9. The improved image intensifier tube according to claim 4 wherein said resistive element exhibits a non-linear characteristic manifesting increased resistance as a 
     
     
        function of increased current flow. .Baddend. .Badd. 10. The improved image intensifier tube according to claim 4 wherein said focus means includes two adjacent conductive cathode sections and said resistance element is connected to at least one of said sections. .Baddend..Badd. 
     
     
            The improved image intensifier tube according to claim 4 wherein the resistive element has a resistance greater than 1 MΩ and a capacitance less than 5 pF. .Baddend.