US2258436A - Phototube for translation of images - Google Patents

Description

Oct. 7, 1941. I vo ARDENNE 2,258,436

' PHO'IOTUBE FOR TRANSLATION OF IMAGES Filed June 1, 1935 7 INVENTOR.

771a n/"r'ea Iron drdenm ATTORNEY.

Patented on. 1, 941

rnoro'ruas roa'rnsnsurron or Manfred von Ardenne,

' to Radio Patents Guam-stun, New Yorh'N. 1.,

I a corporation of New ork Application June 1, is

' In Germany June sslseusim. m

BClaims. ((21.250-415) C h p The object of my present invention vision of an apparatus for amplifying the brightness of pictures characterized by the capacity to is the proproduce an electron emission the distribution'of which corresponds to thecharacter of the picture the brightness of which is to be amplified and by the capacity to make visible the electron 611118. sion on a fluorescent screen in the form of an image correspondnig to the original picture but having a greater brightness than the latter.

The fact that the quantity of light emanating from the fluorescent screen of an electron tube may be essentially larger than the quantity of light causing the emission of the photo-active cathode of the same tube will be understood from the following. 7

If for instance the light of a glow-lamp strikes a layer of caesium in high vacuum the current amounts to 40.10 Amp. per lumen (see Handbuch der Bildtelegraphie' und des Fernsehens," by Schrdter, 1932, page 182). In case of an accelerating voltage of 10 volt the efiect produced on the screen amounts to 4 watt per lumen. Supposing that the screen delivers the brightness of two candles (Hefner) for each watt of the eiTect produced by the electrons, the whole brightness per each lumen of the original radiation corresponds to 8 candles (Hefner); herefrom results that the total brightness of the light emanating from the screen corresponds to the value of 100 lumen. (See Lehrbuch der praktischen Physik, by F. Kohlrausch, th edition, page 414.) The amplification obtained is 100. The amplification is proportional to the voltage. The very high efliciency is caused thereby that the kinetic energy of the photo-electrons is enormously increased by the acceleration produced in the space between the photo-active layer and the fluorescent screen. While the velocity of the photo-electrons emitted by the photo-active layer amounts to a few volts the velocity at the screen is brought to a very high voltage (in the instance regarded to 10 volts). The high efflciency, as pointed out, essentially depends on the accelerating voltage; therefore the latter must be so high that in spite of the losses by the optical system or systems the efliciency will be more than 100% and an amplification is obtained.

The amplification can still be essentially increased by arranging two or more amplifying units in a cascade. The number of units, however, is limited; in case of too many units dis turbing deviations corresponding to the emission of individual photo-electrons in the first unit become visible (Schrot-Eilekt). The amplification by cascade is more advantageous than the amplification by only one unit as one can use lower voltages.

erence numerals denote like parts in the diiferent views thereof:

Fig. 1 is a schematical plan view an embodiioment of my invention comprising one amplifying nit,

Fig. 2 is a schematical plan view of another embodiment similar to that shown in Fig. 1,

Fig. 3 is a schematical plan view of an embodiment of my invention comprising two amplifying units in cascade, p

Fig. 4 is a schematical plan view 'of another embodiment. similar to that shown in Fig. 3.

According to Fig. 1 the apparatus comprises only one amplifying tube I, the cathode of which is formed by a photo-electric or photo-active layer 2 applied to one of the parallel end walls of the tube'while the opposite end of the tube forms the fluorescent screen 3. Between the cathode and the screen an electrostatic accelerating lens 4 with a relatively large opening and a cylindrical electron lens 5 are provided. Near the rear end of the tube i a parabolic mirror B is arranged in such a position that the picture to be transmitted is reflected upon the photo-active layer 2. The tube I is surrounded by a screen I serving as light protector and as means practically neutralizing any divergence caused by the high brightness of the image on the screen 3. In accordance with the direction of radiation a vertical image of the picture appears on the screen, whereby the sharpness of the image is obtained if necessary by regulating the electric potential of the electrode 4. The operating potentials for the electrodes 4 and 5 are supplied by a suitable high tension source indicated by the and signs and shunted by a potentiometer 8 with suitable tap connections as shown in the drawing.

The a paratus schematically shown in Fig. 2

differs from that shown in Fig. l essentially thereby, that the photo-active layer 2 as well as the fluorescent screen 3 are arranged on a suitable base 9 and I0, respectively, mounted in inclined position with regard to the axis of the tube I. Due to the inclination of the layer 2 more simple and smaller optical means such as a lens system shown at H for the optical transmission of the picture may be used. The inclination of the screen 3 enables the use of a screen on which the image becomes visible on the inner side, whereby the eiliciency of amplification is improved. By simultaneously inclining both the photo-active layer 2 and the screen 8 a. sharp image of the whole surface of the layer is obtained on the screen. Only a small error occurs which, however, may be optically corrected if such is desired. Both inclinations must be held in a definite mutual relationship in order to obtain the desired sharpness at all points of the screen surface. This relationship depends on the resulting relation between the size of the image on the screen and that on the photo-active layer and further depends on an average index of refraction of the mediums on both sides of the electron lens. In case of Fig. 2 the photoactive layer 2 which is arranged on the side where the velocity of the electrons is small (great index of refraction), is less inclined towards the axis of the tube I than the fluorescent screen 3, which is arranged on the side where the velocity of the electrons is high (small index of refraction).

Fig. 3 illustrates an apparatus which comprises two amplifying units arranged in cascade. The second unit which is substantially identical to the first unit comprising the tube I3, inclined plate I4 coated with light sensitive material I5, inclined base I6 coated with fluorescent material I'I, first or acceleration electrode I9 and electronic lens 20. Item I8 represents an optical lens or lens system for projecting the fluorescent picture from the screen 3, II) of the first amplifier I upon the light sensitive input screen I4, I of the second amplifier I3. As the units are wholly separated from each other, a common source of voltage with associated potentiometer 8 can be used for both units as shown in the drawing. In cascade arrangements it is advisable to provide that the product of the electron-optic enlargement and of the enlargement obtained by the optical coupling between the screen of one unit and the photo-active layer of the following unit, is I. Of course one is enabled to gradually provide enlargements or reductions. The photoactive layer 2 of the first unit I is preferably so prepared that the maximum of its sensitiveness corresponds to the maximum of the radiation to be amplified. The screen of the first unit as well as the photo-active layer of further units consist of such material that a total efficiency as high as possible is obtained. For instance screens delivering blue light and corresponding layers will be better than screens and layers otherwise pre ferred for light of longer waves. The screen of the last unit is so manufactured or prepared that the maximum of its radiation corresponds to the maximum of sensitiveness of the human eye.

Fig. 4 shows another arrangement of two units of the type shown in Fig. 1 in cascade wherein the fluorescent surface 3 of the first unit is disposed directly opposite the photoelectric surface I5 applied to the transparent wall of the second unit with a transparent sheet of insulation 2I separating the two tubes which, however, will hardly satisfy higher requirements with regard to the sharpness of the image produced, and in which very high accelerating voltages cannot be used. The photo-active layers and the fluorescent screens are very thin. The use of a common source of voltage for both units is enabled by providing a transparent thin insulating layer 2| between the fluorescent screen of the first unit and the photo-active layer of the second unit.

What I claim is:

1. A photoelectric tube including a cathode and an anode having faces presented, toward each other, the face of said cathode being coated with a substance capable of emitting electrons in proportion to the intensity of light rays striking the same, the face of said anode being coated with a substance adapted to give off lightrays in proportion to electrons striking said substance, said cathode and said anode being spaced apart sufficiently so that light rays may be projected upon the coated face of said cathode to form a distinct image throughout an extended area upon said cathode face and so that the image upon said anode may be viewed by an observer, electron lens means between said cathode and anode for accelerating and focusing the electron image upon said cathode face onto said anode coating,

and means for projecting an optical image upon the coated face of said cathode.

2. A photoelectric tube including a cathode and an anode having faces presented toward each other, the face of said cathode being coated with a substance capable of emitting electrons in proportion to the intensity of light rays striking the same, the face of said anode being coated with a substance adapted to give off light rays in proportion to electrons striking said substance, leads for applying a difference of potential to said cathode and said anode, and lenses positioned to cooperate with said faces to provide passages for light rays to said cathode and from said anode.

3. A photoelectric tube having a cathode coated on one side thereof with a substance which under the effect of light rays emits electrons and an anode having a coating presented to the coated side of said cathode, said coating on said anode being capable of emitting light rays proportional to electrons hitting said coating, said cathode and said anode being spaced apart sufficiently so that light rays may be projected upon the coated face of said cathode to form a distinct image throughout an extended area upon said cathode face and so that the image upon said anode may be viewed by an observer, electron lens means for accelerating and focusing the electron image upon said cathode face onto said anode coating, and optical lens means for focusing an image upon the coated side of said cathode.

4. A photoelectric tube including a cathode and an anode having faces presented toward each other, the face of said cathode being coated with a substance capable of emitting electrons in proportion to the intensity of light rays striking the same, the face of said anode being coated with a substance adapted to give off light rays in proportion to electrons striking said substance, and leads for applying a difference of potential to said cathode and said anode, said cathode and said anode being spaced apart sufilciently so that light rays may be projected upon the coated face of said cathode to form a distinct image throughout and extended area of said cathode face and so that the image upon the coating of said anode may be viewed by an observer.

5. A photoelectric tube comprising a light sensitive cathode having an extended surface, a luminescent screen coated with a material capable of emitting light rays by electrons striking the same, said cathode and screen being mounted at an angle to the axis of said tube, and electron lens means mounted between said cathode and screen for accelerating and focusing the electron an extended cathode coated with a substance capable of emitting electrons in proportion to the intensity of light rays striking said substance, a luminescent screen coated with a substance capable of emitting light rays in proportion to electrons striking the same, and electron lens means for focusing an electron image on the cathode of each unit onto the screen of the same unit, means for projecting an image comprised of rays within a predetermined spectral range upon the cathode oi. the first unit, the substance coating the cathode of said first unit being responsive substantially to rays of said predetermined spectral range, means for projecting the image produced by the screen of each unit onto the cathode oi MANFRED von ARDENNE.

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