USRE23802E

USRE23802E - Photocathode

Info

Publication number: USRE23802E
Authority: US
Priority date: 1948-11-05
Publication date: 1954-03-16
Also published as: US2603757A

Description

PHOTOCATHODEI E. E. SHELDON Original Filed Nov. 5, 1948 March 16, 1954 Reissued Mar. 16, 1954 assez rno'rocsrnons Edward Emanuel Sheldon. New York, N.Y. origins: No. 2,603,751, dates .my 15, 1952. serial November 5, 1948. Application for reissue July 13, 1953, Serial .Ultima (Cl. 313-101) Matter enclosed In heavy brackets I: j appears in the mantenuti :umanamente reissue specication; matter printed in italics indicates the additions made by reissue.

This invention relates to novel type of photocathodes for eiiicient picking up oi signals or complete images produced by dinerent types of invisible radiations and to novel type of electrodes for intensincation oi' said signals or images produced by invisible radiations.

The purpose o! my invention is to provide photocathodes which will emciently respond to invisible iight radiation. as well as to atomic particles radiation.

Another purpose of this invention is to provide photocathode's i'or conversion oi signals or images oi one type oi radiation into another type oi' radiation.

Another 'purpose of this invention is tc preserve ndelity ,oi reconverted signals or images in relation to the original signals or images.

Another purpose oi this invention is to provide a universal electrode for intensication oi' signals or images. which ls responsive to all types or radiation.

The present photocathodes are made oi photoemissive, photo-conductive or of photo-voltaic layer on a suitable supporting base. These photocathodes responded well to visible light. They are. however. very insensitive to intra-red radiation oi' wave-length longer than one micron andon the other end of the spectrum to rays oi' wavelength shorter than 2000 A. These photocathodes are also completely insensitive to electron or other atomic particles radiation. Limitations oi the present photocathodes were eliminatedin my invention by the use oi composite photocathodes comprising in combination light reiiecting layer transparent to exciting radiation, fluorescent layer. light transparent layer and photo-sensitive layer disposed in a suitable vacuum tube. This novel photocathode may be used in every Bienal or image reproducing System. as we ll as in every signal or image transmitting system such as. phototubes, electronmultiplier tubes. in imageA converters, in image ampliilers. and in television pick-up tubes. By using this novel photocathode the invisible exciting radiation is converted in the iiuorescent layer oi' said composite photocathode into iluorescent light of wavelength to which the photosensitive layer of said photocathode is most sensitive. The fluorescent light is exciting said photo-sensitive layer directly and by reiiection from said reflecting layer, whereby any loss of fluorescent light is prevented increasing markedly the efiiciency o! Ythis novel photocathode. In this way radiation which would be too weak to excite the conventional photocathode may now produce photo-electric eilect. The sensitivity ot the novel photocathode is further increased by elimination oi' the optical system forprjection oi' the signals or images on the photocathode. In the conventional photocathode the signals or images after their conversion into type oi radiation to which said photocathode is sensitive. have to be projected thereon by means ot optical system. The use oi' the optical system causes loss of of radiation because of absorption. Elimination of the optical system would obviously result in complete deterioration oi' the sharpness oi' projected image on the conventional photocathode. oi illumination is removed without impairing sharpness oi the image, because of close apposition ot iiuorescent and photo-sensitive layers. This is equivalent to 20-30 fold gain in sensitivity oi' the photocathode.

Another important feature oi' the novel photocathode is the presence oi transparent .layer be tween the iiuorescent and photosemitive layers. This separating layer being extremely thin. oi' a few microns only, does not cause any deterioration of sharpness and at the same time prevents chemical interaction ot uorescent and photosensitive layers which isf the cause of serious complications such as spurious signals. hl. etc.

The photo-electric signals or images produced by the novel photocathodecan be further intensitled by the use of similar composite electrode comprising light reflecting layer, electron iluorescent layer. light transparent separating layer and photo-electric layer, disposed in a single' or plural successive stages in the vacuum tube in cooperative relationship with said photocathode..

The invention will be better understood when takeninconnection with the drawings.

In the drawings:

Fig. 1` represents composite photocathode responsive to electron radiation.

Fig. 2 represents composte photocathcde sensitive infra-red radiation.

Fig. 3 represents composite photocathode re sponslve to ultra-violet radiation.

Fig. 4 represents composite photocathode responsive to X-rays and atomic particles radiation 1 Fig. 5 represents composite photocathode sensitive to X-ray and gamma radiation.

Fig. 6 represents an alternative form ot photocathode sensitive infra-red radiation Fig. '7 represents an alternative form oi com- In my invention. this cause o! the lo` 3 posite photocathode sensitive to X-ray and atomic particles radiation Fig. 8 represents composite photocathode responsive to infra-red having photo-sensitive layer of photo-voltaic type.

Fig. `9 represents novel composite electrode.

Fig. 10 represents composite electrodes arranged in successive stages for image amplification.

Fig. il represents cascade i'orm o! composite electrode.

Fig. l represents composite photocathode l hav-` ing light reecting layer 2, fluorescent layer l, extremely thin light transparent separating layer I. and photo-sensitive layer e. g. ot photo-emissive type 5. This photocathode is the moet suitable for atomic particles radiation such as electrons 6 and for invisible electrode-magnetic radiation o! wave-length shorter than 2000 A. The electron radiation passes through light reflecting layer 2 ot aluminum. is .striking Vthe fluorescent layer I ofZnSAg or i' B'aBOi and is converted therein into fluorescent light which is exciting directly and by reflection from the reilecting layer 2 the photo-emissive layer 6 oi caesium. lithium or potassium on antimony or bismuth. The transparent separating layer l may be ofmica, silicon.

or of a suitable plastic. The fluorescent materialx auch as 'ZnSAg or Beso; have the property of emitting also ultra-violet luminescence besides the visible luminescence. ZnFlz is transparent to ultra-violet radiation. Silicon and ZnFla crematerials which can be evaporated. This composite photocathode is characterized by marked sensitivity. It is 200 times more sensitive than the conventional photocathode to irradiation by atomic particles or light of wave length shorter than 2000 A. At the same time because of close proximity of fluorescent and photo-emissive layers, the conversion o! signals and images is possible with preservation of the sharpness, in spite oi the elimination oi optical system for pro- Jection o! said signals or images on said photocathode.

Fig. 2 represents composite photocathode i0 suitable for infra-red radiation. The iluorescent layer 'I may be oi' alkaline earth sulphides or selenides activated by cerium, samarium or by CuPb. This nuotescent layer converts the infrared signals I0a into iiuorescence of 60G-,1000 miliimicrons wave length. which is exciting the photoemissive layer l of CsOAg or of CsO and is producing pbotoeleotron emission. The transparent separating layer I may be o! mica, silicon. or oi a suitable plastic. This composite photocathode is responsive to intra-red signals or images which would not be able to activate any known at present photocathode.

Fig. a illustrates composite photocathcde I I sensitive to ultra-violet radiation Ila. The iluorescent layer l! is of calcium phosphate with activators. or or calcium silicate or barium silicate with activators. The light transparent separating layer Il is of mica. silicon or a suitable plastic. The photoelectric layer il is of caesium or potassium on antimony. The iluorescent layer I2 when excited with short U.-V. radiation Ila converts it into ultra-violet fluorescence ot'3,0003,800 A. wave-length, which is able to excite the photoelectric layer il. The advantage or this novel photocathode is, besides its sensitivity, the tact that it is responsive to very short ultra-violet radiation. to which none of the present photocathodeslssensitive.

4 is sensitive to X-rays and atomic particles radiation. photocathode comprises light reflecting layer Il such as, of aluminum. iiuorescent layer i1 of ZnSCdSAg, BaBOg. or o! tungstate. The separating layer Il is light transparent and may be oi mica. silicon, Znllz or of suitable plastic. 'Ihe photo-electric layer il is of photo-conductive type and may be of selenium. ZnB. CuS. Phs or of thallium sulphide. The signal plate 2011s ot conductive metal. The invisible X-ray radiation Il is converted into uorescent light in the layer II. The iluorescent iight irradiating the photo-conductive layer I9 changes its resistance producing thereby electrical signals modulated by the pattern oi' said invisible X-ray image. The electrical signals now through the signal plate 2l to appropriate receivers.

Fig. 5 illustrates an alternative form ot the photocathode shown in the Figure 4. In this embodiment of the invention the photocathode lia. comprises liglt r'eecting layer I6, iiuorescent layer I'I. light transparent layer It. photo-conductive layer Il, another iluorescent layer Ila and signal plate 2l. This type o! photocathode is very sensitive to X-rays and gamma rays. The photo-conductive layer l! is in this form o! invention irradiated by the uorescent light trom both sides, from layer II and Ila, producing double photo-conductive eil'ect.

Ilig.` 6 illustrates variety of photo-conductive photocathode 2l suitable for infra-red radiation 28. The iluorescent layer Il is of alkaline earth sulphides or selenides activated by' cerium, samarium or europium. The separating light transparent layer It is ot mica. silicon or ot suitable plastic. The photo-conductive layer 2li is of selenium. Z118, CuB. PbB or oi thallium sulphide. The signal plate of conducting metal 21 serves to transmit electrical signals modulated by intra-red image to appropriate receivers.

The photo-conductive composite photocethode may be also made sensitive to ultra-violet radiation by making the fluorescent layer 24 ot said photocathode 2l of ZnBAg. of BaSOi or of calcium or barium silicates with proper activators.

Fig. illustrates photo-voltaic type of composite photocathode IB having light reilective layer 29, for example. o! aluminum, iluorescent layer of ZnB, CdSAg, germanates or of ZnSCu I0, light transparent layer of mica, silicon or of suitable plastic Il. photo-voltaic layer ot CuzO on Cu 82 and signal plate I! ci conductive metal. The in- `visiblegX-rey radiation M is converted in the fluorescent layer Il in the nuorescent iight which is exciting the photo-voltaic layer Il directly and by reflection from the reiiecting layer 2l causing diilerences in potential over the surface of said photo-voltaic layer. dlfierenceg in pgtential have the pattern of the original invisible X-ray image. They are conducted in the form of electrical signals by the signal plate u to appropriete receivers.

Fig. 8 shows an alternative form o! photovoltaic photocathode which is sensitive to radiation o! long wavelength such as infra-red Ila. This composite photocathode Il consists ot iluorescent layer 3i of alkaline earth sulphides or selenides activated by cerium. samarium or europium, of iight transparent layer 36 ci mica., silicon or oi' suitable plastic; of photo-voltaic layer 3l of CuaO on Cu and of metallic signal plate 3.8. The intra-red radiation is converted by the nuorescent layer of said photocathode into fluorescent light which exciting said photo- Fig. 4 shows composite photooatlwd l! which 75 voltaic layer causes dinerences in potential over iis surface. These dillel'ne in potential have the pattern or original infra-red image. They are converted into electrical signals and are conducted by the signal plate to receivers.

Fig. 9 illustrates composite electrode lil in vacnum tulle l for lntenslncatlon of signals or images. This novel electrode can be used for signais or images oi' all types oi' radiation. It has light reflecting layer 4l, which is ltransparent to electrons, layer iluorescent under electron irradiation lig-light transparent layer 3 and photoemissivel'layer 44. In particular the light reflecting layer Il may be of aluminum, the electron uoresceht layer l2 of ZnSAg or of BaSG4, the light transparent separating layer 43 which may be of materials described above for the light #emparent separating llayer 4, the photoemiaeioe layer 44 may be of caesium, potassium or lithium on antimony or bismuth. As images ot all types of invisible radiation may be converted by a suitable compos-ite photo-emissive phoioeathode, as described above. into photoelectron image. the novel electrode which is electron-sensitive may serve for intensiilcation o! signals and images whether they are produced by U.V.. I-R, gamma rays or by atomic particlesa.,

In the Flglire 9, we see intensication oi' electroiig image by said composite electrode I5. The elec- `tron beam Il carrying the invisible electron image, such as e. g. radar image is focused on the composite electrode 45.' The electron image passesthrough the `light reilecting layer 4|. is converted by the ilucrescent layer l2 into nuorescent image and said fluorescent image is exciting photo-emisslve layer M, whereby intensifledphoto-electron image navi-ng the pattern of the original radar image is obtained and may be now reconverted into .visible image. if so desired This process of intensincation may be repeated a few times using said composite electrodes in a few stages. whereby additional intensincation is obtained. In ease el radar images the fluorescent layer in the composite electrode 46 should be in some instances oi' a long persistence. in. order to avoid `the flicker. Such persistent fluorescent phosphor may be oislngle layer type suchv as e. g. Zn(Mg)Fa:Mn or other iluorides. ZnBCu(Agl; CsaPeOrxDy or Z'nBCdBmmCu. Sometimes it is more advantageous to use cascade type or fluorescent screen consisting of two or more layers, as illustrated in theFigm-e 1l. In this .form of invention the composite electrode "a has the fluorescent layer a comprising two layers 12b and llc such .as e. s. ZnBlAg) on ZnSiCdkCu or A120; on ZnSzfAg). Obviously there are many combinations of cascade long persistent fluorescent screens which can be used in this invention. The remaining parts of the composite electrode a such as light reflecting layer Ila. light transparent separating layer a and photo-emlssive layer a are as described above.

The application of the composite electrode 4l for visible light image amplication is shown in the Figure 10. The visible light image Il pro- Jected by the optical system Il causes photoemissive etl'ect in the photocathode 4l disposed in the vacuum tube Il. The photo-electrons released irom the photocathode 48 and having pattern of said light image strike the composite electrode 45, and produce intcnsiiied iluorescent image in the iluorescent layer I2 oi said composite electrode. The lntenslned fluorescent image directly and by reilection from the light relayer 4I, producing intensined secondary photoelectron image. This intensified secondary photoeleetron image having the pattern of the Voriginal light image may be projected on the `nest composite electrode il having llsht reilecting layer il. electron-uorescent layer u. light transparent separating layer ll and photo-emissive layer 5G whereby additional intensiilcation is achieved. This process may be repeated 'in a -ftew stages resulting in marked intensification of the original light image. lbefore reconverting said intensined secondary photo-electron image-into ilnal visible image for inspection or recording. This syste-m ot light image amplification was never accomplished successfully before as in previous systems the absence of the lightreilccting layer 4| in the composite electrode caused back-scattering o! the fluorescent light Afrom the fluorescent layer 42 to the phctofc'athode 4I, destroying thereby completely the image.

It is obvious that thenovel composite photocathode and composite electrode may be' Aused in every signal or imago reproducing or transmitting system. InV particular they willbeused in photo-tubes. electron multipliers. image oonverters, image empl-mer tubes as well as television pick-up tubes. whenever the presently known photo-cathodes are not responsive or not sensitive enough to the depicting radiation.` A

Although the preferred embodiments of theinvention have been described it will laborious to those skilled in the art that various changes and modiilcations may be made without departing from the true` spirit and scope ol this invento Vprotect by Letters Patent of the United States: Y l. In a vacuum tube. a composite screen com-.- prlsing a luminescent layer deposited on a wall of said tube. a light transparent separating layer in contact with said luminescent layer, said light transparent layer having a thickness oi' the order ot microns, and a photosensitlve layer in contact with said light transparent layer.

2. In a vacuum tube.- as delinea in claim` 1 wherein said photosensitlve layer is photoemissive.

claim l.

-' tion.

What I claim and Want 3. In a vacuum tube. as dened in wherein said luminescent layer comprises a plurality or layers of different phosphor-s.

4. In a vacuum tube. a composite screen comprising a luminescent layer deposited on a wall of said tube, va light transparent separating layer of the order of microns ln contact with said luminescent layer, andva Photoconductive layer in contact with said separating layer. 4

5. In a tube, a composite screen comprising a luminescent layer, alight `transparent separatino layer in contact with said luminescent layer, said light transparent separating layer having a thickness of the order of microns, and a photo.- electrie layer in contact with said light transparent layer.

6. In a tube as defined in claim 5, wherein said Photoelectric layer is photoemtssive.

7. In a tube as dened in claim 5, wherein said luminescent layer comprises a plurality of layers of allier-ent phosphore.

8. In a tube, a composite screen comprising a luminescent layer. a light transparent separating layer of a thickness of the order of microns and in contact with said luminescent laver, and a photoconductive layer in contact with said separating layer.

9. In a tube, a composite screen comprising ilecting layer Il is exciting the photo-emissive luminescent means, light transparent separating -ent means and the sapos means in contact with said luminescent means and also ,transparent to ultra-violet radiation` emitted bg said luminescent means, said lights transparent means having a thickness of that` order of microns, and a. photoelectric lager in contact with said transparent separating means 10. In a vacuum tube, a composite screen coms prising in the following order: a luminescent lager receiving an image for-ming radiation, cg light transparent separating lager also transpar entf'to ultra-violet radiation emitted bg said? luminescent layer, in contact with said luminesq cent layer and of a thickness of the order of microns, and a photoemissioe Alager in contact with said light transparent lager.

11. In a tube, a composite screen comprising in the following order: luminescent means re-'s ceiving an image forming radiation, light trans-` parent separating means of evaporabie materia 1 and in contact with said luminescent means, sai light transparent means having a thickness of the order of microns. and photoelectric means` receiving light from said luminescent mean through said light transparent separating mea and in contact with said light transparent pieanss` 2:,

12. In a vacuum tube, a composite screen com prising in the following order: a lumines lager receiving an image forming radiation, light transparent separating layer of euaporable material in contact with said luminescent layer and of a thickness of the order of microns, 'and a photoemissive lager in contact with said light transparent lager.

13. In a tube, a composite screen comprising luminescent means, light transparent separating means in contact with said luminescent means,` said light transparent means having a thickness of the order of microns, and a photoelectric layer having one surface in contact with said light-1 transparent means and the other surface ex, posed,

14.V In a tube, a composite screen comprising luminescent means, light transparent separating means in contact with said luminescent means and of eoaporable material, said light transpar-f ent means having a thickness not exceeding a few microns. and a photoelectric lager having, one surface in contact with said light transpar-l other surface exposed.

15. In a tube. a composite screen comprising in the following order: luminescent means re-v` ceiving image forming radiation, light transpar ent separating means of eoaporable material ir contact with said luminescent means and of a thickness of the order of microns, and photo-fw 5- electric moans m contact with said nani trans-" parent means and comprising an alkali metal combined with an element of the group including@J antimong or bismuth. ,f

16. In a tube, a composite screen comprising 60 X -raysi luminescent,` :means supporting means transparent to Xirags, lumi. nascent means said X-rags, light transparent separatinqemeans in contact with said luminescent means and of a thickness of the order of mignons, and photoelectric means hauing one in contact with said transparent separating .ns and the other surface exposed.

17. In a vacuum tube; a composite screen comprising in the following order: supporting means transparentV to Xssaps, luminescent means receioing said X-razls, iighttransparent separating means of eoaporaoie material in contact with said luminescent means and o! a thickness of the order of miercns, and a photoemissive lager in contact with said'tsamarent separating means.

18. In a tube, a composite screen comprising in the following onder.l supporting means transparent to X-rapphlminescent means receiving said X-rags, light transparent separating means of eoaporable material in contact with said luminescent means and "of a thickness of the order of microns, anhaphotoaonductive lager in contact with said tmsparent means.

19. A tube comprising a composite screen having in the ollowingsfsorder: supporting means transparent to X-rags, luminescent means receioing said X-rags, isg'lt transparent separating means of eoaporahle aterial in contact with said luminescent means and of a thickness of the order of microns. and a pIwtoGlectric layer having one surface in contact with said light transparent means and the other surface exposed.

20. In a tube, a composite screen comprising in combination supporing means transparent to receiving said X- rags, light tran `t separating means also transparent to altrasiiolet radiation emitted bg said luminescent in contact with said luminescent means-fan of the thickness of the order of microns, and photoelectric lager having one surface ,in contact with said transparent separating mms and the other surface exposed.

Ewsnp :MANUEL sHEmoN.

References qitedin the 111e of this patent ortls 9171853191 paient UNITED STATES PATENTS Nambe:79 Nxlxlx Date 2,198. 4 Apr. 23, 1940 2,200,853 Il-Jggsexxg'et al. May 14, 1940 2.233.296 Law .i Mer. 4, 1941 2,258, 36 Yonxdenne Oct. 7, 1941 2,259,372 isle;l Oct. 14, 1941 2,297,498 ann et al. Sept. 29. 1942 2,435,435 Fonda. Feb. 3, 1948 2.452.529 Laterina oct. 26. 194s 2.473.220 .x June 14, 1949 2,476,019 July 19. 1949 Certificate of Correction Reissue No. 23,802 March 16, 1954 Edward Emanuel Sheldon It, is hereby certified the; error appears in the printed specification of the above numbered patent requiring eorrecion as follows:

Column 3, line 18, for electrodemagnetic read electro-magnetic oolumn 5, line 11, for 3" read i3 sind that the said Letters Patent should be read as Corrected above so that the same may conform to the record of the :use in the Patent Office.

Signed and sealed this 25th day of May, A. D. 1954.

ARTHUR Wn CROCKER,

Assistant Commissioner of Patente.