US2433724A

US2433724A - Phototube multiplier

Info

Publication number: US2433724A
Application number: US537953A
Authority: US
Inventors: Lozure G Wolfgang
Original assignee: Farnsworth Research Corp
Current assignee: Farnsworth Research Corp
Priority date: 1944-05-29
Filing date: 1944-05-29
Publication date: 1947-12-30
Anticipated expiration: 1964-12-30

Description

Dec. 30, 1947. 1.. G.

PHOTOTUBE MULTIPLIER WOLFGANG 4 Filed May 29, 1944 FIG.2

F IG.3

I INVENTOR} LOZURE G. .WOLFGANG ATTORNEY Patented Dec. 30, 1947 PHOTOTUBE MULTIPLIER Lozure G. Wolfgang, Blufiton, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application May 29, 1944, Serial No. 537,953

This invention relates to electron multipliers and particularly to multipliers suitable for use in conjunction with phototubes.

"It is customary to employ phototubes for the purpose of translating light energy into electrical energy. The translating elements which have been used are incapable of developing electrical effects of any substantial magnitude in response to light incident upon the'translating elements. It, therefore, is necessary to employ in conjunction with the phototube, a means for amplifying or increasing the magnitude of the generated electrical effects inorder that they may be utilized. One convenient device for effecting such an amplification is an electron multiplier. In cases where the photosensitive element of the device has a relatively small electron emissive area, the electron multiplier may be located at a point adjacent one of the peripheral edges of the photosensitive element. Such devices have been found to give completely satisfactory results.

' However, as is well known in the art, the effectivene'ss of an electron multiplier is a function of the distance by which it is removed from the primary source of electron emission and the electron accelerating voltage impressed between the multiplier and the emission source. This characteri'stic, therefore, places certain limitations upon" the conventional arrangement ofan electron multiplier with respect to the electron emit-- ting cathode of a phototube. It generally is deexceed certain predetermined magnitudes. Acc'ordin'gly, for any given accelerating voltage the distance between the emission source and the multiplier for satisfactory effectiveness is limited.

The're are many instances where it is desirable that the phototube be provided with a cathode of considerable surface area. Consequently, there is a substantial portion of the cathode area which is so remote from an electron multiplier of the prior art type referred to that it is impossible to utilize the emission from these remote portions by means of accelerating voltages of reasonable magnitude. In thismanner the purpose of such a phototube multiplier is defeated, at least in part;

'It is an object of the present invention, therefore, to provide a phototube multiplier in which substantially all of the electron emission from a photosensitive cathode of considerable area is utilized' for multiplication without the use of electron accelerating voltages in excess of reasonable magnitudes.

In accordance with the instant invention there is provided a phototube multiplier comprising a photosensitive cathode having a centrally disposed aperture, There falsois provided a secondr 919031011 e i sive multiplier electrode having a portion disposed'in' the space contiguous to the 11 Claims. (Cl. 250-475) I so that it is in communication with the multiplier electrode through the cathode aperture. 7

' Fora better understanding of the invention, to gether with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope willbe pointed out in the appended claims.

In the drawing I Fig. 1 is a longitudinal sectional view of a phototube multiplier embodying the invention in o'neform; 1 1

Fig.2 is a transverse sectional view of the phototube multiplier taken on the line 2--2 of Fig. 31s a longitudinalsectional view of a phototube multiplier embodying the presentinvention in an alternative form; and,

Fig. .4 isa-longitudinal sectional view of a phototube multiplier embodying the presentinvention in still another form. 1 Having reference now particularly to Figs. 1 and 2 of the drawing, the illustrated embodiment of the invention is mounted within an evacuated e ope l l. Adjacent one end of the envelope there is provided a substantially fiat photosensitive cathode l2. Theelectron emissive surface of this cathode faces the adjacent end wall of the tube envelope which is formed of optically plane transparent material, such as glass. The cathode is provided with a centrally disposed circular aperture IS. A screen or wire mesh I4 is supported, in spaced relation to the photosensitive surface of the cathode I2 in a suitable manner such as by a flange l5 formed on the cathode.

An annular first stage multiplier electrode [6, which is provided with an exterior concave secondary electron emissive surface, is mountedin such a manner that a portion thereof extends through the cathode aperture l3 well into the space contiguous to the photosensitive surface of the cathode. The remaining portion of the electrode 15 extends into the space contiguous to the opposite surface of the cathode. In this embodiment of the invention the electrode l6 hasthe general surface configuration ,of an hour-glass...

There also is attached'to the upper edge of the electrode 16 a screen or grid I! which has a generally cylindrical form so that itsubstantially aperture l3. The screen ll iselectrically connectedto the electrode l6 and is insulated electriand the cathode l 2 may be secured by spacing" the screen from the edges of the cathode aperture. The electrode l6 and its associated screen ll may be insulated from the cathode screen F4 by means of a plurality of beads such as l ymade of glass or other suitable insulating material; In

this manner the inner portions of the cathode screen 14 may be attached tothe'insulatirig' beads I8 and thereby secure suitable support The third and fifth multiplier stages comprise electrodes I9 and 2| having the same general shape as the first stage electrode 16. The electrodes I6, l9 and 2| are disposed axially with respect to the cathode aperture l3 and perpendiciilarly to the plane of the cathode l2.

The second, fourth and sixth multiplier stages comprise

electrodes

22, 23 and 24. Each of these electrodes is annular and is provided with an interior ofi-cavescconuary electron emissive' sur face. v, These electrodesare disposed coaxially wit the series cf'extenor concave surfaced elec tr The

electrodes

22 and 23 are arranged to surround a portion of the space contiguous to are adjacent surfaces of the successive exterior concave surfaced electrodes l6 and I9. Similarly, the electrode 23 surrounds the space contiguous to the adjacent surfa es of'theelectrodes I9 and 2t. The electrode 24 surrounds the space con tiguous to the other end portion of the electrode 2i and also the" space contiguous to an electron collecting electrode 25. This latter electrode is provided with a substantially fiat surface and is mounted coaxially with the multiplier electrodes with its collecting surface parallel to the oath, ode l2.

The electrodes l9, 2|, 2:, 23 and .24 are each provided with a cylindrical screen such as 26, 21, 28, 29 and 3|, respectively. Each of the screens is electrically connected to its associated multiplier electrode arid is interposed between the respective electrodes and the immediately preceding electrode.

Electrical connections tothe cathode and to the multiplier electrodes are made through the press portion of the tube envelope 1 l to a conventional source of energy in' a well known manner (not shown). If desired, the conductors within the tube envelope may be made of sufficiently heavy gage wire to serve also as the mechanical supports for the associated electrodes in a manner well known in the art.

Having reference now to the operation of the form' of the invention illustrated in Figs. 1 and 2, before considering the other modifications of the invention, it is assumed that light coming from above as viewed in the drawingimpinges upon the photosensitive surface of the cathode l2. Electronsthus are emittedfrom the upper surface of the cathode at relatively low velocity. In accor-dance with well known practice the first stage multiplier electrode l6 has impressed thereon a potential .of the order of a hundred volts positive with respect to the cathode [2. By reason of the electrical connection of the screen I 1 to the multiplier electrode Hi, there is created in the vicinity of screen an electrical field of a strength commensurate with the potential impressed upon the electrodelfi. Inasmuch as the screen J1; and a substantial portion of the electrode i5 is located in the space contiguous to the emissive surface of the cathode I2, electrons from allpoints of ncestuous are readily accelerated toward the electrode I 6. Thus, the electron acceleratin effectiveness of the first multiplier electrode isso materially increased that a cathode of much greater surface area may be used than in-devices of this general character known to the prior art,- Where the multiplier is located adjacent the peripheral edge of the cathode.

The impingement of the photoelectrons upom the secondary emissive surfaces of the electrode lfi'is efiect'e'd with sufiicient velocity to cause the emission by this electrode of increased numbers of"secondary electrons. These secondary elec-- trons immediately come under the influence of the field created in the vicinity of the screen 28 associated with the second stage multiplier electrode 22 and are caused to strike the secondary emissive' surface of this electrode at sufilcient velocity to effect the emission of multiplied. numbers of secondary electrons.

The operation of the multistage electron multiplier forsucceeding stages is conventional and therefore needs no further explanation. Ultimately, the multiplied stream of electrons is collected by the electrode 25 and may be conducted to a suitable output circuit for ultilization.

Having reference now to Fig. 3, there is disclosed a modified form of the invention wherein use is made of a plurality of box-type multiplier electrodes for the higher multiplier stages. The first stage electrode 32 is of the same genera! character and configuration as the first stage electrode it of Fig. 1. Likewise, it is disposed in the cathode aperture l3 in such a manner that a portion of it extends into the space contiguousto the photosensitive surface of the cathode and another portion into the space contigu ous to the other surface of the cathode.- If desired,- this electrode also may be provided with a substantially cylindrical open-bottomed grid 33; electrically connected to the electrode and interposed between it and the photosensitive surface of the cathode.

The second stage multiplier electrode 34 has two opposed openings and a generally hollow configuration and is disposed coaxially with the firststage electrode 32. An electrode similar to the electrode 22 of Fig. 1- may be used or one having a somewhatconical shape as illustrated in Fig. 3 may be satisfactory. The relationship betweenelectrodes 32 and 34 is such that the lower portionof the former extends somewhat inside of the upper opening of the latter. The upper opening of the electrode 34 maybe provided with an annular screen 35 electrically connected to this electrode and interposed between the

electrodes

32 and 34.

Adjacent the lower opening of the electrode 34, there is disposed the first one 36 of a plurality of conventional box-type multiplier electrodes. In the structure illustrated in Fig. 3, five such electrodes are provided and, communicating with the last one 31 of these electrodes, there is an electron collecting electrode 38. If desired, each of the box-type electrodes such as 36 may be provided with a screen such as 39, mounted at the respective electrode entrances.

The operation of the form of the invention shown in Fig. 3 is substantially similar to the described operation of the apparatus of Fig. 1. Briefly, the photoelectrons emitted by the photosensitive surface of'the cathode i2 are accelerated by the first stage screen 33 and electron multiplying electrode 32 so that they are caused to impinge with considerable velocity upon the multibox-like stages is effected in a well known manner.

Still another form of the invention is illustrated in Fig. 4. In this case there is disposed in I alignment with the cathode aperture l3 a first stage multiplier electrode 4|, the major portion of which extends into the space contiguous to the photosensitive surface of the cathode. This electrode has a conical surface configuration with the apex directed toward the space contiguous to the other side of the cathode [2. The electrode 4| also may be provided with an open-bottomed substantially cylindrical screen 42 interposed between this electrode and the photosensitive surface of the cathode l2.

The first one43 of a series of box-type electron 2o multiplyin gelectrodes is located so that the enl trance openingthereof is in substantial alignment with the cathode aperture lt; Five of such multiplier electrodes are provided, the last one 44 of which has located adjacent its exit opening an '2 electron collecting electrode 55. Each of the boxtype multiplier electrodes, suchas 42 may be pro- "vided with a screen such as 46; located at the respective entrance openings thereof. 7 I I f The operation of the apparatus illustrated in Fig. 4 is deemed obvious and, therefore, requires no detailed description thereof. As in other forms of the invention, the positioning and confi guration of the first stage multiplier electrode 4| W insures the acceleration thereto Of'PhOtOGlBOtIOIlS from any point on the relatively extensive surface of the cathode l2. By reason particularly of the configuration of the. electrode 4| there are required no other electrodes of specialforms. The

remaining multiplier electrodes may be the con-"'4 yentional box-type electrodes as illustrated.

While there has been described what, at prescut, is considered the preferred embodiment of the invention, it will be obvious to those skilled in 'the art that various changes and modifications '4' 7 What is claimed is: l. A phototube multiplier comprising, a substantially flat photosensitive cathode having a centrally disposed aperture, a; secondary electron emissive multiplier electrode having a portion disposedin the space contiguous to the photosensitive surface. of said cathode and in alignment withsaid aperture and another portion disposed in the space contiguous to the opposite surface of said cathode, and an electron collecting electrode "6 disposed in the space contiguous to said opposite surface of said cathode and in communication with said multiplier electrode.

' 25A' phototube multiplier comprising, a substantially fiat photosensitive cathode having e 6 centrally disposedaperture, a-secondary electron emissive multiplier electrode having aportion disposed in the space contiguous to the photo'- sensitive surface of said cathode and inalignment with said aperture, said electrode having a sub-"f stantially circular cross sectionalarea in aplane parallel to the plane ofsaid cathode, a plurality of additional secondary electron emissive multiplier electrodes disposed, in the space contiguous scope of the invention. s 50 communication with said cathode aperture, and

an electron collecting electrode disposed in communication with one of said plurality of multiplier electrodes.

3. A phototube multiplier comprising, a cathode having a photosensitive surface and a centrally disposed aperture formed therein, a first annular multiplier electrode disposed axially with respect to said cathode aperture and extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, an electron collecting electrode disposed in spaced relation to said cathode on the side opposite to the photosensitive surface thereof, and a second annular multiplier electrode disposed coaxially with said first multiplier electrode and surrounding the space contiguous to that portion of said first electrode extending into the space contiguous to said opposite cathode surface.

7 4. A phototube multiplier comprising, a cathode'having a substantially flat photosensitive surface and a centrally disposed aperture formed therein, a multiplier electrode having an exterior secondaryelectron emissive surface disposed in alignment with said cathode aperture and having aportion disposed in the space contiguous to the photosensitive surface of said cathode and another portion disposed in the space contiguous to the unsensitized surface of said cathode, a boxtype multiplier electrode disposed in the space contiguous to said opposite surface of said cathode in spaced relation to said cathode aperture and in communication therewith, and an electron collecting electrode disposed in spaced relation to said box-type electrode and in communication therewith.

5. 'A phototube multiplier comprising, a cathode having a photosensitive surface and a centrally disposed aperture formed therein, a first annular multiplier electrode having an exterior concave secondary electron emissive surface disposed axially with respect to said cathode aperture and extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, an electron collecting electrode disposed in the space contiguous to said opposite cathode surface, and a second annular multiplier electrode having an interior concave secondary electron emissive surface disposed coaxially with said first multiplier electrodeand surrounding the space contiguous to that portion of said first electrode extending into the space contiguous to said opposite cathode surface.

6. A phototube multiplier comprising, a cathode'having a photosensitive surface of considerable area and a centrally disposed aperture formed therein, a first plurality of annular multiplier electrodes having exterior concave secondary electron emissive surfaces disposed axially with respect to said cathode aperture, an end one of said first plurality of electrodes extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, an electron collecting electrode disposed adjacent to the other end one ofsaidfirst plurality of electrodes coaxially therewith and having the electroncollecting surface thereof parallel to the plane of said cathode aperture, and a second plurality of annular multiplier to the opposite surface of said cathode and in 1 electrodes having interior concave secondary electron emissive surfaces disposed coaxially with said first plurality of electrodes, each but one of said second plurality of electrodes surrounding the space contiguous to adjacent surfaces of successive ones of said first plurality of electrodes, said one of said second plurality of electrodes surrounding the space contiguous to the end portion of the other end one of said first plurality of electrodes and also the space contiguous to said collecting electrodes.

7. A phototube multiplier comprising, a substantially fiat cathode electrode having a photosensitive surface of considerable, area and a centrally disposed aperture formed therein, a first plurality of annular multiplier electrodes having exterior concave secondary electron emissive surfaces disposed axially with respect to said cathode aperture and perpendicularly to the plane of said cathode, an end one of said first plurality of electrodes extending through said cathode aper ture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, a substantially flat electron collecting electrode disposed adjacent to the other end one of said first plurality of electrodes coaxially therewith and having the electron collecting surface thereof parallel to said cathode, a second plu rality of annular multiplier electrodes having interior concave secondary electron emissive surfaces disposed coaxially with said first plurality of electrodes, each but one of said second plurality of electrodes surrounding the space contiguous to adjacent surfaces of successive ones of said first plurality of electrodes, said one of said second plurality of electrodes surrounding the space contiguous to the end portion of the other end one of said first plurality of electrodes and also the space contiguous to said collecting electrode, and a plurality of cylindrical screens electrically connected respectively to said multiplier electrodes and interposed between said respective electrodes and the immediately preceding electrodes.

8. A phototube multiplier comprising, a cathode having a photosensitive surface and a centrally disposed aperture formed therein, a first annular multiplier electrode having an exterior concave secondary electron emissive surface disposed axiall with respect to said cathode aperture and extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, a second annular multiplier electrode having two oppositely disposed openings and arranged coaxially with said first multiplier electrode with one of said openings surrounding the space contiguous to that portion of said first multiplier electrode extending into the space contiguous to said opposite cathode surface and having an interior secondary electron emissive surface, a box-type multiplier electrode disposed adjacent to the other opening of said second annular electrode, and an electron collecting electrode disposed in spaced relation to said box-type electrode and in communication therewith.

9. A phototube multiplier comprising, a substantially flat cathode electrode having a photosensitive surface of considerable area and a centrally disposed aperture formed therein, a first annular multiplier electrode having an exterior concave secondary electron emissive surface disposed axially with respect tosaid cathode aper- 8 ture, perpendicularly to the plane of said cathode and extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode and also into the space contiguous to the opposite surface of said cathode, a second annular multiplier electrode having two opposed openings and a generally hollow onfiguration disposed coaxially with said first multiplier electrode with one opening thereof surrounding the space contiguous to that portion of said first multiplier electrode extending into the space contiguous to said opposite cathode surface and having an interior secondary electron emissive surface, a plurality of serially arranged box-type multiplier electrodes, an end one of said plurality of electrodes being disposed adjacent to the other opening of said second annular electrode, an electron connecting electrode disposed adjacent to the other end one of said plurality of box-type electrodes, and a plurality of screens electrically connected respectively to said multiplier electrodes and interposed between said respective electrodes and the immediately preceding electrodes.

10. A phototube multiplier comprising, a cathode having a substantially flat photosensitive surface and a centrally disposed aperture formed therein, a multiplier electrode having a conical exterior secondary electron emissive surface disposed in alignment with said cathode aperture in the space contiguous to the photosensitive surface of said cathode and with the apex of said electrode adjacent to said cathode aperture, a box-type multiplier electrode disposed in the space contiguous to the opposite surface of said cathode adjacent to said cathode aperture, and an electron collecting electrode disposed in spaced relation to said box-type electrode and in communication therewith.

11. A phototube multiplier comprising, a substantially fiat cathode electrode having a photosensitive surface of considerable area and a centrally disposed aperture formed therein, a multiplier electrode having a conical exterior secondary electron emissive surface disposed axially with respect to said cathode aperture and perpendicularly to the plane of said cathode in the space contiguous to the photosensitive surface of said cathode and with the apex of said multiplier electrode adjacent to said cathode aperture, a plurality of serially arranged box-type multiplier electrodes disposed in the space contiguous to the opposite surface of said cathode, an end one of said plurality of electrodes being disposed adjacent to said cathode aperture, an electron collecting electrode disposed adjacent to the other end one of said plurality of box-type electrodes, and a plurality of screens electrically connected respectively to said multiplier electrodes and interposed between said respective electrodes and the immediately preceding electrodes.

LOZURE G. WOLFGANG.

REFERENCES CITED The following references are of record in the Snyder June 27, 1939