US1841033A - Photo-electric tube - Google Patents

Description

Jan. 12, 1932. H. E. IVES PHOTO ELECTRIC TUBE Original Filed Aug. 20.

0 20 40 60' 30 ANGLE 0F INCIDENCE //7 van/0r: Herbs/2 T/ves m. A #y Patented Jan. 12, 1932:

UNITED STATES PATENT OFFICE HERBERT E. 1m, MONTCLAIB, JERSEY, ASBIGNOB '10 WESTERN ELECTRIC COMPANY, INCORPORATED, 0] NEW YORK, N. Y A CORPORATION 01 NEW YORK PHOTO-ELECTRIC TUBE Application filed August .20, 1925, Serial No. 51,308. Renewed June 9, 1931.

This invention relates to iinprovements in electro-optical apparatus and-particularly to photo-electric cells.

An object of the invention is to provide a light sensitive cell which is highly eflicent in the generation of photo-electric currents.

The invention relates to photoelectric cells of the type in which the incident light is effective not only at the place on the cathode where it is incident but at one or more other ode is a coating upon a reflecting1 surface, referably a metallic surface who may be ighly polished, the cathode coatin of light sensitive material being so thin t at light passes therethrough without appreciable absorption. The invention also rovides a cell structure in which substantia y all of the so light reaches the cathode at a h1 h angle of incidence and is many times re ected from one portion of the cathode to another.

Referring to the drawings, Fig. 1 shows a photo-electric cell representing one embodiment of the invention.

Fig. 2 isa cross-sectional showing of the cell re resented in Fig. 1, the cross-section bein ta on along the line 22'.

igure 3 is a modification of Figs. 1 and 2 of iral cross-section.

showin the cathode in the form of connect ed ara lel plates. ig. 5 illustrates a cell with the cathode in the form of convergent plates.

Fig. 6 shows curves giving the relation between the angles of incidence of the light rays and the resulting hoto-electric current.

, It has been found at the alkali metals when placed in a well evacuated chamber quickl cover with an extremely thin coating al points of the chamber with a photosensitive layer. This coating process is known as spontaneous deposition.

In a preferred embodiment of the invention the light sensitive cathode is coated spontaneously with a thin film of an alkali metal such as sodium, potassium, rubidium,

or caesium. Of these metals caesium has places to which the light is reflected. The. invention provides a cell in which the cath anode 11 are permanently sealed in the arbor and shows the cathode in the form of a plate been found to trio eflect.

Referring to Fig. 1 there is shown one form of construction for carrying out the invention. The cell shown in Fig. 1 comprises an evacuated glass vessel 1, into which are sealed the electrodes 8 and 11. As shown the cell consists of a cylindrical bulb with'a comparatively long neck of smaller diameter. The drawn out portion of the cell is reentrant to provide the usual sealing-in portions 2 and 3 through which the conductors 4 and 5 pass. Sealed in the portions 2 and 3 are the-electrode supporting wires 6 and 7. The supporting wire 7 also serves as a conducting means to the cylindrical cathode 8. For the purpose of main give the greatest photo-electaming the supporting and conducting wires equally spaced and to provide a comparatively rigid structure, an arbor 9 of glass or other suitable insulating material is provided. W es 6 and 7 which support and make contact with the cathode 8 as well as wire 10 which supports and contacts with the central 9. Other forms of mounting and contacting with the electrodes such as are well-known in the art may be employed without departing from the purpose and spirit of the invention.

As shown in Fig. 1 the cathode 8 consists of a metal plate turned into the form of an incomplete cylinder. The opening 12 between the edges of the cathode is for the purpose of allowing the light beams to impinge upon the interior light sensitive surface of the cathode. The cathode may be of any material, but is preferably metallic. It has been found from experiment that a platinum plate which is capacable of retaining a high polish provides a very eflicient base for the coating of the light sensitive substance.

The preferred method of spontaneously coating the cathode 8 with a .thin film of a light sensitive substance, such as caesium, is that described in the Astro-Physical Journal, Volume LX No. 4,'November 1924. It is to be noted that the spontaneous deposition of the alkali metal appears to have no effect on the color or surface character of the underlying plate. Accordingly when a highly substance does not affect this polish. Ad-

Astrovantage is taken of this fact to provide multiple reflection of the light rays as Wlll appear hereinafter. The thickness of the coatin may be regulated as described in the Thysical Journal, Volume LX No. 4, November, 1924.

The anode 11 may consist of any suitable metal preferably tungsten. Fig. 1 shows the anode in the form of a 'rod but it is to be understood that other forms may be emloyed such as, for example, a cylindrical orm or a flat plate form.

Fig. 2 shows a cross-section of the elements of the cell illustrated in Fig. 1 and discloses the manner in which the cell is employed in conjunction with an optical s stem to produce the enhanced photo-electric effect. This figure shows a source of light 13 which,'by means of an appropriate optical system represented by the lens 14, causes the rays of li ht 15 to enter the opening 12 between the erfges of the cylindrical cathode 8 in such a manner as to be incident upon the cathode surface at a very high angle. As a result of thus causing the rays to impinge at a high angle of incldence and because of the cylindrica'l shape of the cathode, a greater photoelectric current is produced than has heretofore been possible. For a given intensity of light from the source 13 this result is a direct function of the angle of incidence of the light rays.

Fig. 6shows themanner in which the photo electric efl'ect varies with the angle of incidence. This figure is the same as Fig. 5 of the article appearing in the Astro-Physical Journal referred to hereinbefore. In this fi re the abscissae represent various angles 0 incidence of the light rays upon the light sensitive surface, while the ordinates represent the corresponding currents for a given potential impressed upon the anode of a photoelectric cell employing a thin film of light sensitive material deposited upon a polished surface. Curve A shows the angle versus current relation when the light sensitive substance is in the form of a thin, spontaneously de osited film on a polished platinum plate. gurve B shows this relation when the light sensitive substance forms a solid layer. It will be observed from these curves therefore that the photo-electric effect obtainable from extremely thin layers is much greater than the effect obtained from comparatively thick layers. It will also be observed that the photo-electric current increases rapidly with the angle of incidence until a maximum is reached the rate of increase being very large for thin films.

From a consideration of these curves, therefore, it is seen that to produce the greatest photo-electric efiect in a given cell fora '85, the maximum current being obtained at an'angle of incidence of approximately 7 5- Wh1le light directed upon a light sensitive surface at a high angle of incidence produces a large photoelectric current, a still further increase is realized when employing in addition a light sensitive surface adapted for multiply reflecting the light incident thereon. Thus by utilizing a photo-electric cell such as shown in Fig. 1 with a thin spontaneously depositing coating of alkali material, such as caesium, on a highly polished platinum plate together with means for allowing the light rays to be incident at the appropriate angle, the maximum eflfect is produced. As may be gathered from an inspection of Fig. 2 because of the highly polished character of the inner surface of cathode 8, and because of its cylindrical structure, each ray is multiply reflected on'the light sensitive surface at a high angle.

Fig. 3 shows a modification of Figs. 1 and 2 with a plate cathode of spiral cross-section. The cathode 16 may be of any suitable metal capable of retaining a high polish and oi being cleaned-by electron bombardment as is well-known in the art. The light sensitive film may be of caesium, rubidium, or other alkali metal. It will be noted in the arrangement of Fig. 3 that for a given cathode area a greater reflecting power is retained, thus proportionately increasing the photo-electri( eflect.

Fig. 4 shows another modification in whicl the cathode consists of 2parallel plates 17 and 18 electrically connected by the conductoi 19. Instead of a central anode in the forn of a wire rod such as shown in Figs. 1, 2 and 3, an anode in the form of an incom plete cylinder 20 is employed. The lighi from source 21 enters through the opening 23 and is focused by means oflens 22 upor the plates 17 and 18 at the optimum angle 0: incidence. Because, of the parallel arrange ment of the cathode plates, the angle of inci dence and reflection is constant. If desire( the wire 19 may be replaced by a flat plati of the same material as plates 17 and 18 anr covered with the same light sensitive sub stance, thus providing further reflecting power for the light rays reflected upon th plates 17 and 18.

Fig. 5 shows a still further modification o: the electrodes. 11 this case an incompleti cylind cal anod 25 is used similar to tha reflections obtaina 1e with such an arrange.

ment.

From the foregoing description it will be seen therefore that applicant has produced a photo-electric cell in which advantage is taken of the increased photo-electric effect produced by the multiple reflecting power of the cathode plates together with means for causing the light rays to be incident upon these plates at a very steep angle.

What is claimed is:

1. A photoelectric cell comprising an anode, and a cathode comprising a highly polished surface thinly coated with a transparent light electrical active film which surface specularly reflects light incident thereon, the photoelectric effect being at a maximum when the light which actuates the cell is incident upon the electrode surface within the range of angles of incidence between 40 and 85.

2. A photoelectric cell comprising an anode, and a cathode comprising a surface coated with a transparent light electrical active film, the photoelectric effect being at a maximum when the light which actuates the cell is incident upon the cathode surface within the range of angles of incidence between 40 and 85.

3. A photoelectric cell comprising an anode, and a cathode comprising a surface coated with a transparent light electrical active film, the photoelectric effect being at a maximum when the light which actuates the cell is incident upon the cathode surface at an angle of incidence of the order of 75.

4. A photoelectric cell comprising an anode, and a cathode comprising a highly polished surface coated with a transparent light electrical active film, which surface multiply reflects light incident thereon, the photoelectric effect being at a maximum when the light which actuates the cell is incident u on the cathode surface within the range angles of incidence between and 85.

5. A photoelectric cell comprising an anode, and a cathode comprising a surface coated with a transparent li ht electrical active film, the photoelectric e ect being at a maximum when the light which actuates the cell is incident upon the cathode surface within the range of angles of incidence between 40 and 85, said cathode reflecting light incident at a. certain angle within said range upon one portion of the surface thereof to another portion of said surface.

6. A photoelectric cell comprising an anode, and a cathode having a plurality of portions,

the light sensitive surfaces of which portions are opposite each other, whereby when the activating light is incident upon one of said surfaces at an angle of incidence within the range of from 40 to 85 the incident light will be reflected to the sensitive surface of the other of said portions, the photoelectric effect being at a maximum when the incident light is within said range.

7. A photoelectric cell comprising an anode, and a cathode having a plurality of extended plane portions, the light sensitive surfaces of which ortions are opposite each other whereby wiien the activating light is incident upon one of said surfaces at an angle of incidence within the range of from 40 to 85 the incident light will be reflected to the sensitive surface of the other of said portions, the photoelectric effect being at a maximum when the incident light is within said range.

In witness whereof, I hereunto subscribe my name this 17th day of August, A. D., 1925.

HERBERT E. IVES.

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