US3567948A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for improving the quantum efficiency of phototubes
Assignee: United States Department of the Navy
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Filing: 1969-04-14
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Granted: 1971-03-02
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Expires: 1989-04-14
Abstract
Abstract An end-on photomultiplier tube has a fused quartz dome covering its light-receiving face plate or window and further has its photocathode interfaced with the window and with the tube vacuum. The dome is a partial hemisphere so shaped that, in combination with the window thickness, the two members form a true hemisphere centered on the cathode. An incident light beam passing through the dome and directed onto the cathode center is reflected back into the dome from both the inner and outer interfaces of the cathode. The exterior surface of the dome lying in the path of these reflected beams is aluminized and, since the radius of curvature of the dome is centered on the cathode, these reflected beams are normal to the aluminized surface and thus re-reflected and reimaged back onto the cathode center. The arrangement achieves quantum efficiency gains by permitting a multiple photon traversal of the cathode and by controlling the angle of incidence to promote maximum interface reflectance. Also the reduction in size of the effective photocathode area minimizes photomultiplier dark current.
Inventors
- 👤 John B Oke
- 👤 Rudolph E Schild
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 11:14
CPC Classifications
H; H01; H01J; H01J40/00; H01J40/02; H01J40/04; H01J40/06; H01J43/00; H01J43/04; H01J43/28
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
147 words
Apparatus for measuring light emanating as a beam from a source comprising: a phototube having a light-receiving end; a thin platelike photocathode carried by the tube at its lightreceiving end; a dome member mounted on and covering said light-receiving end; said member having a substantially hemispherical exterior surface with a radius of curvature centered on said photocathode; a portion of said dome member being light-transmissive and said portion being disposed to admit said light beam obliquely along said radius onto said photocathode center; and a portion of said dome member being light reflective and being disposed to reflect back to said photocathode center such fractions of said light beam as initially are reflected onto it from said center, whereby the photoelectrically effective area of said photocathode essentially is limited to its center and said initial and return reflections have Plural opportunities to pass into said effective area.
Claim 2
Dependent Claim
147 words
Apparatus for measuring light emanating as a beam from a source comprising: a phototube having a light-receiving end; a thin platelike photocathode carried by the tube at its lightreceiving end; a dome member mounted on and covering said light-receiving end; said member having a substantially hemispherical exterior surface with a radius of curvature centered on said photocathode; a portion of said dome member being light-transmissive and said portion being disposed to admit said light beam obliquely along said radius onto said photocathode center; and a portion of said dome member being light reflective and being disposed to reflect back to said photocathode center such fractions of said light beam as initially are reflected onto it from said center, whereby the photoelectrically effective area of said photocathode essentially is limited to its center and said initial and return reflections have Plural opportunities to pass into said effective area.
Claim 3
Dependent Claim
26 words
The apparatus of claim 1 wherein said apparatus further includes: a telescope having a focusing lens for imaging its objective on said center of the photocathode.
Claim 4
Dependent Claim
47 words
The apparatus of claim 2 wherein; said light transmissive portion of the dome member is of sufficient area to admit said objective at an angle of incidence greater than about 40* relative to said photocathode, said light reflective portion reimaging said incident beam on said photocathode center.
Claim 5
Dependent Claim
13 words
The apparatus of claim 3 wherein said angle of incidence is about 55*.
Claim 6
Dependent Claim
40 words
The apparatus of claim 3 wherein said tube is a photomultiplier having a flat end wall providing a light-transmissive window, said cathode being disposed internally of the window and interfaced with both the window and the vacuum of the tube.
Claim 7
Dependent Claim
24 words
The apparatus of claim 5 wherein said dome is formed of quartz and said light-reflecting section is an aluminum coating adhered to the quartz.
Claim 8
Independent Claim
131 words
A method if improving the quantum efficiency of a phototube used with a focusing lens for imaging a telescopic objective on the photocathode of the tube, the phototube being of a type in which the photocathode is disposed flushly adjacent a wall of the tube, the method comprising: admitting said focused image obliquely on the center area of said photocathode at an angle of incidence capable of promoting maximum reflection of said image from the interface of the cathode and said tube wall; reimaging such fractions of light as are reflected from said center back onto the center; and whereby the image quality is maintained, the quantum efficiency of the tube being improved by the multiple traversals of the cathode and by minimizing the escape of photons into said tube vacuum.
Claim 9
Independent Claim
131 words
A method if improving the quantum efficiency of a phototube used with a focusing lens for imaging a telescopic objective on the photocathode of the tube, the phototube being of a type in which the photocathode is disposed flushly adjacent a wall of the tube, the method comprising: admitting said focused image obliquely on the center area of said photocathode at an angle of incidence capable of promoting maximum reflection of said image from the interface of the cathode and said tube wall; reimaging such fractions of light as are reflected from said center back onto the center; and whereby the image quality is maintained, the quantum efficiency of the tube being improved by the multiple traversals of the cathode and by minimizing the escape of photons into said tube vacuum.
Claim 10
Dependent Claim
23 words
The method of claim 7 wherein said image is admitted at an angle of incidence relative to said cathode of greater than 40*.
Claim 11
Dependent Claim
10 words
The method of claim 8 wherein said angle is 55*.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-03-01 | 1974-08-31 | 1975-03-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-03-01 | 1978-08-31 | 1979-03-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-03-01 | 1982-08-31 | 1983-03-02 | $7700.00 | Window Closed / Lapsed |