US3836256A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Interferometer for testing telescope optics
Assignee: Raytheon Co
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Filing: 1972-05-08
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Granted: 1974-09-17
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Expires: 1992-05-08
Abstract
Abstract This is an interferometer of Twyman-Green type adapted for testing the optics of a stellar telescope. Coherent light from a source, such as a star, through the telescope is collimated and divided into a reference beam, and a main beam, which are, respectively, a fractional cross-sectional area of the collimated beam, and the remaining cross-sectional area thereof. The reference beam is expanded to be the same diameter as the main beam by an afocal telescope and the two are then combined in superimposed relation. The optical path lengths of the reference and main beams are made approximately the same and means is provided for cyclically lengthening and shortening the length of one of them at a predetermined rate so that one of the paths is cyclically shorter than, equal to and longer than the other. The combined beams are filtered and focussed to image the telescope pupil (usually the primary mirror) in a plane, and at least a pair of photodetectors in this plane detect the light respectively at different points on the image, and produce signals proportional to the light received. The signals from the respective photodetectors are compared as to phase when the signal is sinusoidal, or time delay when the signal is a pulse, to detect the deviation of the wavefront exiting the telescope from the ideal wavefront, such deviation being linearly proportional to aberrations of the telescope resulting from poor optical figure on the individual optical elements or misalignment of the telescope optics.
Inventors
- 👤 W Peters
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 15:16
CPC Classifications
G; G01; G01J; G01J9/00; G01J9/02
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
238 words
An interferometer for testing the optics of a telescope for alignment and aberrations, comprising means selecting the light from a single source of at least partially coherent light viewed through a telescope, means collimating said light into a beam, a first transparent plate at an angle across the collimated beam at the pupil of the telescope with a reflective dot on the surface of the plate on which the collimated beam impinges, said dot being within the circumference of the beam area and a fraction of the cross-sectional area of the collimated beam, so that the collimated beam is separated into a reference beam consisting of a fractional cross-sectional area of the collimated beam reflected by the dot and a main beam consisting of the remaining cross-sectional portion of the collimated beam passing through the transparent plate, means directing the reference and main beams along separate paths to combining means from which the beams emerge in superimposed relation, means expanding the reference beam to be substantially the same diameter as the main beam at the combining means, means for changing the length of one of said separate paths of the reference and main beams for making said paths alternatively unequal and substantially equal, means focussing the superimposed beams, and means detecting and comparing the interferometrically produced light at one selected area in the telescope relay pupil plane of the focussing means with the light in another area thereof.
Claim 2
Dependent Claim
238 words
An interferometer for testing the optics of a telescope for alignment and aberrations, comprising means selecting the light from a single source of at least partially coherent light viewed through a telescope, means collimating said light into a beam, a first transparent plate at an angle across the collimated beam at the pupil of the telescope with a reflective dot on the surface of the plate on which the collimated beam impinges, said dot being within the circumference of the beam area and a fraction of the cross-sectional area of the collimated beam, so that the collimated beam is separated into a reference beam consisting of a fractional cross-sectional area of the collimated beam reflected by the dot and a main beam consisting of the remaining cross-sectional portion of the collimated beam passing through the transparent plate, means directing the reference and main beams along separate paths to combining means from which the beams emerge in superimposed relation, means expanding the reference beam to be substantially the same diameter as the main beam at the combining means, means for changing the length of one of said separate paths of the reference and main beams for making said paths alternatively unequal and substantially equal, means focussing the superimposed beams, and means detecting and comparing the interferometrically produced light at one selected area in the telescope relay pupil plane of the focussing means with the light in another area thereof.
Claim 3
Dependent Claim
55 words
The combination of claim 1 including means comparing the phase of the interferometrically produced light in one of said areas of said telescope relay pupil plane of the focussing means with the phase of the interferometrically produced light in another area thereof and including means producing a signal linearly proportional to a differencE in phase.
Claim 4
Dependent Claim
55 words
The combination of claim 1 including means detecting the peak intensity of light in each of said areas of said relay pupil plane, and means producing a signal linearly proportional to a difference in time between a peak intensity of light in one of the areas and a peak intensity of light in the other.
Claim 5
Dependent Claim
37 words
The combination of claim 1 in which said means for changing the length of one of said paths changes the length between being shorter than, equal to, and longer than the other, cyclically at a uniform rate.
Claim 6
Dependent Claim
41 words
The combination of claim 1 in which said means separating the beam into two beams comprises a plane reflecting surface of smaller diameter than said collimated beam supported in the collimated beam to reflect a portion thereof away at an angle.
Claim 7
Dependent Claim
66 words
The combination of claim 1 in which said combining means comprises a beamsplitter, the paths of the reference beam and main beam being directed to the beamsplitter for one of the beams to be partially transmitted therethrough and the other beam to be partially reflected thereby, and for said partially transmitted and partially reflected portions to leave the beamsplitter in the same direction in superimposed relation.
Claim 8
Dependent Claim
57 words
The combination of claim 6 in which, for optimizing the performance of the interferometer, the beamsplitter is adapted to transmit that portion of the light incident thereon which is 1 -d/D times the amount of incident light, where d is the diameter of the reference beam before expansion and D is the diameter of the main beam.
Claim 9
Dependent Claim
156 words
The combination of claim 1 in which said combining means comprises a second transparent plate having a semireflective beamsplitting coating thereon, said second plate and said means for directing the main and reference beams being positioned for the main beam to impinge on the surface of the second plate having said coating thereon and for the expanded reference beam to impinge on the opposite surface so as to pass through the second plate and emerge in superposed relation with the portion of the reference beam reflected from the semireflected coating whereby the main beam passes through only the first plate and the reference beam passes through only the second plate, the first and second plates having substantially the same dispersion and thickness and being at substantially the same angle to the collimated beam and the reference beam respectively, whereby the optical path lengths of the main and reference beams through the respective plates are substantially equal.
Claim 10
Dependent Claim
35 words
The combination of claim 8 in which the first and second plates are different portions of a single transparent plate, the reflective dot being on one portion and the semireflective coating being on the other.
References Cited (Backward Citations)
US3567324A
Cited
US3694088A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-09-16 | 1978-03-18 | 1978-09-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-09-16 | 1982-03-18 | 1982-09-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-09-16 | 1986-03-18 | 1986-09-17 | $7700.00 | Window Closed / Lapsed |