Patent US4344434A successfully refreshed from Google Patents.
US3767307A
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Real time interferometer
Assignee: Northrop Grumman Guidance and Electronics Co Inc
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Filing: 1971-08-30
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Granted: 1973-10-23
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Expires: 1991-08-30
Abstract
Abstract Disclosed is a laser unequal pathlength interferometer for measuring mirror surface figures. Test and reference beams of different wavelengths are used in conjunction with detection apparatus that is responsive to a beat frequency resulting from the combination of the test and reference beams. In a preferred embodiment a single beam is split to provide test and reference beams and a relative Doppler shift is imposed therebetween. An heterodyne circuit in the detection apparatus replaces the beat frequency with a stable carrier frequency before final analysis.
Inventors
- 👤 Bowker J Kent
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 22:45
CPC Classifications
G; G01; G01B; G01B9/00; G01B9/02; G01B9/02001; G01B9/02007; G01B9/02002; G01B9/02003; G01B2290/00; G01B2290/15; G01B2290/70
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
248 words
Interferometer apparatus comprising: a. radiation source means for producing a test beam and a reference beam, said test and reference beams being coherent monochromatic beams of substantially the same wavelength; b. optical test means for directing said test beam toward a reflective test surface and comprising a test diverger means in the path of said test beam for expanding said test beam so as to illuminate a shaped test surface and wherein said test diverger means also collimates returning reflections from said shaped test surface; c. Doppler means for introducing a Doppler frequency shift between said test and reference beams; d. optical combining means for combining said Doppler shifted test and reference beams into an output beam after reflection of said test beam from the test surface; and e. detection means responsive to a beat frequency of said output beam and comprising an output imaging means and an image surface means disposed in the path of said output beam so as to produce interference phonomena on said image surface means, further comprising a plurality of photo-sensitive detectors disposed in different positions on said image surface, said detectors being movable with respect to each other and being for detecting the intensity of said interference phenomena at said different positions by receiving radiation reflected from different locations on said test surface and wherein said detection means further comprises detection circuit means operatively coupled to said plurality of detectors to determine phase relationships among the outputs of said plurality of detectors.
Claim 2
Dependent Claim
248 words
Interferometer apparatus comprising: a. radiation source means for producing a test beam and a reference beam, said test and reference beams being coherent monochromatic beams of substantially the same wavelength; b. optical test means for directing said test beam toward a reflective test surface and comprising a test diverger means in the path of said test beam for expanding said test beam so as to illuminate a shaped test surface and wherein said test diverger means also collimates returning reflections from said shaped test surface; c. Doppler means for introducing a Doppler frequency shift between said test and reference beams; d. optical combining means for combining said Doppler shifted test and reference beams into an output beam after reflection of said test beam from the test surface; and e. detection means responsive to a beat frequency of said output beam and comprising an output imaging means and an image surface means disposed in the path of said output beam so as to produce interference phonomena on said image surface means, further comprising a plurality of photo-sensitive detectors disposed in different positions on said image surface, said detectors being movable with respect to each other and being for detecting the intensity of said interference phenomena at said different positions by receiving radiation reflected from different locations on said test surface and wherein said detection means further comprises detection circuit means operatively coupled to said plurality of detectors to determine phase relationships among the outputs of said plurality of detectors.
Claim 3
Dependent Claim
36 words
Inteferometer apparatus according to claim 1 wherein said radiation source means comprises a radiation source for producing a primary beam and beam splitter means for dividing said primary beam to form said test and reference beams.
Claim 4
Dependent Claim
13 words
Interferometer apparatus according to claim 2 wherein said light source comprises a laser.
Claim 5
Dependent Claim
25 words
Interferometer apparatus according to claim 1 wherein said Doppler means comprises a retroreflector means for introducing said Doppler shift between said test and reference beams.
Claim 6
Dependent Claim
35 words
Interferometer apparatus according to claim 4 wherein said retroreflector means comprises a retroreflector element, a mirror disposed to reflect toward said retroreflector element wave energy received therefrom, and motive means for producing relative movement therebetween.
Claim 7
Dependent Claim
22 words
Interferometer apparatus according to claim 5 wherein said mirror is fixed and said motive means produces reciprocating movement of said retroreflector element.
Claim 8
Dependent Claim
15 words
Interferometer apparatus according to claim 6 wherein said reciprocating retroreflector element comprises a cat''s eye.
Claim 9
Dependent Claim
16 words
Interferometer apparatus according to claim 6 wherein said reciprocating retroreflector element comprises a translating corner cube.
Claim 10
Dependent Claim
57 words
Interferometer apparatus according to claim 1 wherein said detection circuit means comprises two capacitatively coupled zero crossing detectors, each one operatively associated with one of said photosensitive detectors and responsive thereto, and said detection circuit means further comprises a bistable device that is operatively coupled to said threshold detectors and is set and reset by signals therefrom.
Claim 11
Dependent Claim
40 words
Interferometer apparatus according to claim 9 wherein said detection circuit means further comprises a heterodyne circuit for replacing the beat frequency in the output of said two photosensitive detectoRs with a stable carrier frequency before actuation of said bistable device.
Claim 12
Dependent Claim
27 words
Interferometer apparatus according to claim 10 wherein said detection circuit means further comprises a clock means for measuring the proportional periods of the set and reset modes.
Claim 13
Dependent Claim
26 words
Apparatus according to claim 1 wherein each of said photosensitive detectors comprises photo diode means responsive only to the difference beat frequency in said output beam.
Claim 14
Dependent Claim
212 words
Interferometer apparatus comprising: a. a radiation source means for producing a test beam and a reference beam, wherein both of said beams are monochromatic and coherent and are of different wavelengths; b. optical test means for directing said test beam toward a reflective test surface; c. optical combining means for directing said beams such that said beams combine after said test beam has been reflected by said test surface to form an output beam; and d. detection means responsive to a beat frequency in said output beam and comprising: A. an imaging means with an image surface means disposed in the path of said output beam so as to produce interference phenomena on said image surface means; B. two photosensitive detectors disposed in different positions on said image surface and movable with respect to each other and receiving radiation reflected from different locations on said test surface so as to be responsive to the intensity of said interference phenomena at said positions and C. detection circuit means that comprises: i. two capacitively coupled zero crossing detectors, each one operatively associated with one of said two photosensitive detectors and responsive thereto; and ii. a bistable device that is operatively coupled to said zero crossing detectors and is set and reset by signals therefrom.
Claim 15
Dependent Claim
212 words
Interferometer apparatus comprising: a. a radiation source means for producing a test beam and a reference beam, wherein both of said beams are monochromatic and coherent and are of different wavelengths; b. optical test means for directing said test beam toward a reflective test surface; c. optical combining means for directing said beams such that said beams combine after said test beam has been reflected by said test surface to form an output beam; and d. detection means responsive to a beat frequency in said output beam and comprising: A. an imaging means with an image surface means disposed in the path of said output beam so as to produce interference phenomena on said image surface means; B. two photosensitive detectors disposed in different positions on said image surface and movable with respect to each other and receiving radiation reflected from different locations on said test surface so as to be responsive to the intensity of said interference phenomena at said positions and C. detection circuit means that comprises: i. two capacitively coupled zero crossing detectors, each one operatively associated with one of said two photosensitive detectors and responsive thereto; and ii. a bistable device that is operatively coupled to said zero crossing detectors and is set and reset by signals therefrom.
Claim 16
Dependent Claim
19 words
Interferometer apparatus according to claim 13 wherein said radiation source means comprises a laser subjected to a magnetic field.
Claim 17
Dependent Claim
27 words
Interferometer apparatus according to claim 14 wherein said detection circuit means further comprises a clock means for measuring the proportional periods of the set and reset modes.
Claim 18
Dependent Claim
44 words
Interferometer apparatus according to claim 13 wherein said optical test means comprises a test diverger means for expanding said test beam so as to illuminate a shaped test surface and wherein said test diverger means also collimates returning reflections from said shaped test surface.
Claim 19
Dependent Claim
40 words
Interferometer apparatus according to claim 16 wherein said detection circuit means further comprises a heterodyne circuit for replacing the beat frequency in the output of said two photosensitive detectors with a stable carrier frequency before actuation of said bistable device.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-10-22 | 1977-04-23 | 1977-10-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-10-22 | 1981-04-23 | 1981-10-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-10-22 | 1985-04-23 | 1985-10-23 | $7700.00 | Window Closed / Lapsed |