US3829219A
Expired / Lapsed
US
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Shearing interferometer
Assignee: Northrop Grumman Guidance and Electronics Co Inc
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Filing: 1973-03-30
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Granted: 1974-08-13
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Expires: 1993-03-30
Abstract
Abstract A shearing interferometer for producing a shearing interferogram of a wavefront being converged to a focal point. In a first embodiment in which the wavefront is comprised of monochromatic radiation, two diffraction gratings having slightly different line spacings are placed near the focal point of the wavefront. The diffraction gratings produce two first diffraction orders at two slightly different angles which result in a shearing interferogram in the region of overlap. The resulting shearing interferogram yields wavefront information in one direction. Complete wavefront information in two directions may be obtained by shearing the wavefront in two orthogonal directions. This is accomplished by placing two additional diffraction gratings having slightly different line spacings near the focal point of the wavefront and in an orthogonal direction relative to the first two diffraction gratings. In a second embodiment in which the wavefront is comprised of white light, a blazed diffraction grating is introduced into the interferogram. Both the monochromatic and white light interferometers may use heterodyning, real time phase detection. When heterodyning phase detection is used, the irradiance of the interferogram is modulated sinusoidally by translating sideways at least one of the diffraction gratings.
Inventors
- 👤 J Wyant
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 23:20
CPC Classifications
G; G01; G01B; G01B9/00; G01B9/02; G01B9/02097; G01B9/02098; G01B11/00; G01B11/16; G01B11/18; G01J; G01J9/00; G01J9/02; G01J9/0215; G01B2290/00; G01B2290/30
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
147 words
A system for producing a shearing interferogram of a wavefront being converged to a focal point and comprising: a. a first diffraction grating positioned in the wavefront in proximity to said focal point for producing a first, n order, diffracted beam, said first diffraction grating having a first line spacing pattern; and b. a second diffraction grating positioned in the wavefront and in proximity to said focal point and said first diffraction grating for producing a second, n order, diffracted beam wherein said first and second n order diffracted beams are the same order, said second diffraction grating having a second line spacing pattern which is different from said first line spacing pattern such that said second diffracted beam is angularly displaced relative to said first diffracted beam but has a region of overlap with said first diffracted beam in which a lateral shearing interferogram is produced.
Claim 2
Independent Claim
147 words
A system for producing a shearing interferogram of a wavefront being converged to a focal point and comprising: a. a first diffraction grating positioned in the wavefront in proximity to said focal point for producing a first, n order, diffracted beam, said first diffraction grating having a first line spacing pattern; and b. a second diffraction grating positioned in the wavefront and in proximity to said focal point and said first diffraction grating for producing a second, n order, diffracted beam wherein said first and second n order diffracted beams are the same order, said second diffraction grating having a second line spacing pattern which is different from said first line spacing pattern such that said second diffracted beam is angularly displaced relative to said first diffracted beam but has a region of overlap with said first diffracted beam in which a lateral shearing interferogram is produced.
Claim 3
Dependent Claim
24 words
A system as set forth in claim 1 wherein said first diffraction grating and said second diffraction grating are both produced on one medium.
Claim 4
Dependent Claim
186 words
A system as set forth in claim 1 wherein the wavefront is sheared in two orthogonal directions and wherein the system further includes: a. a third diffraction grating positioned in the wavefront in proximity to said focal point for producing a third, n order, diffracted beam, said third diffraction grating having a third line spacing pattern which is positioned substantially perpendicular to said first and second line spacing patterns; and b. a fourth diffraction grating positioned in the wavefront in proximity to said focal point for producing a fourth, n order, diffracted beam wherein said third and fourth diffracted beams are the same order, said fourth diffraction grating having a fourth line spacing pattern which is positioned substantially perpendicular to said first and second line spacing patterns and which is different from said third line spacing pattern to produce a fourth, n order, diffracted beam which is angularly displaced relative to said third, n order, diffracted beam in which a second lateral shearing interferogram is produced, whereby the wavefront is sheared in two orthogonal directions to allow complete wavefront information in two directions to be obtained.
Claim 5
Dependent Claim
32 words
A system as set forth in claim 3 wherein said first diffraction grating, said second diffraction grating, said third diffraction grating and said fourth diffraction grating are all produced on one medium.
Claim 6
Dependent Claim
39 words
A system as set forth in claim 1 wherein the system uses heterodyning, real time phase detection and includes means for translating sideways at least one of said diffraction gratings in a direction perpendicular to its line spacing pattern.
Claim 7
Dependent Claim
46 words
A system as set forth in claim 5 wherein the system includes means for electronically detecting the irradiance of the interferogram at a plurality of points in the interferogram, whereby phase differences in the irradiation of the interferogram between said plurality of points may be determined.
Claim 8
Dependent Claim
25 words
A system as set forth in claim 6 wherein said detecting means includes an array of photodetectors positioned to detect the irradiance of the interferogram.
Claim 9
Dependent Claim
16 words
A system as set forth in claim 6 wherein said n orders are first diffraction orders.
Claim 10
Dependent Claim
43 words
A system as set forth in claim 1 wherein the system is adapted to be utilized with a wavefront comprised of white light and wherein a first achromatic diffraction grating is positioned in the interferogram produced by said first and second diffraction gratings.
Claim 11
Dependent Claim
67 words
A system as set forth in claim 9 wherein: a. said first diffraction grating has a first line spacing pattern at a first frequency f1; b. said second diffraction grating has a second line spacing pattern at a frequency f2, different from f1; and c. said first achromatic diffraction grating has a line spacing pattern at a frequency which is substantially the average of f1 and f2.
Claim 12
Dependent Claim
216 words
A system as set forth in claim 10 wherein the wavefront is sheared in two orthogonal directions and wherein the system further includes: a. a third diffraction grating positioned in the wavefront in proximity to said focal point for producing a third, n order, diffracted beam, said third diffraction grating having a third line spacing pattern at a frequency f3 which is positioned perpendicular to said first and second line spacing patterns; b. a fourth diffraction grating positioned in the wavefront in proximity to said focal point for producing a fourth, n order, diffracted beam wherein said third and fourth diffracted beams are the same order, said fourth diffraction grating having a fourth line spacing pattern at a frequency f4, different from the frequency f3, which is positioned substantially perpendicular to said first and second line spacing patterns to produce a fourth, n order, diffracted beAm which is angularly displaced relative to said third, n order, diffracted beam and which has a region of overlap with said third, n order, diffracted beam in which a second lateral shearing interferogram is produced; and c. a second achromatic diffraction grating positioned in said second lateral shearing interferogram, said second achromatic grating having a line spacing pattern at a frequency which is substantially the average of f3 and f4.
Claim 13
Dependent Claim
32 words
A system as set forth in claim 11 wherein said first diffraction grating, said second diffraction grating, said third diffraction grating and said fourth diffraction grating are all produced on one medium.
Claim 14
Dependent Claim
67 words
A system as set forth in claim 12 wherein the system uses heterodyning, real time, phase detection and includes means for translating said photographic medium in a direction such that it has a component of motion perpendicular to said line spacing patterns of said first and second diffraction gratings and a component of motion perpendicular to said line spacing patterns of said third and fourth diffraction gratings.
Claim 15
Dependent Claim
16 words
A system as set forth in claim 13 wherein said n orders are first diffraction orders.
Claim 16
Dependent Claim
94 words
A system as set forth in claim 1 and further including: a. a first optical system which is to be tested by the system and positioned to produce the wavefront; and b. a second optical system positioned in said lateral shearing interferogram to form an image of the exit pupil of said first optical system in an interference plane whereby said first and second diffraction gratings result in two laterally displaced images of the exit pupil in said interference plane but with a region of overlap in which a lateral shearing interferogram is produced.
Claim 17
Dependent Claim
47 words
A system as set forth in claim 15 wherein the system includes means for electronically detecting the irradiance of the interferogram at a plurality of points in the interference plane, whereby phase differences in the irradiation of the interferogram between said plurality of points may be determined.
Claim 18
Dependent Claim
16 words
A system as set forth in claim 16 wherein said n orders are first diffraction orders.
Claim 19
Dependent Claim
16 words
A system as set forth in claim 1 wherein said n orders are first diffraction orders.
Claim 20
Dependent Claim
16 words
A system as set forth in claim 1 wherein said n orders are second diffraction orders.
Claim 21
Dependent Claim
33 words
A system as set forth in claim 1 wherein said first line spacing pattern is at a frequency f1, and said second line spacing pattern is at a frequency f2, different from f1.
Claim 22
Dependent Claim
54 words
A system as set forth in claim 1 wherein said first line spacing pattern and said second line spacing pattern are both at the same frequency, and said second line spacing pattern is different from said first line spacing pattern in that it is rotated slightly with respect to said first line spacing pattern.
Claim 23
Independent Claim
157 words
A system for producing a shearing interferogram of a wavefront and comprising: a. first diffraction means positioned in the wavefront for producing a first, n order, diffracted beam; b. second diffraction means positioned in the wavefront in proximity to said first diffraction means for producing a second, n order, diffracted beam wherein said first and second n order beams are the same order and which second beam is angularly displaced relative to said first, n order, diffracted beam, but having a region of overlap with said first, n order, diffracted beam in which a lateral shearing interferogram is produced, said first and second n order diffracted beams being the same order; and c. means for detecting the irradiance of the lateral shearing interferogram produced by said first and second diffracted beams at a plurality of locations in the interferogram, whereby phase differences between the plurality of locations may be ascertained to determine the shape of the wavefront.
Claim 24
Independent Claim
157 words
A system for producing a shearing interferogram of a wavefront and comprising: a. first diffraction means positioned in the wavefront for producing a first, n order, diffracted beam; b. second diffraction means positioned in the wavefront in proximity to said first diffraction means for producing a second, n order, diffracted beam wherein said first and second n order beams are the same order and which second beam is angularly displaced relative to said first, n order, diffracted beam, but having a region of overlap with said first, n order, diffracted beam in which a lateral shearing interferogram is produced, said first and second n order diffracted beams being the same order; and c. means for detecting the irradiance of the lateral shearing interferogram produced by said first and second diffracted beams at a plurality of locations in the interferogram, whereby phase differences between the plurality of locations may be ascertained to determine the shape of the wavefront.
Claim 25
Dependent Claim
215 words
A system as set forth in claim 22 wherein the wavefront is sheared in two orthogonal directions and wherein the system further includes: a. a third diffraction means positioned in the wavefront for producing a third, n order, diffracted beam, said third, n order diffracted beam being diffracted in a direction substantially perpendicular to the direction of diffraction of said first and second diffracted beams; b. a fourth diffraction means positioned in the wavefront in proximity to said third diffraction means for producing a fourth, n order, diffracted beam wherein said third and fourth n order beams are the same order and which fourth beam is diffracted in a direction substantially perpendicular to the direction of diffraction of said first and second diffracted beams and is angularly displaced relative to said third, n order, diffracted beam but having a region of overlap with said third, n order diffracted beam in which a lateral shearing interferogram is produced, said third and fourth n order diffracted beams being the same order; and c. means for detecting the irradiance of the lateral shearing interferogram produced by said third and fourth diffracted beams at a plurality of locations in the interferogram, whereby phase differences between the plurality of locations may be ascertained to determine the shape of the wavefront.
Claim 26
Dependent Claim
19 words
A system as set forth in claim 23 wherein each of said detecting means includes an array of photodetectors.
Claim 27
Dependent Claim
17 words
A system as set forth in claim 22 wherein said detecting means includes an array of photodetectors.
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) | 1977-08-12 | 1978-02-11 | 1978-08-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-08-12 | 1982-02-11 | 1982-08-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-08-12 | 1986-02-11 | 1986-08-13 | $7700.00 | Window Closed / Lapsed |