US5048964A
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Phase-stepping interferometry
Assignee: BTG International Ltd
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Filing: 1989-09-04
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Granted: 1991-09-17
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Expires: 2009-09-04
Abstract
Abstract An interferometric procedure, such as electronic speckle pattern interferometry, involves generating two signals representing the point-by-point variations in intensity of respective patterns of electromagnetic radiation resulting from the interference of first and second beams of such radiation derived from a coherent source, with at least the first beam from each pattern being scattered, before interference with its respective second beam, from a common object surface, and with a corresponding pair of the beams, one for each pattern, having a predetermined relative phase difference of other than a multiple of π; and determining from the two signals values for a datum phase of the radiation at the object surface. Preferably, as a preliminary to this last determination. DC components are removed from the two signals. Conveniently, to simplify the determination, the phase difference is an odd multiple of π/4 or π/2.
Inventors
- 👤 John R. Tyrer
- 👤 Fernando Mendoza-Santoyo
- 👤 David Kerr
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 15:32
CPC Classifications
G; G01; G01B; G01B9/00; G01B9/02; G01B9/02001; G01B9/0201; G01B9/02094
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
102 words
An interferometric method comprising: generating two signals representing point-by-point variations in intensity of respective patterns of electromagnetic radiation resulting from an interference of first and second beams of such radiation derived from a coherent source, with at least the first beam for each pattern being scattered, before interference with its respective second beam, from a common object surface, and with a corresponding pair of the beams, one for each pattern, having a predetermined relative phase difference of other than an integer multiple of π; and determining, from said two signals alone, values for a datum phase of the radiation at said surface.
Claim 2
Dependent Claim
102 words
An interferometric method comprising: generating two signals representing point-by-point variations in intensity of respective patterns of electromagnetic radiation resulting from an interference of first and second beams of such radiation derived from a coherent source, with at least the first beam for each pattern being scattered, before interference with its respective second beam, from a common object surface, and with a corresponding pair of the beams, one for each pattern, having a predetermined relative phase difference of other than an integer multiple of π; and determining, from said two signals alone, values for a datum phase of the radiation at said surface.
Claim 3
Dependent Claim
24 words
A method according to claim 1 wherein, as a preliminary to said datum phase value determination, DC components are removed from said two signals.
Claim 4
Dependent Claim
18 words
A method according to claim 1 or 2 wherein said phase difference is an odd multiple of π/2.
Claim 5
Dependent Claim
36 words
A method according to claim 3 wherein each of said corresponding pair of beams has a phase difference which is the same odd multiple of π relative to said datum phase but of mutually opposite sense.
Claim 6
Dependent Claim
45 words
A method as in claim 3, wherein said determining step includes the steps of: obtaining equations representing said two signals, such that ##EQU6## such that when δ is an odd multiple of π/2, φ=tan.sup.-1 ±I.sub.1 /I.sub.2 ; and solving said equations for said datum phase.
Claim 7
Dependent Claim
38 words
A method as in claim 1, wherein said determining step includes the steps of: obtaining equations representing said two signals, in a way that a phase shift amount becomes ±1; and solving said equations for said datum phase.
Claim 8
Dependent Claim
11 words
A method according to claim 1 wherein said radiation is light.
Claim 9
Dependent Claim
139 words
Interferometric apparatus comprising: means for generating a first signal representing point-by-point variations in intensity I of a pattern of electromagnetic radiation resulting from an interference of first and second beams of such radiation derived from a coherent source, with at least the first beam being scattered from an object surface before interference with the second beam; means for changing the phase of one of said first and second beams by an amount δ other than an integer multiple of π to generate a second signal in like manner to said first signal; means for removing DC components from said first and second signals; and means, responsive only to said first and second signals following DC component removal, to evaluate a datum phase φ by solving two equations of three in the form I=cos (φ-δ), cos φ and cos (φ+δ).
Claim 10
Dependent Claim
139 words
Interferometric apparatus comprising: means for generating a first signal representing point-by-point variations in intensity I of a pattern of electromagnetic radiation resulting from an interference of first and second beams of such radiation derived from a coherent source, with at least the first beam being scattered from an object surface before interference with the second beam; means for changing the phase of one of said first and second beams by an amount δ other than an integer multiple of π to generate a second signal in like manner to said first signal; means for removing DC components from said first and second signals; and means, responsive only to said first and second signals following DC component removal, to evaluate a datum phase φ by solving two equations of three in the form I=cos (φ-δ), cos φ and cos (φ+δ).
Claim 11
Dependent Claim
18 words
Apparatus according to claim 8 comprising means for storing at least one of said first and second signals.
Claim 12
Dependent Claim
14 words
Apparatus according to claim 8 or 9 wherein said source is of laser form.
Claim 13
Dependent Claim
43 words
An apparatus as in claim 8, wherein said evaluating means evaluates equations representing said two signals, including ##EQU7## such that when δ is an odd multiple of π/2, φ=tan -1 ±I 1 /I 2 ; and solves said equation for said datum phase.
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) | 1994-09-16 | 1995-03-18 | 1995-09-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-09-16 | 1999-03-18 | 1999-09-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-09-16 | 2003-03-18 | 2003-09-17 | $7700.00 | Window Closed / Lapsed |