US5139336A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Optical measuring apparatus using amplitude modulation of slipt beams
Assignee: BTG International Ltd
•
Filing: 1989-03-30
•
Granted: 1992-08-18
•
Expires: 2009-03-30
Abstract
Abstract PCT No. PCT/GB89/00325 Sec. 371 Date Sep. 14, 1990 Sec. 102(e) Date Sep. 14, 1990 PCT Filed Mar. 30, 1989 PCT Pub. No. WO89/09380 PCT Pub. Date Oct. 5, 1989.A heterodyne interferometer to achieve simultaneous and independent measurements of amplitude and phase includes a beam splitting device, BS which splits of the incident light beam into two parts with equal amplitudes and an angular deviation, alpha ; imposes two unequal frequency shifts F1 and F2 on the two beams and amplitude modulates the two beams in phase quadrature at frequency Fs. The two beams emerging from the beam splitter BS are focused by a lens L1 normally on to the surface of an object O. Upon reflection from the object surface, the two beams traverse through the lens and beam splitter a second time, where they are recombined. Both the frequencies and the amplitudes of the two beams will be shifted (or modulated) again after the second passage. The recombined beam is then diverted towards a photodetector PD via the beamsplitter.
Inventors
- 👤 Chung W. See
- 👤 Mehdi Vaez-Iravani
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 06:00
CPC Classifications
G; G01; G01B; G01B11/00; G01B11/30; G01B11/303; G01B11/02; G01B11/06; G01B11/0616; G01B11/0675; G01J; G01J9/00; G01J9/04
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
126 words
Optical apparatus for measuring topographical properties of a surface, comprising: means for splitting a beam of radiation into two component beams; means for focussing said two component beams onto a surface under test; means for recombining said two component beams after reflection from said surface to cause interference between said two component beams; and means for measuring a differential of at least one parameter of products of the interference of said two component beams, wherein said splitting means includes a beam splitting device which is adapted to split an incident light beam into two component beams with equal amplitudes and an angular deviation, to impose unequal frequency shifts and on the two component beams and amplitude modulate each of the two component beams in phase quadrature.
Claim 2
Dependent Claim
126 words
Optical apparatus for measuring topographical properties of a surface, comprising: means for splitting a beam of radiation into two component beams; means for focussing said two component beams onto a surface under test; means for recombining said two component beams after reflection from said surface to cause interference between said two component beams; and means for measuring a differential of at least one parameter of products of the interference of said two component beams, wherein said splitting means includes a beam splitting device which is adapted to split an incident light beam into two component beams with equal amplitudes and an angular deviation, to impose unequal frequency shifts and on the two component beams and amplitude modulate each of the two component beams in phase quadrature.
Claim 3
Dependent Claim
41 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 1, further comprising a lens, wherein the two component beams emerging from the beam splitter are focused by the lens normally onto the surface of an object.
Claim 4
Dependent Claim
83 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 2, wherein the lens is positioned in the system so that the point of apparent splitting is at the back focal point of the lens and the object is at its front focal plane to focus the two component beams normally onto an object so that upon reflection from the object surface, the two beams traverse through the lens and beam splitter a second time, where they are recombined.
Claim 5
Dependent Claim
42 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 3, further comprising a photodiode, wherein after reflection off the object and passage through the beam splitter interference between the two component beams is detected by the photodiode.
Claim 6
Dependent Claim
53 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 1 wherein said beam splitting device is a Bragg cell which amplitude modulates each of the two component beams in phase quadrature and said parameter is the phase or the amplitude, which is measured by a pair of detectors.
Claim 7
Dependent Claim
33 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 5 wherein the incoming beam of radiation is split into the first and zeroth order by said Bragg cell.
Claim 8
Dependent Claim
42 words
Optical apparatus for measuring the topographical properties of a surface as claimed in claim 5 wherein the Bragg cell is driven by two signals with frequencies close to its Bragg frequency and the sample is examined by the two first order beams.
References Cited (Backward Citations)
EP0011708A1
Cited
US4298283A
Cited
US4353650A
Cited
US4456339A
Cited
EP0108497A1
Cited
US4741620A
Cited
GB2146116A
Cited
US4650330A
Cited
US4577967A
Cited
GB2142427A
Cited
EP0167410A2
Cited
US4627730A
Cited
WO1988000683A1
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-08-18 | 1996-02-17 | 1996-08-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-08-18 | 2000-02-17 | 2000-08-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-08-18 | 2004-02-17 | 2004-08-18 | $7700.00 | Window Closed / Lapsed |