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US4834111A
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Heterodyne interferometer
Assignee: Columbia University
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Filing: 1987-01-12
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Granted: 1989-05-30
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Expires: 2007-01-12
Abstract
Abstract This invention concerns a heterodyne interferometer for measuring the amplitude of vibration of a vibrating object. The invention is particularly useful for measuring the amplitude of vibrations of objects having reflectivities below about 0.02% or for measuring vibrations amplitudes below about 10-17 cm. The invention comprises a laser and a beam splitter for producing an object light wave and a reference light wave; at least one modulator for changing the frequencies of the object light wave and the reference light wave thereby producing a predetermined offset; means for directing the object light wave onto the vibrating object; and a photodetector for producing, at a frequency equal to the predetrmined offset, a beat signal which varies according to variations in the interference resulting from combining the reflected object light wave and the reference light wave.
Inventors
- 👤 S. M. Khanna
- 👤 J. F. Willemin
- 👤 R. Dandliker
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 14:13
CPC Classifications
A; A61; A61B; A61B5/00; A61B5/103; A61B5/11; A61B5/1126; G; G01; G01H; G01H9/00
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
274 words
A heterodyne interferometer for measuring the amplitude of vibration of a vibrating object which comprises: (a) a laser for emitting a monochromatic light wave; (b) a beam splitter for splitting the light wave into an object light wave and a reference light wave, each having the same frequency; (c) a modulator for changing the frequency of the object light wave and the reference light wave so as to produce a predetermined offset between the frequency of the object light wave and the frequency of the reference light wave, said modulator being so positioned with respect to the beam splitter that the object light wave and the reference light wave pass through the modulator thereby changing their frequencies; (d) means for directing the object light wave onto the vibrating object, said means so positioned between the object and the modulator that at least a portion of the object light wave is directed onto and reflected off of the object; (e) a photodetector for producing, at a frequency equal to the predetermined offset, a beat signal varying in accordance with variations in the interference resulting from combining at least a portion of the reflected object light wave and the reference light wave wherein the power of the reference light wave is greater than the power of the portion of the reflected object light wave, the photodetector being so positioned with respect to the object and the beam splitter that it detects and measures the interference; and (f) means for processing the beat signal to measure variations in its phase or amplitude, said means being electrically connected to the photodetector in order to receive the beat signal.
Claim 2
Dependent Claim
274 words
A heterodyne interferometer for measuring the amplitude of vibration of a vibrating object which comprises: (a) a laser for emitting a monochromatic light wave; (b) a beam splitter for splitting the light wave into an object light wave and a reference light wave, each having the same frequency; (c) a modulator for changing the frequency of the object light wave and the reference light wave so as to produce a predetermined offset between the frequency of the object light wave and the frequency of the reference light wave, said modulator being so positioned with respect to the beam splitter that the object light wave and the reference light wave pass through the modulator thereby changing their frequencies; (d) means for directing the object light wave onto the vibrating object, said means so positioned between the object and the modulator that at least a portion of the object light wave is directed onto and reflected off of the object; (e) a photodetector for producing, at a frequency equal to the predetermined offset, a beat signal varying in accordance with variations in the interference resulting from combining at least a portion of the reflected object light wave and the reference light wave wherein the power of the reference light wave is greater than the power of the portion of the reflected object light wave, the photodetector being so positioned with respect to the object and the beam splitter that it detects and measures the interference; and (f) means for processing the beat signal to measure variations in its phase or amplitude, said means being electrically connected to the photodetector in order to receive the beat signal.
Claim 3
Dependent Claim
26 words
The interferometer of claim 1, wherein the modulator comprises a first modulator on the object light wave and a second modulator on the reference light wave.
Claim 4
Dependent Claim
18 words
An interferometer of claim 2, wherein the first modulator and the second modulator each comprises an acousto-optical modulator.
Claim 5
Dependent Claim
20 words
An interferometer of claim 3, wherein the two modulators are driven by predetermined frequencies which differ by the predetermined offset.
Claim 6
Dependent Claim
12 words
An interferometer of claim 1, wherein the modulator comprises an acousto-optical modulator.
Claim 7
Dependent Claim
21 words
An interferometer of claim 1, wherein the means of directing the object light wave onto the object comprises an optical instrument.
Claim 8
Dependent Claim
13 words
An interferometer of claim 1, wherein the photodetector comprises a PN junction photodiode.
Claim 9
Dependent Claim
12 words
An interferometer of claim 7, wherein the photodiode is a silicon photodiode.
Claim 10
Dependent Claim
12 words
An interferometer of claim 1, wherein the photodetector comprises a photomultiplier tube.
Claim 11
Dependent Claim
12 words
An interferometer of claim 1, wherein the photodetector comprises a photoconductive device.
Claim 12
Dependent Claim
18 words
An interferometer of claim 1, wherein the means of processing the beat signal comprises a phase tracking system.
Claim 13
Dependent Claim
17 words
An interferometer of claim 1, wherein the means of processing the beat signal comprises a frequency demodulator.
Claim 14
Dependent Claim
11 words
An interferometer of claim 12, wherein the demodulator is an FM-demodulator.
Claim 15
Dependent Claim
11 words
An interferometer of claim 13, wherein the FM-demodulator comprises an FM-receiver.
References Cited (Backward Citations)
US4208128A
Cited
US4172382A
Cited
US4422764A
Cited
US4681447A
Cited
US4554836A
Cited
US4643575A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-05-29 | 1992-11-28 | 1993-05-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-05-29 | 1996-11-28 | 1997-05-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-05-29 | 2000-11-28 | 2001-05-30 | $7700.00 | Window Closed / Lapsed |