EP0194941A2
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Heterodyne interferometer system
Assignee: Zygo Corp
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Filing: 1986-03-11
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Granted: —
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Expires: 2006-03-11
Abstract
Abstract A heterodyne interferometer system utilizes a single stabilized frequency linearly polarized laser input beam (18) from a light source (10) which is provided to an acousto-optic device (20) along with a frequency stabilized electrical reference signal (32) from an oscillator (30) for transforming the input beam (18) into a pair of orthogonally polarized beams (40,50) differing in frequency by the reference signal frequency prior to providing these beams (40,50) to a polarization type interferometer (70). A mixing polarizer (60) mixes the beams (46,56) after they traverse the interferometer (70) and provides the mixed beams (62,64) to a photoelectric detector (65) where they are utilized to produce an electrical measurement signal (66). This electrical measurement signal (66) is processed in a phase meter/accumulator (68) along with the reference signal (32) to produce an output signal (80) which is the sum of phase difference on a cycle-by-cycle basis between the measurement signal (66) and the reference signal (32). The phase meter/accumulator (68) includes an analog-to-digital converter and a memory register for the previous cycle, with the measurement resolution being determined by the number of bits of the analog-to-digital converter.
Inventors
- 👤 Gary E. Sommargren
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 05:48
CPC Classifications
G; G01; G01B; G01B9/00; G01B9/02; G01B9/02041; G01B9/02045; G01B9/02001; G01B9/02002; G01B9/02083; G01J; G01J9/00; G01J9/04; G01B2290/00; G01B2290/70
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
228 words
A heterodyne interferometer system comprising: a light source (10) for providing a linearly polarized stabilized single frequency optical input beam (18) having a first frequency; means (30) for providing a frequency stabilized reference electrical signal (32) having a second frequency; acousto-optical means (20) coupled to said input beam providing means and said reference signal providing means for transforming said input beam into a pair of orthogonally polarized beams (40,50) having associated optical frequencies which differ in frequency from each other by said reference signal second frequency; means (70) coupled to said acousto-optical means and having a fixed length optical path traversed by one of said pair of orthogonally polarized beams and a variable length optical path traversed by said other one of said pair of orthogonally polarized beams for providing interferometric output beams (46,56); means (60) coupled to said interferometric output beam providing means for mixing said interferometric output beams; means (65)coupled to said mixing means for providing an electrical measurement signal (66) from said mixed interferometric output beams; and means (68) coupled to said measurement signal providing means and said reference signal providing means for providing an output signal (80) based on a difference in phase between said reference signal and said measurement signal, said phase difference being based on a change in length of said variable length optical path in said interferometric output beam providing means.
Claim 2
Dependent Claim
228 words
A heterodyne interferometer system comprising: a light source (10) for providing a linearly polarized stabilized single frequency optical input beam (18) having a first frequency; means (30) for providing a frequency stabilized reference electrical signal (32) having a second frequency; acousto-optical means (20) coupled to said input beam providing means and said reference signal providing means for transforming said input beam into a pair of orthogonally polarized beams (40,50) having associated optical frequencies which differ in frequency from each other by said reference signal second frequency; means (70) coupled to said acousto-optical means and having a fixed length optical path traversed by one of said pair of orthogonally polarized beams and a variable length optical path traversed by said other one of said pair of orthogonally polarized beams for providing interferometric output beams (46,56); means (60) coupled to said interferometric output beam providing means for mixing said interferometric output beams; means (65)coupled to said mixing means for providing an electrical measurement signal (66) from said mixed interferometric output beams; and means (68) coupled to said measurement signal providing means and said reference signal providing means for providing an output signal (80) based on a difference in phase between said reference signal and said measurement signal, said phase difference being based on a change in length of said variable length optical path in said interferometric output beam providing means.
Claim 3
Dependent Claim
42 words
A heterodyne interferometer system in accordance with Claim 1, wherein said interferometric output beam providing means comprises a polarization type interferometer (70), said polarization type interferometer comprising a pair of orthogonally disposed retroreflectors (74,76) and a polarization beamsplitter (72) optically aligned therewith.
Claim 4
Dependent Claim
57 words
A heterodyne interferometer system in accordance with claim 2, wherein one (74) of said pair of retroreflectors is fixed relative to said polarization beamsplitter (72) and the other (76) of said pair of retroreflectors is movable relative to said polarization beamsplitter in a direction parallel with said transmitted beam of said orthogonally polarized pair of beams (40,50).
Claim 5
Dependent Claim
87 words
A heterodyne interferometer system in accordance with Claim 3, wherein said electrical measurement signal (66) has a frequency f defined by the expression: where f 0 is the frequency of said reference signal; v is the velocity of said movable retroreflector (76), being positive when the movement is toward said beamsplitter (72) and negative when the movement is away from said beamsplitter; and X is the wavelength of a measurement beam derived from the transmitting of one of said pair of orthogonally polarized beams by said beamsplitter.
Claim 6
Dependent Claim
46 words
A heterodyne interferometer system in accordance with claim 4, wherein said phase meter/accumulator means (68) comprises means for integrating the frequency difference between said measurement signal and said reference signal for providing said output signal (80) which is proportional to the displacement of said movable retroreflector.
Claim 7
Dependent Claim
32 words
A heterodyne interferometer system in accordance with claim 5, wherein said integrating means comprises means for adding the phase differences between said measurement signal and said reference signal on a cycle-by-cycle basis.
Claim 8
Dependent Claim
53 words
A heterodyne interferometer system in accordance with Claim 6, wherein said cycle-by-cycle phase difference adding means comprises analog-to-digital conversion means (83) connected to said measurement signal providing means and said reference signal providing means for providing a digital output signal (84) proportional to the phase of said reference signal at the sampling instant.
Claim 9
Dependent Claim
41 words
A heterodyne interferometer system in accordance with claim 7, wherein said phase difference adding means further comprises a memory register (92) connected to said analog-to-digital conversion means output for storing the corresponding previous cycle output of said analog-to-digital conversion means (83).
Claim 10
Dependent Claim
84 words
A heterodyne interferometer system in accordance with Claim 8, wherein said phase difference adding means further comprises a phase difference calculator means (86) connected to said analog-to-digital conversion means (83) output and said memory register (92) for providing a phase difference output signal (87) derived from said digital output signal and said corresponding previous cycle output stored in said memory register, said phase difference output signal being the measure of phase difference between said reference signal and said measurement signal at each sampling instant.
Claim 11
Dependent Claim
116 words
A heterodyne interferometer system in accordance with Claim 9, wherein said phase difference adding means further comprises accumulator means (88) connected to said phase difference calculator means (86) for adding the phase differences calculated at each cycle of said measurement signal, said output signal (80) from said accumulator means being the sum of said phase differences and being proportional to the displacement of said movable retroreflector (76), the measured displacement d of said movable retroreflector being defined by the expression where N is the output of said accumulator means; X is the wavemength of said measurement beam; m is the number of bits of said analog-to-digital conversion means; and is the measurement resolution of said system.
References Cited (Backward Citations)
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