Compensation of refractivity perturbations in an interferometer path
First Claim
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1. A method, comprising:
- directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object;
directing a second measurement beam along a second path contacting the measurement object to determine a second interferometric phase related to the position of the measurement object;
determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase,wherein the contribution to the first interferometric phase due to perturbations in refractivity at a first time is related to a contribution to the second interferometric phase due to perturbations in refractivity at a second time different from the first time and a difference between the first time and the second time is related to a velocity of a gas in the first path; and
adjusting a relative position between the measurement object and another object based on the determined contribution.
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Abstract
In general, in one aspect, the invention features a method that includes directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object, directing a second measurement beam along a second path contacting the measurement object to determine an second interferometric phase related to the position of the measurement object, and determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase.
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Citations
64 Claims
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1. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, wherein the contribution to the first interferometric phase due to perturbations in refractivity at a first time is related to a contribution to the second interferometric phase due to perturbations in refractivity at a second time different from the first time and a difference between the first time and the second time is related to a velocity of a gas in the first path; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (2, 3, 4, 5, 6, 11, 15, 16, 17, 20, 22, 23, 38, 39, 40, 41, 42, 43, 46, 47, 52, 59)
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7. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine an a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity comprises determining a difference between the first interferometric phase and the second interferometric phase and correcting the difference between the first interferometric phase and the second interferometric phase for variations in an angular orientation of the measurement object; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (53, 60)
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8. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine an a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity comprises determining a difference between the first interferometric phase and the second interferometric phase and summing the differences of first and second interferometric phases determined for different times; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (9, 10, 54, 61)
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12. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine an a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, wherein determining the contribution to the first interferometric phase comprises determining a difference between the first interferometric phase and the second interferometric phase and determining a parameter related to the difference between the contribution to the first interferometric phase and a contribution to the second interferometric phase due to perturbations in refractivity based on the difference between the first interferometric phase and the second interferometric phase; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (13, 14, 55, 62)
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18. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine an a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity comprises determining a difference between the first interferometric phase and the second interferometric phase based on variations in the angular orientation of the measurement object and the variations in the angular orientation of the measurement object are measured using one or more interferometers direct respective measurement beams along measurement paths substantially non-orthogonal to a gas flow direction; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (19, 56)
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21. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object; directing a second measurement beam along a second path contacting the measurement object to determine an a second interferometric phase related to the position of the measurement object; and determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase and compensating the first interferometric phase for contributions due to non-perturbative variations in refractivity. - View Dependent Claims (57, 63)
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24. An apparatus, comprising:
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an interferometry system which during operation directs a first measurement beam along a first path contacting a measurement object, directs a second measurement beam along a second path contacting the measurement object, and directs a third measurement beam along a third path to contact a second measurement object; and an electronic controller which during operation determines a first and second interferometric phase related to a position of the measurement object based on the first and second measurement beams, respectively, determines a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase, determines a third phase related to a position of the second measurement object, and monitors variations in an angular orientation of the measurement object based on the third interferometric phase. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 44, 45, 48)
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49. A method, comprising:
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directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase at a first time related to a position of a measurement object at the first time; directing a second measurement beam along a second path contacting the measurement object to determine a second interferometric phase related to the position of the measurement object; determining a contribution to the first interferometric phase due to a perturbation in refractivity along the first path at the first time based on the second interferometric phase, wherein the first and second measurement beams have the same wavelength; and adjusting a relative position between the measurement object and another object based on the determined contribution. - View Dependent Claims (58, 64)
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50. An apparatus, comprising:
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a light source which during operation produces radiation at a first wavelength; an interferometry system which during operation receives radiation from the light source, directs a first measurement beam at the first wavelength along a first path contacting a measurement object, and directs a second measurement beam at the first wavelength along a second path contacting the measurement object; and an electronic controller which during operation determines a first and second interferometric phase related to a position of the measurement object based on the first and second measurement beams, respectively, and determines a contribution to the first interferometric phase at a first time due to a perturbation in refractivity along the first path at the first time based on the second interferometric phase.
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51. An apparatus, comprising:
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an interferometry system which during operation directs a first measurement beam along a first path contacting a measurement object and directs a second measurement beam along a second path contacting the measurement object; and an electronic controller which during operation determines a first and second interferometric phase related to a position of the measurement object based on the first and second measurement beams, respectively, and determines a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase and a velocity of the gas in the first path.
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Specification