Multiple-pass interferometry
First Claim
1. An apparatus comprising:
- a multiple-pass interferometer including reflectors to reflect at least two beams along multiple passes through the interferometer, the multiple passes including a first set of passes and a second set of passes, the reflectors having first alignments that are normal to the directions of the paths of the beams that are reflected by the reflectors, the two beams providing information about changes in a first location on one of the reflectors after the first set of passes, the two beams providing information about changes in the first location and changes in a second location on the reflector after the second set of passes, the paths of the beams being sheared during the first set of passes and during the second set of passes if at least one of the reflectors has an alignment other than the first alignment, and optics to redirect the beams after the first set of passes and before the second set of passes so that shear imparted during the second set of passes cancels shear imparted during the first set of passes.
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Accused Products
Abstract
Interferometry system including a multiple-pass interferometer having reflectors to reflect at least two beams along multiple passes through the interferometer. The multiple passes include a first set of passes and a second set of passes. The reflectors have first alignments that are normal to the directions of the paths of the beams that are reflected by the reflectors. The two beams provide information about changes in a first location on one of the reflectors after the first set of passes, and provide information about changes in the first location and changes in a second location on the reflector after the second set of passes. The paths of the beams are sheared during the first set of passes and during the second set of passes if at least one of the reflectors has an alignment other than the first alignment. The interferometry system includes optics to redirect the beams after the first set of passes and before the second set of passes so that shear imparted during the second set of passes cancels shear imparted during the first set of passes.
19 Citations
52 Claims
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1. An apparatus comprising:
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a multiple-pass interferometer including reflectors to reflect at least two beams along multiple passes through the interferometer, the multiple passes including a first set of passes and a second set of passes, the reflectors having first alignments that are normal to the directions of the paths of the beams that are reflected by the reflectors, the two beams providing information about changes in a first location on one of the reflectors after the first set of passes, the two beams providing information about changes in the first location and changes in a second location on the reflector after the second set of passes, the paths of the beams being sheared during the first set of passes and during the second set of passes if at least one of the reflectors has an alignment other than the first alignment, and optics to redirect the beams after the first set of passes and before the second set of passes so that shear imparted during the second set of passes cancels shear imparted during the first set of passes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A method comprising:
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directing a first measurement beam along a first set of passes through an interferometer to a first region on a measurement object;
directing a first reference beam along a first set of passes through the interferometer to a reference object;
combining the first measurement and reference beams to produce a first output beam after the first measurement and reference beams complete the first set of passes;
determining a change in position in the first region on the measurement object;
using optics to direct a portion of the first measurement beam to form a second measurement beam;
using the optics to direct a portion of the first reference beam to form a second reference beam;
directing the second measurement beam along a second set of passes through the interferometer to a second region on the measurement object;
directing the second reference beam along a second set of passes through the interferometer to the reference object;
combining the second measurement and reference beams to produce a second output beam after the second measurement and reference beams complete the second set of passes; and
determining a change in position in the second region on the measurement object;
wherein a rotation of the measurement object relative to the directions of the paths of the first and second measurement beams that are incident on the measurement object imparts beam shear to the first measurement beam during the first set of passes and to the second measurement beam during the second set of passes, and wherein the optics are configured to redirect the portion of the first measurement and reference output beams so that shear imparted upon the second measurement beam during the second set of passes cancels shear imparted upon the first measurement beam during the first set of passes. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42)
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43. An apparatus comprising:
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a multi-axis interferometer for measuring changes in position of a measurement object with respect to multiple degrees of freedom, the interferometer is configured to receive an input beam, direct a first-measurement beam derived from the input beam to make first and second passes to the measurement object about a first point on the measurement object, and then combine the first measurement beam with a first reference beam derived from the input beam to produce a first output beam comprising information about changes in distance to the first point on the measurement object, and the interferometer is further configured to direct a second-measurement beam derived from the input beam to make first and second passes to the measurement object about a second point on the measurement object, and then combine the second measurement beam with a second reference beam derived from the input beam to produce a second output beam comprising information about changes in distance to the second point on the measurement object, wherein the interferometer comprises fold optics positioned to reflect a portion of the first output beam an odd number of times in a plane defined by the incidence of the measurement beams on the measurement objects to define a secondary input beam, and wherein the second measurement beam and the second reference beam are derived from the secondary input beam. - View Dependent Claims (44, 45, 46, 47, 48, 49, 50, 51, 52)
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Specification