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Optical interferometry

  • US 20030053079A1
  • Filed: 08/23/2002
  • Published: 03/20/2003
  • Est. Priority Date: 08/23/2001
  • Status: Active Grant
First Claim
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1. An apparatus comprising:

  • an interferometer to split an input beam into a measurement beam and at least one other beam, to direct the measurement beam along a measurement path that includes at least two passes to a measurement object, to direct the other beam along a reference path that includes at least two passes to a reference object, and to overlap the measurement beam with the other beam after the measurement beam completes the at least two passes, the path of the measurement beam being sheared during the first and second passes when the measurement object moves; and

    optics to redirect the measurement beam after the first pass and before the second pass so that the shear imparted during the second pass cancels the shear imparted during the first pass..

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