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Cyclic error compensation in interferometry systems

  • US 7,616,322 B2
  • Filed: 08/03/2006
  • Issued: 11/10/2009
  • Est. Priority Date: 07/08/2002
  • Status: Active Grant
First Claim
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1. A method comprising:

  • providing an interference signal S(t) from interference between two beams directed along different paths, wherein the signal S(t) is indicative of changes in an optical path difference n{tilde over (L)}(t) between the different paths, where n is an average refractive index along the different paths, {tilde over (L)}(t) is a total physical path difference between the different paths, and t is time; and

    providing an error signal to reduce errors in an estimate of {tilde over (L)}(t), the error signal being derived at least in part based on one or more collective properties of a distribution of multi-dimensional values, at least one of the multi-dimensional values in the distribution being generated from a plurality of samples of the signal S(t);

    wherein one of the paths is associated with a position of a reference object and the other path is associated with a position of a moveable measurement object;

    wherein the position of the moveable object is controlled by a servo system having a bandwidth and fS, the samples of the signal S(t) from which the multi-dimensional values are calculated correspond to sample times at which the velocity v of the moveable measurement object relative to the reference object divided by a wavelength λ

    of the beams is less than ten times the bandwidth fS; and

    wherein the servo system controls the position of the measurement object based on the signal S(t) and the error signal.

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