{
  "abstract": "The invention provides a method to determine an absolute position of an object using an interferometer system, comprising the steps of: providing a light beam; splitting the light beam in a measurement beam and a reference beam; guiding the measurement beam along a measurement path towards a reflective measurement surface on the object; guiding the reference beam along a reference path towards a reflective reference surface on a reference object; receiving the measurement beam after reflection on the reflective measurement surface and the reference beam after reflection on the reflective reference surface at a detector; measuring a phase signal based on the measurement beam and the reference beam received by the detector, separating a cyclic error phase component from the phase signal, determining the absolute position of the object on the basis of the cyclic error phase component.",
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  "title": "Method to determine an absolute position of an object, interferometer system, projection system and lithographic apparatus",
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