---
publication_id: "OT-2026-000000579"
title: "Method to determine an absolute position of an object, interferometer system, projection system and lithographic apparatus"
published_at: "2026-09-15T19:03:06.598051Z"
canonical_url: "https://opentechnical.org/p/OT-2026-000000579"
categories:
  - "sensors-controls-machine-vision/position-and-presence-sensing"
keywords:
  - "g01b9/02078"
  - "g01b9/02015"
---

# Method to determine an absolute position of an object, interferometer system, projection system and lithographic apparatus

## 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.