Abstract: An apparatus to measure the position of a mark, the apparatus including an objective lens to direct radiation on a mark using radiation supplied by an illumination arrangement; an optical arrangement to receive radiation diffracted and specularly reflected by the mark, wherein the optical arrangement is configured to provide a first image and a second image, the first image being formed by coherently adding specularly reflected radiation and positive diffraction order radiation and the second image being formed by coherently adding specularly reflected radiation and negative diffraction order radiation; and a detection arrangement to detect variation in an intensity of radiation of the first and second images and to calculate a position of the mark in a direction of measurement therefrom.

Abstract: An apparatus to measure the position of a mark, the apparatus including an objective lens to direct radiation on a mark using radiation supplied by an illumination arrangement; an optical arrangement to receive radiation diffracted and specularly reflected by the mark, wherein the optical arrangement is configured to provide a first image and a second image, the first image being formed by coherently adding specularly reflected radiation and positive diffraction order radiation and the second image being formed by coherently adding specularly reflected radiation and negative diffraction order radiation; and a detection arrangement to detect variation in an intensity of radiation of the first and second images and to calculate a position of the mark in a direction of measurement therefrom.

Abstract: An optical position measuring system (e.g., an interferometer) includes a superluminescent device (SLD) (e.g., a laser diode having at least one anti-reflective coated surface) and a detector. The SLD generates a light beam having a short coherence length (e.g., about 0.1 mm to about 0.5 mm, less than the optical path length of an optical element, and/or less than a spacing between optical elements). Through use of the short coherence length light beam, interference effects from spurious or ghost reflections that exist in conventional position measuring systems are substantially reduced or eliminated.

Abstract: An optical position measuring system (e.g., an interferometer) includes a superluminescent device (SLD) (e.g., a laser diode having at least one anti-reflective coated surface) and a detector. The SLD generates a light beam having a short coherence length (e.g., about 0.1 mm to about 0.5 mm, less than the optical path length of an optical element, and/or less than a spacing between optical elements). Through use of the short coherence length light beam, interference effects from spurious or ghost reflections that exist in conventional position measuring systems are substantially reduced or eliminated.