Interferometric optical systems having simultaneously scanned optical path length and focus
AssigneeZygo Corporation
InventorsPeter J. De Groot, Xavier Colonna De Lega, Senthil Balasubramaniam
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Abstract
In certain aspects, the invention features scanning interferometry systems and methods that can scan an optical measurement surface over distances greater than a depth of focus of imaging optics in the interferometry system, while keeping an optical measurement surface in focus (i.e., maintaining an image of the optical measurement surface coincident with the detector). The optical measurement surface refers to a theoretical test surface in the path of test light in the interferometer that would reflect the test light to produce an optical path length difference (OPD) between it and reference light that is equal to a constant across a detector.
Claims49
A method comprising:
- imaging test light reflected from a test surface to interfere with reference light on a camera and form an interference pattern, the test light and reference light being derived from a common source,
- wherein optical paths for the test and reference light define an optical measurement surface corresponding to a theoretical test surface that would reflect the test light to produce a constant optical path length difference between it and the reference light over the camera;
- scanning the optical measurement surface relative to the test surface, wherein the scanning comprises scanning a radius of curvature of a locally spherical portion of the optical measurement surface;
- and
- adjusting a position of the camera relative to an image of the optical measurement surface nearest the camera during the scan of the optical measurement surface.
Apparatus comprising:
- an interferometric imaging system configured to image test light reflected from a test surface to interfere with reference light on a camera and form an interference pattern, the test light and reference light being derived from a common source,
- wherein optical paths for the test and reference light define an optical measurement surface corresponding to a theoretical test surface that would reflect the test light to produce a constant optical path length difference between it and the reference light over the camera;
- wherein the interferometric imaging system comprises a first stage configured to scan the optical measurement surface relative to the test surface by scanning a radius of curvature of a locally spherical portion of the optical measurement surface, and a second stage configured to adjust a position of the camera relative to an image of the optical measurement surface nearest the camera during the scan of the optical measurement surface.
An apparatus comprising:
- an interferometric imaging system configured to image test light reflected from a test surface to interfere with reference light reflected from a reference surface on a camera and form an interference pattern, the test light and reference light being derived from a common source, the interferometric imaging system comprising:
- measurement optics configured to shape the test light so that the test light diverges at the test surface;
- a first stage configured to translate the reference surface relative to the measurement optics to vary an optical path difference between the test light and reference light at the camera, and
- a second stage configured to adjust a position of the camera relative to the measurement optics simultaneously with the motion of the first stage.
A method comprising:
- imaging test light reflected from a test surface to interfere with reference light on a camera and form an interference pattern, the test light and reference light being derived from a common source,
- wherein optical paths for the test and reference light define an optical measurement surface corresponding to a theoretical test surface that would reflect the test light to produce a constant optical path length difference between it and the reference light over the camera;
- scanning the optical measurement surface relative to the test surface, wherein the test surface is stationary relative to the light source during the scan of the optical measurement surface;
- and
- adjusting a position of the camera relative to an image of the optical measurement surface nearest the camera during the scan of the optical measurement surface.
Dependencies are inferred from the claim text.