Interferometer and method for measuring non-rotationally symmetric surface topography having unequal curvatures in two perpendicular principal meridians

An interferometry system for characterizing a test surface, the system comprising:

• (a) a detector;
• (b) an interferometer coupled to the detector, the interferometer comprising a mount to adjustably position the test surface, the interferometer being configured to
• (1) direct a test beam comprising a spherical wave front along an optical axis to reflect from the test surface, and
• (2) combine the reflected test beam with a reference beam to form an interferogram on the detector, wherein the test and reference beams are derived from a common source;
• and
• (c) an electronic processor coupled to the detector and the interferometer, the electronic processor being programmed to
• (1) determine a first axis of the test surface based on the interferogram formed on the detector when a curvature of the spherical wave front at the test surface substantially matches a local curvature of the test surface along the determined first axis,
• (2) instruct the mount to displace the test surface relative to the optical axis such that each of multiple displacements of the test surface comprises a component along a second axis orthogonal to each of the optical axis and the determined first axis, wherein a local curvature of the test surface along the second axis is different from the local curvature of the test surface along the determined first axis, and the test surface is non-rotationally symmetric,
• (3) record the interferogram for each of the multiple lateral displacements of the test surface, and
• (4) reconstruct the test surface based on the interferograms recorded in (3) to obtain a three-dimensional test surface that is non-rotationally symmetric.

An interferometry method for characterizing an atoric test surface, the method comprising:

• (a) directing a test beam comprising a spherical wave front along an optical axis to reflect from the atoric test surface;
• (b) combining the test beam reflected from the atoric test surface with a reference beam to form an interferogram on a detector, wherein the test and reference beams are derived from a common source;
• and
• (c) recording the interferogram for each of multiple lateral displacements of the atoric test surface relative to the optical axis, wherein the atoric test surface is non-rotationally symmetric.

An interferometry method for characterizing a toric test surface, the method comprising:

• (a) directing a test beam comprising a spherical wave front along an optical axis to reflect from the toric test surface;
• (b) combining the test beam reflected from the toric test surface with a reference beam to form an interferogram on a detector, wherein the test and reference beams are derived from a common source;
• and
• (c) recording the interferogram for each of multiple lateral displacements of the toric test surface relative to the optical axis, wherein the toric test surface is non-rotationally symmetric.