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

摘要

Methods and systems for measuring asymmetric surface topology are described. In one aspect, a method includes directing a test beam including a spherical wave front along an optical axis to reflect from a test surface; combining the test beam reflected from the test surface with a reference beam to form an interferogram on a detector, where the test and reference beams are derived from a common source; and recording the interferogram for each of multiple lateral displacements of the test surface relative to the optical axis. For each recorded interferogram, the curvature of the spherical wave front at the test surface substantially matches a local curvature of the test surface along a first axis orthogonal to the optical axis, and the multiple lateral displacements of the test surface each include a component along a second axis orthogonal to each of the first axis and the optical axis.