Patent ID: 7212291
Filing Date: 2007-05-01
Classification: G01B

Abstract:
1. An apparatus comprising: an interferometer positioned to derive measurement and reference wavefronts from a source of electromagnetic radiation, wherein the interferometer is configured to direct the measurement wavefront to reflect from a measurement surface and the reference wavefront to reflect from a reference surface, and further directs reflected measurement and reflected reference wavefronts to overlap with one another and to form an interference pattern; an auxiliary optic having a curved reflective surface positioned to redirect the measurement wavefront between the interferometer and the measurement surface; and a translation stage, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a zero optical path length difference between the measurement and reference wavefronts, and wherein the translation stage is configured to scan the optical measurement surface over the measurement surface.