Patent ID: 6360012
Filing Date: 2002-03-19
Classification: G03F

Abstract:
An apparatus for measuring a wavefront of an optical system comprising:a reticle stage having a known first location; a reticle, placed on said reticle stage, said reticle having a plurality of gratings with different periods and orientations placed thereon; an optical system positioned to receive electromagnetic radiation passing through said reticle, said optical system having an optical axis and a nominal focus; an image stage having a known second location positioned to receive electromagnetic radiation passing through said optical system, said image stage movable in a direction substantially perpendicular to the optical axis and capable of moving a predetermined distance away from the nominal focus, whereby an image of the plurality of gratings with different periods and orientations is formed; a detector, for detecting the image of each of the plurality of gratings with different periods and orientations in at least two different planes; and a calculator coupled to said detector and said reticle and image stages, said calculator calculating wavefront information.