Patent ID: 7019843

Claim:
Interferometric apparatus comprising: a translation stage; an electro-mechanical arrangement for selectively translating said translation stage in at least one of at least two orthogonal directions; at least one mirror mounted in a predetermined manner with respect to said translation stage, said at least one mirror having a reflecting surface; interferometer means for generating a plurality of measurement beams adapted and arranged for projection onto said reflecting surface to measure the displacement of said translation stage in at least one direction and at least a local slope of said at least one mirror; control means having a mode of operation for selectively translating said translation stage, said at least one mirror and said interferometer means relative to one another in said mode of operation so that selected ones of said plurality of beams of said interferometer means scan said at least one mirror along at least one corresponding datum line to generate at least one signal comprising information indicative of the local slope of said reflecting surface along said at least one corresponding datum line in at least one plane with a surface normal orthogonal to the direction of scan; and signal and analysis means for extracting said information contained in said at least one signal and determining the local shape of said at least one mirror.