Patent ID: 6856402

Claim:
An interferometry system comprising: a first polarizing beam splitter positioned to separate an input beam into a first beam and a second beam; a beam steering element positioned to direct the first beam, and not the second beam, the first beam contacting the beam steering element; an interferometer positioned to receive one of the first and second beams and direct it to a measurement object, which reflects it to define a measurement return beam, and wherein the interferometer is further positioned to receive the other of the first and second beams and direct it to a reference object, which reflects it to define a reference return beam; and an electronic control circuit coupled to the beam steering element, wherein during operation the control circuit adjusts the orientation of the beam steering element in response to changes in the angular orientation of the measurement object, wherein the beam steering element is further positioned to direct the return beam derived from the second beam, and not the return beam derived from the first beam, the return beam derived from the second beam contacting the beam steering element, and wherein the first polarizing beam splitter is positioned to recombine the return beams to form an output beam.