MULTIPLE DEGREE OF FREEDOM INTERFEROMETER

摘要

An apparatus includes a multi-axis interferometer (114) for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams (122, 124, 126) each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom. Each output beam includes a beam component that contacts the measurement object at least one time along a common path (122) , and at least one of the beam components further contacts the measurement object at least a second time along a first path different from the common path.