Patent ID: 7289222

Claim:
An interferometer apparatus comprising: a light source configured to emit a beam of measuring light; interferometer optics configured to direct the beam of measuring light toward an object, the interferometer optics comprising optical components symmetrically arranged with respect to a first optical axis; a detector system configured to detect an interference of a first portion of the beam of measuring light having interacted with the object and a second portion of the beam measuring light; wherein light in the beam of measuring light has at each location in a cross section of the beam, a radial component polarized in a direction radially oriented with respect to the first optical axis, and a tangential component polarized in a direction orthogonal to the radial component; wherein the interferometer optics comprises a polarization system including a polarization changing member positioned in the beam of measuring light, wherein the polarization changing member introduces a relative suppression of one of the radial component and the tangential component of light of the beam of measuring light with respect to the other component; and wherein an amount of the suppression of the one of the radial component and the tangential component gradually increases with increasing distance from the first optical axis.