Patent ID: 7379187

Claim:
A detector for providing signals indicative of a phase difference between orthogonal, linearly polarized reference and object components of an interferometric measurement beam, comprising: at least a first beam splitting surface; at least first and second polarizers; and at least a first phase-shifting element, wherein the detector is configured such that: the first beam splitting surface is non-polarizing and is configured to receive the orthogonal, linearly polarized reference and object components as an input beam and to provide a first transmitted beam along a first transmitted beam path and a first reflected beam along a first transmitted beam path from the first beam splitting surface, the first beam splitting surface is configured such that when the orthogonal, linearly polarized reference and object components of the input beam are incident on the first beam splitting surface, polarization directions of the orthogonal, linearly polarized reference and object components form equal angles with a first plane of incidence defined by the input beam and a vector normal to the first beam splitting surface at a point of incidence of the input beam, such that reference and object components included in the first transmitted beam and the first reflected beam each include s-polarized components and p-polarized components defined with reference to the first plane of incidence, the first phase-shifting element is configured along one of the first transmitted beam path and the first reflected beam path to provide a phase-shift between the reference and object components in one of the first transmitted beam and the first reflected beam, and the first and second polarizers are arranged along the first reflected beam path and the first transmitted beam path, respectively, and configured to provide output signals such that: a first output signal derived from the first reflected beam is derived from interfering components of the reference and object components included in the first reflected beam that are nominally exclusively one of the p-polarized components and the s-polarized components defined with reference to the first plane of incidence; a second output signal derived from the first transmitted beam is derived from interfering components of the reference and object components included in the first transmitted beam that are nominally exclusively one of the p-polarized components and the s-polarized components defined with reference to the first plane of incidence; and a relationship between at least the first and second output signals is indicative of the phase difference between the orthogonal, linearly polarized reference and object components of the input beam.