Patent ID: 7333214

Claim:
A method for providing signals indicative of a phase difference between orthogonal, linearly polarized, reference and object beam components that overlap in a combined interferometric measurement beam, the method comprising: providing a polarization-sensitive beam-deflecting element having orthogonal first and second polarization-sensitive axes, at least one polarizer, and at least one photodetector array; orienting the polarization-sensitive beam-deflecting element such that its first and second polarization-sensitive axes are respectively aligned parallel to the polarizations of the reference and object beams in the combined beam; inputting the reference and object beam components of the combined beam into the polarization-sensitive beam-deflecting element; outputting the reference and object beam components from the polarization-sensitive beam-deflecting element with a divergence angle between the beam components that is nominally a predetermined divergence angle, and such that the output reference and object beam components are partially overlapping; transmitting the partially overlapping reference and object beam components through a polarizer having a transmission axis that nominally bisects the angle between the polarizations of the reference and object beam components, such that the light transmitted by the polarizer forms an interference fringe pattern of nominally parallel fringes characterized by a constant fringe pitch that depends on a wavelength of the reference and object beam components and the divergence angle, and a variable spatial phase that depends on a phase difference between the reference and object beam components; and detecting changes in the spatial phase of the interference fringe pattern using a photodetector array that spatially filters the interference fringe pattern and outputs N signals having fixed phase shifts relative to one another, where N is an integer that is at least two, wherein a relationship including the values of the N signals is indicative of the phase difference between the reference and object beam components of the combined interferometric measurement beam.