Patent ID: 7948639

Claim:
A phase-shifting interferometry method for use in the presence of vibrations, the method comprising: recording an interferogram for each phase in a sequence of phases between test light reflected from a test surface and reference light reflected from a reference surface, the test and reference light being derived from a common source, each interferogram corresponding to an intensity pattern produced by interfering the reflected test light with the reflected reference light, the interferograms defining an interferometry signal for each of different transverse locations of a cavity defined by the test and reference surfaces, each interferometry signal comprising a series of intensity values corresponding to the sequence of phases, with the difference between each pair of phases in the sequence defining a corresponding phase shift increment, providing an initial phase map for the cavity and an initial estimate for AC and DC components for the recorded interferometry signals; calculating an estimate for each of at least some of the phase shift increments based on the initial phase map, the initial estimate for the AC and DC components, and at least some of the recorded interferograms; and calculating an improved phase map based on the calculated estimates for the phase shift increments, at least some of the recorded interferograms, and an improved estimate for the AC and DC components.