Patent ID: 7796275

Claim:
A phase-shifting interferometry 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, calculating an initial phase map for the cavity based on at least some of the recorded interferograms; calculating an estimate for each of at least some of the phase shift increments based on the initial phase map and at least some of the recorded interferograms; and calculating an improved phase map based on the calculated estimates for the phase shift increments and at least some of the recorded interferograms, wherein each phase shift increment comprises a systematic component and a random component caused by vibrations, and wherein calculating the phase shift increment estimates comprises determining a sign for the estimates based on information about the systematic components for at least some of the phase shift increments.