Patent ID: 7796273
Filing Date: 2010-09-14
Classification: G01B

Abstract:
1. 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, each phase shift increment comprising a systematic component and a random component caused by the vibrations, the random component producing a probability that a phase shift increment will change sign relative to the sign for the systematic component, wherein the interferograms are recorded to produce at least two distinct sets of interferograms, the distinct sets comprising a first set comprising at least one pair of interferograms and a second set comprising at least one interferogram, wherein the probability of the sign change in the phase shift increment for the pair of interferograms in the first set is less than that for any pair of interferograms comprising at least one interferogram from the second set; calculating an initial phase map for the cavity based on at least the pair of interferograms in the first set of 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.