Patent ID: 8531677

Claim:
A method of measuring a test object with a frequency-shifting interferometer comprising steps of varying a frequency of a measuring beam with a tunable light source of the frequency-shifting interferometer over a range of beam frequencies, forming with the frequency-shifting interferometer progressively changing interference images of the test object with the measuring beam over the range of beam frequencies, recording a set of interference image data corresponding to a succession of the changing interference images of the test object as the measuring beam is varied in frequency over the range of beam frequencies, monitoring the beam frequencies at which the interference image data corresponding to the succession of interference images are recorded, identifying a subset within the set of recorded interference data corresponding to interference images formed by beam frequencies that exhibit a predetermined pattern of beam frequency spacing and excluding from the subset other of recorded interference data corresponding to other of the succession of changing interference images formed by beam frequencies that that do not exhibit the predetermined pattern of beam frequency spacing, and processing the subset of recorded interference data without processing the recorded interference data excluded from the subset for deriving measurements for producing an optical profile of the test object.