Patent ID: 6246481
Filing Date: 2001-06-12
Classification: G01B,G01N,G03F

Abstract:
An interferometry system comprising:an interferometer which during operation directs two beams along separate paths and then combines the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;a detector which responds to optical interference between the overlapping pair of exit beams and produces an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting .omega. between the two beams, if any, and a Doppler shift .phi. defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting .omega. and the Doppler shift .phi.; andan analyzer coupled to the detector which during operation: i) applies a window function to a sequence of values of the signal s(t); ii) Fourier transforms the windowed sequence of values, the Fourier transform defining a power spectrum equal to the square modulus of the Fourier transform; and iii) identifies at least one of the additional terms based on at least one peak in the power spectrum at a frequency not equal to the sum of the frequency splitting .omega. and the Doppler shift .phi..