A moire-effect-based procedure used to measure the wavelength of coherent sources is shown. Two plane waves, individually coherent but mutually incoherent and located at the entrance pupil of a Michelson interferometer with slightly tilted mirrors, generate a moire pattern at the output plane. The spatial period of that moire pattern is determined by the spatial frequencies of the interferograms superimposed on intensity. Thus the spatial frequency of such moire patterns allows the establishment of a ratio between the wavelengths of the sources that illuminate the interferometer. This ratio can be applied for the accurate determination of determining an unknown wavelength in terms of a reference wavelength, as we show both theoretically and experimentally.
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