Ranging beyond synthetic wavelengths with an undersampled spectral signal using tunable wavelength laser interferometry

Range extension achieved beyond the longest synthetic wavelength is possible by continuous tuning of the source wavelength and with the use of tilted interference for excess fraction extraction from a spectrally undersampled signal. This allows for the unique measurement of the extended range. For a correctly assumed fringe order for the initial source wavelength, the non-divergence of the estimated range as a function of wavelength tuning provides the potential range locations. These are further zeroed in by repeating the analysis by varying the tuning steps. A cascaded Michelson interferometer is used to uniquely measure the extended range as well as the spatial profile of the sample from a single set of wavelength scan. The excess fraction is accurately measured using the Fourier transform method of fringe analysis by virtue of tilted interference. With the support of sub-nanometer resolution in wavelength tuning, precise centimeter-scale ranging, along with micrometer-level profile resolution, is achieved.