Absolute distance measurement with synchronously sampled white-light channelled spectrum interferometry

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Abstract
We describe a white-light channelled spectrum interferometer for absolute distance measurement in the range of 8 mu m to 1.9 mm, using a diffractive element and a linear detector array to scan the interference signal. The local phase of the spectral fringe pattern is obtained from synchronized sampling with four samples per fringe period. The absolute distance is calculated from the slope of the measured phases against wavelength. First, the distance is determined to better than lambda /8 in order to overcome the phase ambiguity. Then, one of the measured local phases can be used to determine the exact distance with interferometric accuracy. Test results showed an accuracy of better than 2 nm for a distance of 125 mu m and better than 12 nm for any position within 50 mu m to 150 mu m.
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