Abstract
Absolute distance measurement is necessary for many applications where the distance to a fixed-target is required. In this paper, frequency scanning interferometry is implemented with an external cavity tunable diode laser, which has a wavelength scanning range of (665-675 nm), to measure distances up to 5 m absolutely (achieved by multi-reflection system). An ultra-low expansion (ULE) Fabry-Perot (FP) cavity has been used as a reference to measure the tunable-laser scanning range. Absolute distance is determined by counting the synthetic fringes and FP peaks simultaneously while scanning the laser frequency. A fringe processing technique is developed to perform online distance measurement even though the tunable laser is not mode-hop free. This fringe processing method enables simple, fast and accurate distance measurements with repeatability ±3.9×10-6 L and combined uncertainty ±38.9×10-6 L which is limited by the calibration system used.
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