In this investigation, we propose a dual low coherence scanning interferometer as the novel concept to measure large height steps on the topographic surface of a specimen and the thickness profile of a transparent optical plate. Dual low coherence characteristics by the tandem interferometric configuration can generate several discrete correlograms for the measured surfaces, which provide the possibility to reduce the scanning length of typical low coherence scanning interferometry significantly. Also, the spectrally-resolved interferometric method is combined to monitor the distance gaps between correlograms caused by the dual low coherence. To verify the proposed interferometry, a large height step specimen and a silicon wafer were used and the 3D surface and thickness profiles were rapidly and successfully measured. In addition, the technique which can identify each correlogram by the insertion of dispersive plates are suggested in this paper.
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