26 June 2017 A novel white-light interferometry using low differential-frequency heterodyne system
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The optical surface profiler offers fast non-contact and high-precision 3D metrology for complex surface features, which are widely used in the field of precision machining manufacturing. The optical surface profiler traditionally adopts the white light interference (WLI) technique which mainly includes optical interference system and high-precision displacement stage. The accuracy of the displacement table determines the longitudinal resolution of the instrument. In this paper, a novel WLI technique is proposed, i.e. full-field heterodyne WLI, which combines common displacement stage, low differential-frequency heterodyne system and optical interferometry system. The low differential-frequency heterodyne system generates heterodyne signal in the range of laser coherence length. By using the digital phase shift in substitution for the mechanical phase shift, the vertical resolution increases from the sub-nanometer level to the sub-angstrom level. Due to the low difference frequency technique, the common area array detector acquisition is available. A fixed displacement stage position obtains a set of three-dimensional data cubes. Through Fourier-Transform process of the time series data, the initial phase of each pixel at a specific heterodyne frequency is calculated and transformed into surface height information. By using phase unwrapping, the object surface profile can be restored within the laser coherence length. Through digital phase-shifting, phase extraction technology replaces the intensity extraction technology, the moving distance of the displacement can be calibrated with high precision. Thus it can achieve a large range of high-precision contour measurement and reduce the cost of the instrument.
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Xinxin Kong, Xinxin Kong, Bin Xiangli, Bin Xiangli, Wenxi Zhang, Wenxi Zhang, Zhou Wu, Zhou Wu, Yang Li, Yang Li, Xiaoyu Lv, Xiaoyu Lv, } "A novel white-light interferometry using low differential-frequency heterodyne system", Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 103292E (26 June 2017); doi: 10.1117/12.2270140; https://doi.org/10.1117/12.2270140


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