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Author ORCID ID is 0000000256455173
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  1. In this study, a two-dimensional stitching interferometry system using two tiltmeters is proposed. During the scanning and the measurement, one tiltmeter stays with the interferometer and the other one is attached to the translation stage where the surface under test is placed. The differences of the x- and y-tilt readings between these two tiltmeters are recorded as the relative tilt between interferometer and surface under test. The relative tilt in both x- and y-directions are used to correct the surface tip/tilt of each subset, and then the piston is adjusted to get the final stitching surface map. As an example,more » a stitching result of a 125mm-long mirror surface is presented. The repeatability of our current stitching system is about 1.48 nm RMS. The stitching result is compared to the result of a one-dimensional angular-measurement-based stitching method to discuss the merits and limitation of the proposed method.« less
  2. Stereo phase unwrapping (SPU) has been increasingly applied to high-speed real-time fringe projection profilometry (FPP) because it can retrieve the absolute phase or matching points in a stereo FPP system without projecting or acquiring additional fringe patterns. Based on a pre-defined measurement volume, artificial maximum/minimum phase maps can be created solely using geometric constraints of the FPP system, permitting phase unwrapping on a pixel-by-pixel basis. However, when high-frequency fringes are used, the phase ambiguities will increase which makes SPU unreliable. Several auxiliary techniques have been proposed to enhance the robustness of SPU, but their flexibility still needs to be improved.more » In this paper, we proposed an adaptive depth constraint (ADC) approach for high-speed real-time 3D shape measurement, where the measurement depth volume for geometric constraints is adaptively updated according to the current reconstructed geometry. By utilizing the spatio-temporal correlation of moving objects under measurement, a customized and tighter depth constraint can be defined, which helps enhance the robustness of SPU over a large measurement volume. Besides, two complementary techniques, including simplified left-right consistency check and feedback mechanism based on valid area, are introduced to further increase the robustness and flexibility of the ADC. Furthermore, experimental results demonstrate the success of our proposed SPU approach in recovering absolute 3D geometries of both simple and complicated objects with only three phase-shifted fringe images.« less
  3. Recently we presented one-dimensional Angular-measurement-based Stitching Interferometry (ASI) technique for synchrotron mirror metrology coupling an autocollimator and a white light interferometer. In this work, we conduct a further study on the measurement repeatability of this technique under different conditions, e.g. different scanning time or lengths with/without system drift. The similarity between the angle measuring stitching technique in ASI and the slope integration technique in deflectometry is addressed. The analytic expression of the height repeatability is derived while the slope noise is a zero-mean uncorrelated additive noise. In addition, we use a set of typical stationary signals from the autocollimator andmore » the white light interferometer in a real experiment to simulate numerous virtual scans for the numerical calculation of the measurement repeatability under different measurement conditions. The simulation result predicts a link between the measurement repeatability and the scanning time with a constant speed. Moreover, it indicates that the major factor affecting the repeatability of our current ASI system is the system drift error.« less
  4. In this paper, we present one-dimensional stitching interferometry based on the angular measurement for high-precision mirror metrology. The tilt error introduced by the stage motion during the stitching process is measured by an extra angular measurement device. The local profile measured by the interferometer in a single field of view is corrected using the measured angle before the piston adjustment in the stitching process. Comparing to the classical software stitching technique, the angle measuring stitching technique is more reliable and accurate in profiling mirror surface at the nanometer level. Experimental results demonstrate the feasibility of the proposed stitching technique. Basedmore » on our measurements, the typical repeatability within 200 mm scanning range is 0.5 nm RMS or less.« less

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