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Phase Measuring Deflectometry (PMD) with high dynamic range and high robustness is a more powerful method to achieve the integration of optical components fabrication and testing, which would avoid the secondary positioning error caused by the removal of optical components in off-line status. However, for surface shape measurement of transparent element, the captured fringe patterns are superposition of the patterns reflected from the front and rear surfaces, leading to the failure of the traditional phase-shifting algorithm to extract the true phase distribution. In order to separate the superposed fringe patterns, the limitations of the existing methods such as UV deflectometry and polarized light deflectometry, which require special light source and polarizer filter, are expensive instrument and complex processes. Moreover, only the front surface shape can be reconstructed at a time, which lowers the efficiency of the measurement. To achieve in-situ measurement of the front and rear surface shapes of the transparent element simultaneously, the combination of PMD and power spectrum estimation is used to separate parasitic fringe patterns. And the front and rear surface shapes are reconstructed using ray tracing and non-linear optimization. The feasibility of the proposed method is demonstrated by numerical simulation. In the experiment, the transparent element with a thickness of about 10 mm is detected and the front and rear surface shapes are reconstructed. The front and rear surface shapes differences of the transparent element with a diameter of 77.8 mm are 173 nm in RMS and 212 nm in RMS, respectively.
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