White Light Interferometry (WLI) is a widely used technique for surface recovery. However, it is extremely sensitive to various external disturbances, increasing the uncertainty on measurement results. In this paper, a time-domain guided filtering-based surface recovery algorithm is proposed for WLI. The reference signal is firstly simulated according to the spectral map of illuminator employed in the system. The correlation between the actual correlogram and the simulated one is then analyzed through the generalized cubic correlation delay estimation method. The corrected correlogram is obtained as a local linear transformation of the reference one that has been shifted, where the linear coefficients are estimated using least squares analysis. The surface height is then retrieved based on mapping relationship between the phase and frequency. The capability of the proposed method on noise suppression is investigated through simulation under different levels of additive noise. In the experiment, a step height standard (VLSI,181.0nm±2.1nm) is employed, which verifies the performance of the proposed method on measurement accuracy and reliability.
White light interferometry (WLI) provides noncontact, high-precision surface profiling and inspection for ultra-precision machining. This paper presented a signal time-domain mode-decomposition denoising based surface recovery algorithm for WLI. In this work, the captured correlogram is firstly decomposed into a series of modes with different central spectrums by means of the variation mode-decomposition (VMD), and the spectral component of each intrinsic mode can be derived through the Fourier transform. Afterwards, the noise existed in each spectral component is eliminated through windowed Fourier filtering (WFF), where the filtering threshold is decided by the ratio of spectral energy of intrinsic mode comparing with that of the correlogram. The denoised correlogram could then be extracted as the sum of filtered intrinsic modes. And the surface height isfinally retrieved through envelope peak location by applying Hilbert transform. The effectiveness of the proposed method on noise suppression is investigated under different levels of additive noises occurred on simulated correlograms. Moreover, a height step standard with calibrated values 1.762±0.010μm is further testified, where the measurement accuracy of the proposed method is totally verified.
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