RESUMEN
A channeled spectropolarimeter is a powerful tool for the simultaneous measurement of the intensity, spectral, and polarization information of a target. However, the fore-optics introduce additional polarization information, which leads to inaccurate reconstruction of the Stokes parameters. In this study, we propose a simple method for polarimetric calibration and Stokes parameters reconstruction for a fieldable channeled spectropolarimeter. The polarization effects of the fore-optics and phase factors of the high-order retarders at varying view angles are considered and calibrated independently using a single reference beam. Moreover, the misalignment of the retarders is also considered. Simulation results demonstrate that the polarization effects of fore-optics can be precisely determined, enhancing the measurement accuracy of the Stokes parameters by approximately an order of magnitude. The effectiveness of the proposed method is also verified experimentally.
RESUMEN
This Letter introduces sub-Nyquist sampling vertical scanning white light interferometry (SWLI) using deep learning. The method designs Envelope-Deep Residual Shrinkage Networks with channel-wise thresholds (E-DRSN-cw), a network model extracting oversampling envelopes from undersampled signals. The model improves the training efficiency, accuracy, and robustness by following the soft thresholding nonlinear layer approach, pre-padding undersampled interference signals with zeros, using LayerNorm for augmenting inputs and labels, and predicting regression envelopes. Simulation data train the network, and experiments demonstrate its superior performance over classical methods in the accuracy and the robustness. The E-DRSN-cw provides a swift measurement solution for SWLI, removing the need for prior knowledge.
RESUMEN
White light scanning interferometry is a commonly used optical measurement method for three-dimensional (3D) surface profiles. In the case of large phase errors, accurate height values can generally be obtained indirectly from the interferometric signal envelope information derived using various envelope extraction methods. However, the current envelope extraction algorithms have the disadvantages of low robustness, increasing the half-width of the envelope information, and requiring correct parameter settings in advance. In this study, the pseudo Wigner-Ville distribution is modified and applied to white light scanning interferometric 3D measurement to avoid the above-mentioned drawbacks. Simulations and experiments are performed in a single-frequency mode (only the approximate central wave-number is used to guide both the proposed and wavelet transform methods). The simulation results prove that the proposed method has a 31.7% higher reconstruction accuracy than the wavelet transform method under a 25â dB signal to noise ratio condition. Concurrently, the proposed method is insensitive to the change in the central wavelength with a constant central wave-number parameter and has a good extraction effect for a long coherent length. The experiments measure standard step objects (VLSI standard, 1.761 ± 0.01â µm), and the reconstruction height error of the proposed method is 0.0035â µm. Simulations and experiments show that the proposed method can adaptively provide accurate envelope information after half-width reduction under the condition that only the approximate central wave-number a priori knowledge is used. Simultaneously, the proposed method is shown to be robust and effective.