Beating vibration

Error analysis and correction of a photoelastic method based on a pixelated polarization camera

We present a novel phase-based filtering algorithm designed to retrieve the Degree of Linear Polarization (DoLP) and Angle of Linear Polarization (AoLP) by leveraging the intrinsic properties of a pixelated polarization camera. Unlike conventional intensity-based filters, our approach utilizes complex phase values to estimate polarization parameters, offering a flexible and computationally efficient alternative. Each point is treated as an independent measurement, dependent solely on the kernel size, which enables the potential for real-time processing. Experimental and simulation evaluations under Gaussian noise conditions validate the robustness of our approach, demonstrating a high degree of consistency with standard methods. The ANOVA analysis results reflect this consistency across datasets, as indicated by the sum of squares (SS), mean squares (MS), and F-statistic values. This reinforces the reliability of the proposed algorithm and highlights its practical applicability in noise-affected environments. Our findings suggest that the proposed method provides a stable and adaptable solution for polarization parameter extraction, making it well-suited for applications in fields such as biomedical imaging, remote sensing, and industrial inspection, where real-time performance and noise resilience are critical.

Ellipsometric Surface Plasmon Resonance (SPR) sensors are known for their relatively simple optical configuration compared to interferometric and optical heterodyne phase interrogation techniques. However, most of the previously explored ellipsometric SPR sensors based on intensity measurements are limited by their real-time applications because phase or polarization shifts are conducted serially. Here we present an ellipsometric SPR sensor based on a Kretschmann-Raether (KR) diverging beam configuration and a pixelated microgrid polarization camera. The proposed methodology has the advantage of real-time and higher precision sensing applications. The short-term stability of the measurement using the ellipsometric parameters tanψ and cos(Δ) is found to be superior over direct SPR or intensity measurements, particularly with fluctuating sources such as laser diodes. Refractive index and dynamic change measurements in real-time are presented together with Bovine Serum Albumin (BSA)-anti-BSA antibody binding to demonstrate the potential of the developed sensor for biological sensing applications with a resolution of sub-nM and down to pM with additional optimization. The analysis shows that this approach may provide the ultimate detection limit for SPR sensors.

We report variable shear interferometers employing liquid-crystal-based geometric-phase (GP) gratings. Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting capabilities in x- and y- direction and two axial shifts of the gratings to adjust the shear amount in x- and y- direction, i.e., these systems need control of four axes mechanically. Here we show that the GP gratings combined with a pixelated polarization camera give instantaneous-phase shifting so that no mechanical movement is necessary to obtain phase shifts. Furthermore, we show that a single fixed shear with a rotational shear axis provides a more robust selection of shears while requiring the control of only one mechanical axis. We verify this statement using spatial domain and frequency domain criteria. We further show that the resolution of the reconstructed wavefield depends not only on the numerical aperture of the imaging system, the pixel size of the detector, or the spatial coherence of the source but also on the ability to determine the shear amount accurately. To improve this, we report a methodology to accurately detect the shear amounts using the second derivative of the autocorrelation function of the measured holograms, which further relaxes the requirements on mechanical stability.

Phase analysis by differential interference contrast microscope using pixelated polarization camera

像素刻划偏振相机的高精度像素级偏振非均匀性矫正

This work presents a dynamic electronic speckle pattern interferometry (ESPI) system with out-of-plane sensitivity based on a pixelated polarization camera. The approach employs polarization-encoded phase-shifting interferometry, enabling the simultaneous acquisition of multiple phase-shifted speckle interferograms and allowing the temporal tracking of deformation fields induced by mechanical loading. From the four polarization-resolved interference patterns, the phase is retrieved using a Fourier-based phase demodulation approach, from which the out-of-plane displacement field is reconstructed. Experimental results obtained on galvanized steel plates, including samples with and without structural defects such as cracks, demonstrate the capability of the method to resolve spatial variations in dynamic deformation, which were introduced by a piezoelectric actuator to assess the temporal stability and repeatability of the proposed system. These results indicate that the proposed approach is suitable for non-destructive evaluation and dynamic deformation monitoring of metallic components under mechanical stress.

Inner surface micro-scale topography is a concerned aspect in precise pipe-type workpiece manufacturing. To realize nondestructive measurement of pipe-type workpieces, in this paper a compact side-viewing interference microscope (CSIM) is proposed and a prototype is developed. Based on the Michelson-type configuration, a special interference objective is designed, in which the object plane is placed at the side of the objective to realize side viewing. To avoid mechanical scanning and reduce the measuring head size, a polarization interferometric method is employed by using a pixelated polarization camera to achieve phase shifting. The response of four polarization channels is calibrated with a simple spatial carrier method, and the surface reconstruction error is reduced by half with least-squares fittings compensation. Experiments verify that the CSIM achieves high axial resolution and roughness measurement accuracy up to the sub-nanometer level. Two pipe-type workpieces made of different materials, of which the minimum diameter is 42 mm, are successfully measured with the developed CSIM.

In this investigation, we propose a simple and effective lateral shearing interferometer based on a polarization grating. In the lateral shearing device, an incident beam is split into two beams by a polarization grating, and the returning beams can be laterally shifted after reflecting off a flat mirror and passing through the polarization grating again. These two beams are not only laterally shifted, but also their polarization states are orthogonal to each other as circular polarizations. With a single image obtained by a pixelated polarization CMOS camera, the proposed LSI can obtain the phase map corresponding to the x-sheared interferogram, and the other phase map can be calculated from another single image obtained by 90° rotation of the shearing device. Then, the original wavefront corresponding to the surface figure of the specimen can be reconstructed by wavefront reconstruction algorithms. In the experiments, various wavefronts generated by concave mirrors and a deformable mirror were measured and compared with those of a commercial Shack-Hartmann sensor.