Polarimetric Detection Research Articles

Multiwavelength Optical Rotation Detection: An Effective Approach for the Recognition of Analytical and Semi‐Preparative HPLC Enantioseparation of the Chiral Pheromone Olean and Its Stereochemical Characterization

ABSTRACTOlean is the chiral spiroacetal sex pheromone of the female olive fruit fly Bactrocera oleae. Laboratory tests have demonstrated that the (R)‐(−)‐olean enantiomer is active on males, whereas females respond to (S)‐(+)‐olean. Here we present the first HPLC enantioseparation of olean using polysaccharide derivatives as chiral stationary phases and a polarimetric detector equipped with a micro‐flow cell capable of detecting optical rotation at six different wavelengths. Unlike blind UV detection, the polarimetric detector allows the chiral spiroacetal, which lacks a chromophore, to be detected as bisegnate peaks, indicating the opposite sign of the optical rotation. The HPLC enantioseparation was optimized on the coated type amylose‐based Chiralpak AS‐H CSP using a mobile phase consisting of n‐hexane‐2‐propanol 99.99:0.01 (v/v). These conditions were scaled up to a semi‐preparative level and allowed resolution of 2.5 mg of racemic sample in 5 min. Multiwavelength optical rotation detection during HPLC enantioseparation of racemic samples provides a direct readout of the stereochemistry of olean and allows tracking of virtual optical rotation dispersion curves without the need for preliminary collection of enantiomeric samples by semi‐preparative HPLC.

Twisted hyperbolic van der Waals crystals for chip-scale full Stokes mid-infrared polarization detection

Abstract Investigating the polarization properties of light in the mid-infrared (mid-IR) spectrum is crucial for molecular sensing, biomedical diagnostics, and IR imaging system technologies. Traditional methods, limited by bulky size and complicated fabrication process, utilize large rotating optics for full Stokes polarization detection, impeding miniaturization and accuracy. Naturally occurring hyperbolic van der Waals (vdW) material based devices can address these challenges due to their lithography-free fabrication, ease of integration with chip-scale platforms and room-temperature operation. This study designs a chip-integrated polarimeter by performing multi-objective optimization for efficient exploration of the design parameter space. The spatial division measurement scheme used incorporates six precisely designed linear and circular polarization filters, achieving high extinction ratios exceeding 30 dB and transmittance surpassing 50%, with fabrication tolerance of film thickness up to 100 nm. The proposed device represents a significant advancement in polarimetric detection, providing a compact, cost-effective solution and opens new avenues for on-chip mid-IR polarimetric detection in next-generation ultra-compact optical systems.

Infrared Optical Anisotropy in Quasi‐1D Hexagonal Chalcogenide BaTiSe3

AbstractPolarimetric infrared (IR) detection bolsters IR thermography by leveraging the polarization of light. Optical anisotropy, i.e., birefringence and dichroism, can be leveraged to achieve polarimetric detection. Recently, giant optical anisotropy is discovered in quasi‐1D narrow‐bandgap hexagonal perovskite sulfides, A1+xTiS3, specifically BaTiS3 and Sr9/8TiS3. In these materials, the critical role of atomic‐scale structure modulations in the unconventional electrical, optical, and thermal properties raises the broader question of the nature of other materials that belong to this family. To address this issue, for the first time, high‐quality single crystals of a largely unexplored member of the A1+xTiX3 (X = S, Se) family, BaTiSe3 are synthesized. Single‐crystal X‐ray diffraction determined the room‐temperature structure with the P31c space group, which is a superstructure of the earlier reported P63/mmc structure. The crystal structure of BaTiSe3 features antiparallel c‐axis displacements similar to but of lower symmetry than BaTiS3, verified by the polarization dependent Raman spectroscopy. Fourier transform infrared (FTIR) spectroscopy is used to characterize the optical anisotropy of BaTiSe3, whose refractive index along the ordinary (E ⊥ c) and extraordinary (E ‖ c) optical axes is quantitatively determined by combining ellipsometry studies with FTIR. With a giant birefringence Δn ∼ 0.9, BaTiSe3 emerges as a new candidate for miniaturized birefringent optics for mid‐wave infrared to long‐wave infrared imaging.

Prospects for the Detection of the Sgr A* Photon Ring with Next-generation Event Horizon Telescope Polarimetry

The Event Horizon Telescope (EHT) has imaged two supermassive black holes, Messier 87* (M87*) and Sagittarius A* (Sgr A*), using very-long-baseline interferometry (VLBI). The theoretical analyses of each source suggest magnetically arrested disk (MAD) accretion viewed at modest inclination. These MADs exhibit rotationally symmetric polarization of synchrotron emission caused by symmetries of their ordered magnetic fields. We leverage these symmetries to study the detectability of the black hole photon ring, which imposes known antisymmetries in polarization. In this Letter, we propose a novel observational strategy based on coherent baseline averaging of polarization ratios On a rotating basis to detect the photon ring with 345 GHz VLBI from the Earth’s surface. Using synthetic observations from a likely future EHT, we find a reversal in polarimetric phases on long baselines that reveals the presence of the Sgr A* photon ring in a MAD system at 345 GHz, a critical frequency for lengthening baselines and overcoming interstellar scattering. We use our synthetic data and analysis pipeline to estimate requirements for the EHT using a new metric: SNRPR, the signal-to-noise ratio of this polarimetric reversal signal. We identify long, coherent integrations using frequency phase transfer as a critical enabling technique for the detection of the photon ring and predict a SNRPR ∼ 2−3 detection using proposed next-generation Event Horizon Telescope parameters and currently favored models for the Sgr A* accretion flow. We find that higher sensitivity, rather than denser Fourier sampling, is the most critical requirement for polarimetric detection of the photon ring.

Magnetic sensitivity enhancement via polarimetric excitation and detection of an ensemble of NV centers

The negatively charged nitrogen-vacancy center (NV) presents remarkable spin-dependent optical properties that make it an interesting tool for magnetic field sensing. In this paper we exploit the polarization properties of the NV center absorption and emission processes to improve the magnetic sensitivity of an ensemble of NV centers. By simply equipping the experimental set-up of a half-wave plate in the excitation path and a polarizer in the detection path we demonstrate an improvement larger than a factor of two on the NV center magnetic sensitivity.

Analytical Coherent Detection in High-Resolution Dual-Polarimetric Sea Clutter with Independent Inverse Gamma Textures

Polarization diversity has been widely used in maritime radars to improve target detection performance. Full utilization of the polarimetric characteristics of sea clutter is the key to designing effective polarimetric detectors. For high-resolution maritime radars, the HH-HV dual-polarization is an affordable and effective mode to monitor small targets, owing to the simple configuration of single-polarimetric transmit and dual-polarimetric reception and lower clutter powers at the HH and HV polarizations. Enlightened by the analytical coherent detector in compound-Gaussian clutter with inverse Gamma texture, this paper investigates dual-polarimetric coherent detection in dual-polarimetric compound-Gaussian clutter with independent inverse Gamma distributed textures. The analytical dual-polarimetric near-optimum coherent detector is derived, which is a fusion of the generalized likelihood ratio test linear threshold detectors (GLRT-LTDs) at the two polarizations. For short, it is referred to as the P-GLRT-LTD. It is proven that the P-GLRT-LTD is of constant false alarm rate with respect to the Doppler steering vector, scale parameters of textures, and speckle covariance matrices. Moreover, the thresholds of the P-GLRT-LTD are given analytically. Experiments using simulated sea clutter data with the estimated scale and shape parameters from the two measured intelligent pixel processing radar (IPIX) datasets and two measured IPIX datasets with test targets are made to compare P-GLRT-LTD with other existing dual-polarimetric coherent detectors. The results show that the P-GLRT-LTD attains the same detection performance as the existing best-performance detector. The P-GLRT-LTD has a lower computational cost than the existing best-performing one.

The position resolution of the Gas Microchannel plate Pixel Detector

The Gas Microchannel plate Pixel Detector (GMPD) is purposefully designed and manufactured for astrophysical X-ray polarization detection, slated for use in various space missions such as the Cosmic X-ray Polarization Detector (CXPD) CubeSat, Low Energy Polarimeter Detector (LPD/POLAR-2), and the Chasing All Transients Constellation Hunters (CATCH). Past research has explored the polarization and spectral performance of GMPD. This study, for the first time, experimentally investigates its imaging characteristics to validate its imaging capabilities. Utilizing a deconvolution method, we measured the position resolution of GMPD, revealing distinctions in the detector's imaging capabilities for X-rays of varying energies and in orthogonal directions. These research findings will provide targeted insights for optimizing the photoelectron track reconstruction algorithm and correcting systematic effects in polarization measurements for future applications of GMPD.

Enhancement of Small Ship Detection Using Polarimetric Combination from Sentinel−1 Imagery

Speckle noise and the spatial resolution of the Sentinel−1 Synthetic Aperture Radar (SAR) image can cause significant difficulties in the detection of small objects, such as small ships. Therefore, in this study, the Polarimetric Combination-based Ship Detection (PCSD) approach is proposed for enhancing small ship detection performance, which combines three different characteristics of polarization: newVH, enhanced VH, and enhanced VV. Employing the Radar Cross Section (RCS) value in three stages, the newVH was utilized to detect Automatic Identification System (AIS) -ships and small ships. In the first step, the adaptive threshold (AT) method was applied to newVH with a high RCS condition (>−10.36 (dB)) for detecting AIS-ships. Secondly, the first small ship target was detected with the maximum suppression of false alarms by using the AT with a middle RCS condition (>−16.98 (dB)). In the third step, a candidate group was identified by applying a condition to the RCS values (>−23.01 (dB)), where both small ships and speckle noise were present simultaneously. Subsequently, the enhanced VH and VV polarizations were employed, and an optimized threshold value was selected for each polarization to detect the second small ship while eliminating noise pixels. Finally, the results were evaluated using the AIS and small fishing vessel tracking system (V-Pass) based on the detected ship positions and ship lengths. The average matching results from 26 scenes in 2022 indicated a matching rate of over 86.67% for AIS-ships. Regarding small ships, the detection performance of PCSD was 42.27%, which was over twice as accurate as the previous Constant False Alarm Rate (CFAR) ship detection model. As a result, PCSD enhanced the detection rate of small ships while maintaining the capacity for detecting AIS-equipped ships.

PODB: A learning-based polarimetric object detection benchmark for road scenes in adverse weather conditions

Due to its insensitivity to light intensity and the capability to capture multidimensional information, polarimetric imaging technology has been proven to have advantages over traditional intensity-based imaging techniques for object detection tasks in adverse environmental conditions, particularly in road traffic scenarios. Recently, with the rapid development of artificial intelligence technology, deep learning (DL)-powered object detection techniques can further enhance recognition accuracy and algorithm robustness. This improvement is made possible by the ability of DL technology to leverage large datasets and extract deeper levels of target-specific features. However, constructing large-scale polarimetric datasets poses challenges as obtaining polarimetric information requires multiple captures of intensity images. In other words, the workload is several times higher compared to traditional imaging techniques. To address the current scarcity of polarimetric datasets and evaluate the practical performance of various algorithms on polarimetric datasets, this paper proposes a Polarimetric Object Detection Benchmark (PODB) dataset. The PODB provides an integrated quality evaluation framework for DL-based object detection algorithms in complex road scenes by incorporating polarimetric imaging. Besides, we conducted extensive object detection experiments using the PODB, which allowed for a comprehensive validation and performance evaluation of effective benchmark algorithms. Furthermore, a physics-based multi-scale image fusion cascaded object detection neural network model is proposed. By combining the multidimensional information provided by polarized images with an adaptive learning multi-decision object detection neural network model, the recognition accuracy of complex road scenes in adverse weather conditions has been improved by approximately 10%. Additionally, we anticipate that PODB will serve as an effective platform for evaluating and comparing the performance of object detection algorithms, as well as providing researchers with a baseline for future studies in developing new DL-based methods.

Realizing Minimally Perturbed, Nonlocal Chiral Metasurfaces for Direct Stokes Parameter Detection.

Recent development in nonlocal resonance based chiral metasurfaces draws great attention due to their abilities to strongly interact with circularly polarized light at a relatively narrow spectral bandwidth. However, there still remain challenges in realizing effective nonlocal chiral metasurfaces in optical frequency due to demanding fabrications such as 3D-multilayered or nanoscaled chiral geometry, which, in particular, limit their applications to polarimetric detection with high-Q spectra. Here, we study the underlying working principles and reveal the important role of the interaction between high-Q nonlocal resonance and low-Q localized Mie resonance in realizing effective nonlocal chiral metasurfaces. Based on the working principles, we demonstrate one of the simplest types of nonlocal chiral metasurfaces which directly detects a set of Stokes parameters without the numerical combination of transmitted values presented from typical Stokes metasurfaces. This is achieved by minimally altering the geometry and filling ratio of every constituent nanostructure in a unit cell, facilitating consistent-sized nanolithography for all samples experimentally at a targeted wavelength with relatively high-Q spectra. This work provides an alternative design rule to realizing effective polarimetric metasurfaces and the potential applications of nonlocal Stokes parameters detection.

Pre-Processing of Simulated Synthetic Aperture Radar Image Scenes Using Polarimetric Enhancement for Improved Ship Wake Detection

Ship wake detection using synthetic aperture radar (SAR) imagery provides a way to obtain small marine ship information, but it often becomes unavailable and unreliable during a high sea state. Polarimetric information provides a potential way to solve this problem, which can enhance the ship target as well as the ship wake features. However, three challenges still exist in ship wake detection in polarimetric SAR imagery: the unwanted influences of bright and singular points on ship wake detection, the lack of performance analysis of wake detection by new-type polarimetric enhancement methods, and the difficulty of using the assessment criteria for ship wake detection. In this paper, we try to solve the above problems. Firstly, fully polarized SAR imagery of both ship turbulent and Kelvin wake is simulated based on the two-scale composite model, and the Polarimetric Whitening Filter (PWF) and Polarimetric Detection Optimization Filter (PDOF) are applied to the simulated fully polarized SAR imagery to enhance the ship wake features. Secondly, since the bright and singular points resulting from the ship echoes and the polarimetric enhancement methods may lead to misdetections, a logarithm process and z-score normalization pre-processing has been applied to the images. Then, a new assessment criterion for wake detection performance has been formulated, and the probability of missing detections (PMDs) and the probability of false alarms (PFAs) have been defined for two different requirements. And a Radon transform-based ship wake detection method for both ship turbulence and Kelvin wake has been carried out in horizontal–horizontal (HH), vertical–vertical (VV), horizontal–vertical (HV), PWF and PDOF SAR imagery. Finally, an analysis of the wake detection performance has been carried out. The PWF and PDOF can improve the wake detection performance by an average of nearly 50 percent compared with the HH and VV.

Persymmetric Adaptive Polarimetric Detection of Subspace Range-Spread Targets in Compound Gaussian Sea Clutter

Persymmetric Adaptive Polarimetric Detection of Subspace Range-Spread Targets in Compound Gaussian Sea Clutter

Deep learning-driven underwater polarimetric target detection based on the dispersion of polarization characteristics

Underwater target detection especially in turbidity environments is a crucial and challenging area of study due to its extensive applications. In this work, we propose an underwater target detection method that combines the dispersion of polarization characteristics with a neural network framework. The polarization dispersion distribution features are effective at reducing the influence of the scattering effect of particulate matter in a turbidity environment, and highlighting the polarization state variations, especially in the edge contour features between the target and background. According to the physical detection model of dispersion of polarization characteristics, the neural network is constructed to extract dispersion values of the angle of polarization (AOP) and degree of linear polarization (DOLP) from the underwater polarization image datasets with different turbidity levels, which we then used to train the network to map physical characteristic parameters of the target for the detection. When compared to target detection methods based on light intensity images and polarization characteristic images (AOP and DOLP), the experimental results indicate that the proposed network model with polarization dispersion images has a significant improvement in locating and identifying targets of different materials, particularly in high turbidity underwater environments. These results provide deeper understanding of polarization polarimetric target detection, and further improve the functionality of a polarimetric target detection optical system.

Potential of a Multistate Quantum Model for Full Polarimetric SAR Change Detection

Potential of a Multistate Quantum Model for Full Polarimetric SAR Change Detection

Rao test of polarimetric detection for targets with energy spillover in non-Gaussian clutter

In this paper, we address the problem of polarimetric detection for targets with energy spillover in non-Gaussian clutter. The polarization diversity and spillover of target energy to consecutive range bins are jointly exploited to enhance the performance of target detection. Two adaptive detectors are designed according to the Rao test, as well as its two-step implementation, i.e., 2S-Rao test. It is shown that the 2S-Rao test detector coincides with the existing generalized likelihood ratio test (GLRT) detector, whereas the Rao test detector is new, and outperforms the existing detectors in probability of detection. Experiments based on both simulated and real data illustrate the superiority of the proposed detector.

Spectral and polarimetric characterization of the Gas Microchannel plate Pixel Detector

The Gas Microchannel plate Pixel Detector (GMPD) is used to measure X-ray polarization in astrophysical sources, and is the prototype of the Low Energy Polarimeter Detector (LPD) in the POLAR-2 project. The choice of the detector's gas mixture has a profound impact on its sensitivity to polarized X-rays. Here, we present the characteristics of the GMPD filled with a mixture of 40% He and 60%DME at 0.8 atm. Using Bragg diffraction, we generated nearly fully polarized and monochromatic X-rays at an angle of approximately 45°, and for the first time, we measured the modulation factor and spectral capability at energies of 2.98 keV, 4.51 keV, 6.40 keV, and 8.05 keV. The energy resolution measured is 18% at 6.40 keV, inversely proportional to the square root of the X-ray energy. The measured modulation factors were close to those obtained for the GPD developed by INFN-Pisa and INAF/IASF-Rome, reaching approximately 0.5 above 6 keV, allowing a comparison of the sensitivity of the GMPD and GPD.

Polarimetric imaging-based cancer bladder tissue's detection: A comparative study of bulk and formalin-fixed paraffin-embedded samples

The polarimetry imaging technique as a promising technique for pathological diagnosis provides a handy tool for identifying and discriminating cancerous tissues. In this paper, the optical polarization properties of bulk bladder tissues without any further processing and Formalin-Fixed Paraffin-Embedded (FFPE) blocks of bladder tissues have been measured. The images of the Muller matrix for both normal and cancerous samples have been obtained and for quantitative analysis and to provide a more precise comparison, two methods have been applied; the Mueller matrix polar decomposition (MMPD), and the Mueller matrix transformation (MMT). The results have shown that some of the extracted parameters from these methods can be used to identify the microstructural differentiations between normal and cancerous tissues. The results revealed a good accord between the obtained optical parameters for bulk and FFPE bladder tissues. By measuring the polarimetric properties of the tissue right after resection, and also in the early stages of pathology (FFPE tissues), this method can be applied in vivo to perform an optical biopsy; Furthermore, this method has the potential to significantly shortens the duration of pathological diagnosis. The approach seems remarkable, simple, precise, and economical compared to the existing techniques for the detection of cancerous samples.

Front-End Electronics of CXPD for Measuring Transient X-Ray Sources

The Low Energy Polarization Detector (LPD), a payload of the POLAR-2 mission, is a soft X-ray polarization detector with a wide field of view and a large array aimed at measuring X-ray transients. These transients exhibit rapid intensity changes of several orders of magnitude, making it crucial for polarization detectors to have front-end electronics with low dead time, fast readout capabilities, high time resolution, and good energy resolution. In this paper, we present the design of the front-end electronics, which consist of a rolling shutter CMOS pixel charge sensor - Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , and a gas microchannel plate (GMCP) bottom amplifier circuit. Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ’s rolling shutter readout provides fast scanning of large pixel arrays without dead time and acquires two-dimensional images of photoelectron tracks. Meanwhile, the GMCP’s bottom amplifier circuit measures the energy and time of the X-ray. The front-end electronics are employed by the CubeSat CXPD (Cosmic X-ray Polarimeter Detector), a proto-flight model of the LPD, achieving a timing resolution of 19 ns, and an energy resolution of 16.5% for linearly polarized X-rays at 8 keV.

Polarimetric Range Extended Target Detection via Adaptive Range Weighted Feature Extraction

In ground static target detection, polarimetric high-resolution radar can distinguish the target from the strong ground clutter by reducing the clutter power in the range cell and providing additional polarimetric features. Since the energy of a target is split over several range cells, the resulting detection problem is called polarimetric range extended target (RET) detection, where all target scattering centers should be considered. In this paper, we propose a novel polarimetric RET detection method via adaptive range weighted feature extraction. Specifically, polarimetric features of range cells are extracted, and a pretrained attention-mechanism-based module is used to adaptively calculate range cells weights, which are used to accumulate the range cells features as detection statistics. While calculating weights, both amplitude and polarimetric features are considered. This method can make the most of polarization information and improve the accumulation effect, thus increasing the discrimination between targets and clutter. The effectiveness of the proposed method is verified compared to both popular energy-domain detection methods and existing feature-domain detection methods, and the results show that our method exhibits superior detection performance. Moreover, we further analyze our method on different target models and different clutter distributions to prove that our method is suitable for different types of targets and clutter.

Structural design and optimization of subwavelength grating polarizers for short infrared-wavelengths

Subwavelength grating (SWG) is currently the major component being applied in polarimetric detections in infrared wavelengths, owing to its unique advantages in miniaturized dimensions, integrability with the exiting planar focal plane array of photoelectronic detectors, and compatibility with semiconductor technology. However, the obstacle hindering the applications of the SWGs polarizer is the limited polarization performance of both the transmittance and the extinction ratio, despite substantial efforts have been reported. It has been well understood that SWG with short pitch and high aspect ratio is the solution for achieving high performance, which is a daunting challenge to nanofabrication. To overcome the technical bottleneck for highly dense gratings with high aspect ratio, this work proposed a structure with the metallic grating parasitically grown on the sidewalls of replicated dielectric lines/spaces by electron beam lithography, followed by an angled evaporation process of metal. Numerical simulations by a finite-difference time-domain method were carried out to optimize the structural dimensions for achieving both high transmittances and extinction ratios. Electron beam lithography together with angled depositions of an aluminum (Al) film was applied to fabricate the proposed SWG polarizers with the aspect ratio as high as 13:1. Optical characterizations demonstrated enhanced polarization performances in short infrared wavelengths from 1050 up to 1600 nm. The developed SWG polarizer and the fabrication technique possess advantages in the simplified process, lift off free and wafer scale prospect.