Polarization Distribution Research Articles

Compact detector for vector vortex beams by polarization holography

Vector vortex beams (VVBs) have garnered significant attention for their potential to revolutionize applications such as high-resolution imaging and quantum communication. The development of an easy-to-use and effective method for representing the spatially inhomogeneous polarization distribution of VVBs is imperative. In this paper, we propose what we believe to be a novel compact detector for quickly and accurately measuring the polarization distribution of arbitrary VVBs by means of polarization holography. When a VVB illuminates the detector, multiple diffracting beams appear simultaneously that can be used to get the VVB’s polarization distribution. Incidentally, it can also measure the state of polarization of a scalar beam, which can be considered a special case of spatially inhomogeneous polarization. Experimental results confirm the detector's measurement accuracy, positioning it as a promising tool for advanced optical applications.

Operation of Photoeelectron Spectrometers for Non-Invasive Photon Diagnostics at the European X-Ray Free Electron Laser

Angle-resolved photoelectron spectrometers with microchannel plate detectors and fast digitizer electronics are versatile and powerful devices for providing non-invasive single-shot photon diagnostics at a MHz repetition rate X-ray free-electron lasers. In this contribution, we demonstrate and characterize the performance of our two operational photoelectron spectrometers for the application of hard X-rays and soft X-rays as well as new automation tools and online data analysis that enable continuous support for machine operators and instrument scientists. Customized software has been developed for the real-time monitoring of photon beam polarization and spectral distribution both in single-color and two-color operation. Hard X-ray operation imposes specific design challenges due to poor photoionization cross-sections and very high photoelectron velocities. Furthermore, recent advancements in machine learning enable resolution enhancement by training the photoelectron spectrometer together with an invasive high-resolution spectrometer, which generates a response function model.

An Optimized Public Opinion Communication System in Social Media Networks Based on K-means Cluster analysis

This study proposes a public opinion monitoring model that combines the K-means clustering algorithm with Particle Swarm Optimization (PSO) to enhance the accuracy and effectiveness of public opinion monitoring on social media. The model’s performance across various dissemination indicators is studied in detail. Through experiments conducted on social media datasets, the study comprehensively evaluates the model from four dimensions: dissemination speed, scope, depth, and sentiment dissemination effectiveness. The experimental results indicate that the proposed optimization model excels in multiple areas, particularly in dissemination depth and sentiment dissemination effectiveness. Specifically, in the three dimensions of dissemination speed, the proposed model achieves scores of 4.3, 4.2, and 4.4 in initial dissemination speed, decay speed, and peak dissemination speed, respectively. In the dimensions of user coverage, geographic coverage, and platform coverage under dissemination scope, the model scores 4.4, 4.5, and 4.3, demonstrating a broad dissemination capability. Additionally, in the dimensions of hierarchical dissemination depth and key node influence within dissemination depth, the model scores 4.3 and 4.5, indicating excellent performance in multi-level dissemination and key node activation. In sentiment dissemination effectiveness, the model receives scores of 4.4, 4.5, and 4.4 in emotional tendency change, polarity distribution, and diffusion intensity, showcasing its advantages in sentiment classification and dissemination. Sensitivity analysis further validates the model’s sensitivity to parameter settings, with experiments showing that reasonable adjustments to parameters such as the K value, PSO inertia weight, and learning factors can reduce the Sum of Squared Errors to 3209.72. Meanwhile, it can improve clustering purity to 0.822 and raise the Rand index to 0.623. Therefore, this study offers an efficient and reliable solution for public opinion monitoring on social media, providing valuable reference significance.

PixPol: An In-Water Multispectral Polarized Upwelling Radiance Distribution Camera System

Abstract PixPol is an in-water multispectral polarized upwelling radiance distribution fisheye camera system. Its imaging sensors utilize a pixel-level polarizer structure allowing for polarimetric retrieval from one image capture, offering an advantage compared to other in-water polarimetric fisheye camera systems that require information from multiple images. When submerged, PixPol images a scene from which the first three Stokes parameters are derived at an angular resolution of 1° within a field of view that encompasses all azimuthal angles up to an elevation of 43° from nadir. For all viewing angles, Stokes parameter I and the linear polarization parameters, Q/I and U/I, are retrieved with an interpixel uncertainty of ±5%, ±0.02%, and ±0.02%, respectively. From these parameters, an uncertainty of ±0.01 is attained for the degree of linear polarization and ±0.9° for the angle of linear polarization. A description of the camera system, its radiometric and polarization calibration, and the associated uncertainties are described. Example images of the distribution of downwelling polarized light in the sky just above the ocean’s surface and upwelling polarized light just below the surface are provided.

Spin angular momentum and optical chirality of Poincaré vector vortex beams

Abstract The optical chirality and spin angular momentum of structured scalar vortex beams has been intensively studied in recent years. The pseudoscalar topological charge $\ell$ of these beams is responsible for their unique properties. Constructed from a superposition of scalar vortex beams with topological charges $\ell_\text{A}$ and $\ell_\text{B}$, cylindrical vector vortex beams are higher-order Poincar'e modes which possess a spatially inhomogeneous polarization distribution. Here we highlight the highly tailorable and exotic spatial distributions of the optical spin and chirality densities of these higher-order structured beams under both paraxial (weak focusing) and non-paraxial (tight focusing) conditions. Our analytical theory can yield the spin angular momentum and optical chirality of each point on any higher-order or hybrid-order Poincar'e sphere. It is shown that the tunable Pancharatnam topological charge $\ell_{\text{P}} = (\ell_\text{A} + \ell_\text{B})/2$ and polarization index $m = (\ell_\text{B} -\ell_\text{A})/2$ of the vector vortex beam plays a decisive role in customizing their spin and chirality spatial distributions. We also provide the correct analytical equations to describe a focused, non-paraxial scalar Bessel beam.

Fractional-order hybridly polarized vector beams: generation, focusing, propagation, and spatial self-phase modulation

As a class of integer-order vector beams, hybridly polarized vector beams (HPVBs) are widely used in focus shaping, femtosecond laser filamentation, linear and nonlinear polarization evolution, etc. Recently, fractional-order vector beams have gained widespread interest due to their more control parameters, rich photophysical properties, and novel nonlinear optical phenomena. In this work, we report the experimental generation, focusing and propagation characteristics, and spatial self-phase modulation (SSPM) phenomenon of fractional-order HPVBs. It is shown that during the focusing and propagation processes, the intensity pattern of fractional-order HPVBs develops from a near-Gaussian structure in the incident plane to an asymmetric structure in both the focal field and the far field. Meanwhile, their distributions of state of polarization (SoP) also evolve, although it remains a hybrid polarization distribution overall. When the focused fractional-order HPVBs pass through the nonlinear optical sample, the far-field self-diffraction intensity pattern displays an irregular concentric multi-ring structure with a hybrid polarization distribution. It is found that the nonlinear medium not only modulates the far-field intensity pattern of fractional-order HPVBs but also controls their SoP distribution. This symmetric breaking HPVB has potential application prospects in optical micro-manipulation, light-matter interaction, optical spin-orbit conversion, etc.

Generation of scalar and vector beams with longitudinally varying polarization based on all-silicon metasurfaces

Beams with longitudinally continuously varying polarization provide a new application dimension in fields such as optical communication and optical manipulation. The small-sized and multifunctional metasurfaces have been used to generate scalar or vector beams whose polarizations vary along the propagation direction within a single polarization mode. However, dual-mode beams with longitudinally varying polarization can further increase the dimension of manipulation, but they have been rarely explored. Here, we propose a scheme based on the spatial partitioning method for designing dual-mode beams with longitudinally evolving polarization. To validate the proposed scheme, we demonstrate three dual-mode beams generated by all-silicon metasurfaces which have evolving polarization from scalar to vector, scalar vortex to vector vortex, and first-order to second-order cylindrical vector, respectively. The transverse polarization distributions of these beams depend on their longitudinal position. The different focal lengths of the orthogonal circularly polarized components and the design of long focal depth make it possible to change the polarization distribution longitudinally. The optical fields generated based on the proposed scheme are expected to be applied in depth detection and optical manipulation.

A novel animal model of spontaneous epilepsy: Cdk5 knockout in pericyte-specific mice.

Changes in neurovascular unit components and their interactions play a crucial role in epileptogenesis and the pathological process of epilepsy. Currently, there is a lack of animal models that can accurately reflect the etiological impact of cerebrovascular lesions on epilepsy. In this study, we constructed cyclin-dependent kinase 5 conditional knockout mice in Cspg4 (pericyte marker)-positive cells using the Cre-LoxP system. The results revealed that this strain of mice exhibited significant seizure behaviors and epileptiform brain waves, loss of hippocampal and amygdala neurons, astrogliosis, decreased pericyte coverage, and reduced AQP4 polar distribution. Herein, we have developed a novel mouse model of spontaneous epilepsy, providing a critical animal model for studying the involvement of neurovascular unit factors in the development and progression of epilepsy.

On the Shift of the Maximum of the Polar Angular Distribution of Sputtered Atoms in the MD Model of the (001) Ni Face Sputtering

Using an up-to-date full molecular dynamics model of sputtering of single crystals, taking into account the incidence of ions on the surface, the peculiarities and mechanisms of atom sputtering during bombardment of the (001) Ni face with 200 eV Ar ions are studied for two target temperatures. It is shown for the first time that with an increase in the energy of sputtered atoms, not only the maximum of their polar angular distribution in the azimuthal direction toward the Wehner spots, but also the maximum of the polar angular distribution integrated over the azimuthal angles shifts first toward the normal to the surface, and then in the opposite direction. The polar distribution integrated over the azimuthal angle is formed by atoms ejecting from the surface at much larger polar angles than in the final (observed) distribution. Both effects are explained in terms of the surface mechanism of single crystal sputtering.

Generating sub-diffraction microwave needle beam for nondestructive testing by multifunctional transmissive metasurfaces

Sub-diffraction needle beams with high intensity, sub-diffraction focal size, and long depth of focus (DOF) have attracted many researchers’ attention. However, the traditional methods for needle beam generation typically require many devices, such as phase elements, amplitude filters, and lens, which leads to a complex and bulky system and unfavorable for their integration. To address these challenges, we use a single multifunctional transmissive metasurface to convert a linearly polarized plane wave into a needle beam in the microwave range. The guided wave inspired unit cells of the proposed metasurface is designed to simultaneously and independently modulate the polarization and phase of transmitted waves. By imposing the desired polarization and phase distributions on the metasurface, the proposed multifunctional transmissive metasurface can efficiently generate a needle beam with subdiffraction size and extended DOF at 10 GHz when it is illuminated by an x-polarized wave. The proposed metasurface is fabricated, and a sub-diffraction needle beam with good performance is obtained in our measurements. In addition, a proof-of-concept of a high-resolution nondestructive testing experiment based on our designed metasurface is accomplished. Our work is expected to have potential applications in nondestructive testing of materials and structures.

Continuous theta burst stimulation ameliorates cognitive deficits in microinfarcts mice via inhibiting glial activation and promoting paravascular CSF-ISF exchange

Microinfarcts are widespread in the elderly, accompanied by varying degrees of cognitive decline. Continuous theta burst stimulation (cTBS) has been demonstrated to be neuroprotective on cognitive dysfunction, but the underlying cellular mechanism has been still not clear. In the present study, we evaluated the effects of cTBS on cognitive function and brain pathological changes in mice model of microinfarcts. The spatial learning and memory was assessed by Morris water maze (MWM), Glymphatic clearance efficiency was evaluated using in vivo two-photon imaging. The loss of neurons, activation of astrocytes and microglia, the expression and polarity distribution of the astrocytic aquaporin-4 (AQP4) were assessed by immunofluorescence staining. Our results showed that cTBS treatment significantly improved the spatial learning and memory, accelerated the efficiency of glymphatic clearance, up-regulated the AQP4 expression and improved the polarity distribution of AQP4 in microinfarcts mice. Besides, cTBS treatment increased the number of surviving neurons, whereas decreased the activated astrocytes and microglia. Our study suggested that cTBS accelerated glymphatic clearance and inhibited the excessive gliogenesis, which ultimately exerted neuroprotective effects on microinfarcts mice.

Flexible focal array engineering with a binary array vector optical field

In recent years, the vector optical field (VOF) with space-variant polarization distribution has attracted great attention due to its unexpected effects and applications in a wide range of areas. The focal engineering plays the most important role, as the focused VOF provides various interesting properties. Here, we propose a kind of binary array VOF (BA-VOF), which can be applied in focal array engineering. The BA-VOF comprises an array of the first base field of radially polarized VOF and an array of the second base field of superposed subfields with phase modulations. We theoretically design and experimentally generate the BA-VOF. Based on the BA-VOF, we present a flexible method to manipulate the amount of the focal spots in the focal array. Moreover, the polarization state and spin angular momentum of each focal spot in the focal spot array can also be flexibly manipulated. The BA-VOF and the flexibly manipulated focal array are inspirable in the area of structured light, which can be applied in regions needing focal engineering, such as optical tweezers, optical fabrication, optical imaging, and so on.

Experimental generation of scalar and vector vortex Pearcey-Gauss Beams

Abstract In this manuscript, we put forward two new types of structured light beams, the vortex Pearcey-Gauss (VPeG) beam, with a homogeneous polarisation distribution, and the vector vortex Pearcey-Gauss (VVPeG) beam, with a non-homogeneous polarisation distribution. The latter is generated as a non-separable superposition of the spatial and polarisation degrees of freedom of light. We achieve their experimental realization through the combination of a spatial light modulator, which creates a scalar Pearcey-Gauss beam, and a q-plate which transforms it into a vortex or a vortex vector beam, depending on its input polarisation state. Their intensity and polarisation distributions along the propagation direction were determined through Stokes polarimetry, which was compared with numerical simulations. As demonstrated, the VVPeG beam evolves from an all-linear polarisation distribution to an approximately full Poincar'e beam. The proposed vector beams add to the extensive family of non-separable states of light. We anticipate that both types of beams will find applications in fields as diverse as optical metrology and tweezers, amongst others.

Multiple Multicolored 3D Polarization Knots Arranged along Light Propagation.

Polarization and color play essential roles in understanding optical phenomena and practical applications. Customized three-dimensional (3D) light fields, characterized by specific polarization and color distributions, have garnered growing interest owing to their unique optical attributes and expanded capacity for information encoding. To align with the ongoing trend of compactness and integration, it is desirable to develop lightweight optical elements that can simultaneously control polarization and color in 3D space. Although engineering longitudinally variable 3D optical structures with predesigned color and polarization information can add more degrees of freedom and additional capacity for information encoding, it has not been reported. We propose a metasurface approach to generating multiple 3D polarization knots along the light propagation direction. Each knot features two colors and an engineered 3D polarization profile. Different multicolored 3D polarization knots are obtained by controlling the observation region along the light propagation. Our approach simultaneously combines polarization, color, and longitudinal control in 3D environment, offering extra degrees of freedom for engineering complex vector beams. The unique properties of the developed metadevices, together with the design flexibility and compactness of metasurface, pave the way for polarization systems with small volumes applicable to some areas such as complex structured beams and encryption.

Optical phase image encryption using stokes parameters and singular value decomposition

Abstract In this paper, we propose an optical asymmetric phase image encryption method in which the vectorial light field is used to encode the data. In transverse plane, the vectorial light field has spatially varying polarization distributions where we are allowed to have a greater number of degrees of freedom. In this scheme, the input image is first phase encoded and then modulated by a phase encrypting key, synthesized from the speckles obtained by the scattering of Hermite–Gaussian beams. The modulated image is further processed using fractional Fourier transform with a specific order (α). A pixel scrambling operator is utilized to increase the randomness to further enhance the security and singular value decomposition approach is employed to add the nonlinearity in the encryption process. Now, the stokes parameters, i.e. S 1 and S 2 are calculated using the light intensities correspond to different polarizations. S 1 is used as the encrypted image for transmission and S 2 is reserved as one of the private decryption keys. The robustness of the proposed technique is tested against various existing attacks, such as known plaintext attack, chosen plaintext attack, and contamination attacks. Numerically simulated results validate the effectiveness and efficiency of the proposed method.

Micro‐Mechanical Analysis for Residual Stresses and Shakedown of Cohesionless‐Frictional Particulate Materials Under Moving Surface Loads

AbstractResidual stresses and shakedown have been successfully presented by two‐dimensional numerical experiments based on the discrete element method (DEM), wherein a cohesionless‐frictional material under moving surface loads was replicated through irregular‐shaped particles. With surface loads below the shakedown limit, both permanent deformations and residual stresses cease to accumulate and the numerical structure shakes down after a number of load passes. Corresponding micro‐mechanical analyses indicate that strong forces and normal forces make a dominant contribution to residual stresses. Besides, averaged magnitudes of interparticle forces and corresponding total contact numbers initially change with load passes, and their final variation trends will differ as the structure shakes down or not. Furthermore, polar distributions of interparticle forces and contacts have been presented, and variations of their preferential orientations were emphasised. Lastly, the fabric tensor and anisotropy of resultant forces were studied, presenting the anisotropy weakening of macro‐stress fields, induced by developments of residual stresses.

Second-harmonic radiation by on-chip integrable mirror-symmetric nanodimers with sub-nanometric plasmonic gap

Abstract Second-harmonic generation (SHG) facilitated by plasmonic nanostructures has drawn considerable attention, owing to its efficient frequency up-conversion at the nanoscale and potential applications in on-chip integration and nanophotonic devices. Herein, we present a nanodimer array fabricated by nanoimprinting, composed of nanofinger-pair symmetrically leaning at an off-angle with a well-defined sub-nanometric gap. Commonly, geometric symmetry would suppress the far-field SHG due to the near-field cancelling of symmetric surface SH polarization. However, we find that the light-induced surface SH polarization distribution along the wave-vector of incidence could be influenced by the off-angle, which is consistent to the requirement of SH polarization symmetry-breaking in symmetric metallic nanocavity. A dramatic enhancement of far-field SHG is achieved by tuning the off-angle of nanofinger-pair, even approaching up to over 4 orders of magnitude for an optimal value. The demonstration of SHG enhancement on our well-defined plasmonic nanodimer provides a new way of on-chip integration to activate high-efficient SH radiation, which might be potential for applications in novel nonlinear optical nanodevices with remarkable efficiency and sensitivity.

Synergistically flexible-robust effects mediate the dynamic reconfiguration of perylene diimide polymer to enhance piezo-photocatalytic nitrate reduction

Identifying the spatial dynamic reconstruction of π-conjugated polymers for efficient carrier transport and controlling the intermediate process of the reaction are urgent and formidable challenges. In this study, a fresh perspective has emerged proposing to synergistically enhance the adaptability and resilience of dynamic torsion patterns in π-conjugated polymers to mediate charge separation and molecular activation. Excitingly, the highest flexible-robust structure and polarity of naphthalene-linked perylene diimide polymer (N-PDA) demonstrates a highest nitrate reduction rate of 5.36 mmol g−1 h−1 under light irradiation and ultrasonic condition, which is 7.5 times that of H-PDA. Theoretical calculations and experimental observations indicate that the strongest flexible-robust structure of N-PDA enhances the inclination of the rigid plane and atomic bond length, resulting in an accelerated uneven distribution of charges, molecular polarity, and electronic coupling to facilitate charge separation dynamics. Moreover, it exposes active sites that promote the adsorption and activation of NO3- ions while simultaneously regulating intermediate hydrogenation processes. Our study offers innovative prospects for enhancing catalytic efficiency through the implementation of spatial steric configuration of π-conjugated polymers.

Enhancing the sensitivity of spin-exchange relaxation-free magnetometers using phase-modulated pump light with external Gaussian noise

An optical pumping scheme is proposed for reducing the gradient of electron spin polarization and suppressing light source noise in a spin-exchange relaxation-free magnetometer. This is achieved by modulating only the phase of a narrow-linewidth pump light field with external Gaussian noise. Compared to the absence of phase modulation, the uniformity of electron spin polarization was improved by over 40%, and the light-frequency noise suppression ratio of the magnetometer was enhanced by 4.3 times. Additionally, the response of the magnetometer was increased by 54%, resulting in a sensitivity of 0.34 fT/Hz1/2 at 30 Hz. The applicability of this scheme can extend to other optical pumping experiments involving large atom ensembles requiring uniform electron spin polarization distribution, which is beneficial for developing ultra-high sensitivity and high stability magnetometers essential for magneto-cardiography and magneto-encephalography research applications.

Intestinal vascular diseases misdiagnosed as Crohn ​disease: analysis of 13 cases

Behçet ​disease (BD), enterocolic lymphocytic phlebitis (ELP), idiopathic myointimal hyperplasia of mesenteric veins (IMHMV), and mesenteric arteriovenous dysplasia/vasculopathy (MAVD/V) are rare vascular diseases (VDs) that cause bowel ischaemia, often presenting with a histological pattern resembling chronic enteritis, leading to diagnostic confusion with Crohn ​disease (CD). In this retrospective study, we compared the clinical and pathological characteristics of these VDs with those of CD. The study cohort comprised 13 patients misdiagnosed with CD but later identified as having VDs, including five, three, two, and three patients with BD, ELP, IMHMV, and MAVD/V, respectively. Moreover, 15 patients diagnosed with CD served as the control group. Data on disease history, patient demographics, symptoms and signs, endoscopic findings, clinical diagnosis, and follow-up status were collected, and the histological features of VDs were compared with those of CD. Despite substantial overlap in clinical and pathological characteristics between VDs and CD, several histological features were helpful in differentiating the two conditions. Intestinal stenosis, multisegmental disease, transmural inflammation, inflammatory polyps, submucosal lymphangiectasia, intramural abscesses, and epithelioid granulomas were significantly more frequent in patients with CD (p<0.001). In contrast, toxic ischaemic changes and vascular lesions were significantly more frequent in patients with VDs (p<0.001). The location of diseased vessels varied widely in patients with VDs, whereas vascular changes were limited to areas with more severe inflammation in those with CD. Furthermore, inflammatory cells within diseased vessels exhibited a polarised distribution in cases of CD, manifesting in two distinct patterns: pattern 1, where the inflammatory cells are densely populated in the outer layer of the vessel wall and sparsely populated in the inner layer; pattern 2, where the inflammatory cells are densely populated on the side with the ulcer and sparsely populated on the opposite side. Vascular occlusion, which was observed in all patients with VDs, was rare in those with CD. In summary, VDs and CD can be distinguished through careful histological analysis, particularly focusing on characteristics of vascular changes, in combination with medical history.