Polarization Selection Research Articles

An ultra-thin tri-functional coding metasurface based on frequency and polarization selection

An ultra-thin tri-functional coding metasurface based on frequency and polarization selection

3D Directional Assembly of Liquid Crystal Molecules.

The precise construction of hierarchically long-range ordered structures using molecules as fundamental building blocks can fully harness their anisotropy and potential. However, the 3D, high-precision, and single-step directional assembly of molecules is a long-pending challenge. Here, a 3D directional molecular assembly strategy via femtosecond laser direct writing (FsLDW) is proposed and the feasibility of this approach using liquid crystal (LC) molecules as an illustrative example is demonstrated. The physical mechanism for femtosecond (fs) laser-induced assembly of LC molecules is investigated, and precise 3D arbitrary assembly of LC molecules is achieved by defining the discretized laser scanning pathway. Additionally, an LC-based Fresnel zone plate array with polarization selection and colorization imaging functions is fabricated to further illustrate the potential of this method. This study not only introduces a 3D high-resolution alignment method for LC-based functional devices but also establishes a universal protocol for the precise 3D directional assembly of anisotropic molecules.

Selection rules in the excitation of the divacancy and the nitrogen-vacancy pair in 4 H - and 6 H -SiC

In this study, we address selection rules with respect to the polarization of the optical excitation of two color centers in 4H−SiC and 6H−SiC with potential for applications in quantum technology, the divacancy and the nitrogen-vacancy pair. We show that the photoluminescence of the axial configurations of higher symmetry (C3v) than the basal ones (C1h) can be canceled using any excitation (resonant or nonresonant) with polarization parallel to the crystal axis (EL||c). The polarization selection rules are determined using group-theoretical analysis and simple physical arguments showing that phonon-assisted absorption with EL||c is prohibited despite being formally allowed by group theory. A comparison with the selection rules for the silicon vacancy, another defect with C3v symmetry, is also carried out. Using the selection rules, we demonstrate selective excitation of only one basal divacancy configuration in 4H−SiC, the PL3 line, and discuss the higher contrast and increased Debye-Waller factor in the selectively excited spectrum. Published by the American Physical Society 2024

We care: A User-Focused Sentiment Analysis Framework for Social Media Interactions

This paper addresses the sentiment analysis of WhatsApp chats, focusing on the challenges and opportunities presented by conversational data. The introduction outlines the prevalence of sentiment analysis in social media platforms and the significance of accurate sentiment categorization. The literature review highlights previous work in sentiment analysis, emphasizing methods for categorizing sentiment polarity and feature selection. The proposed system introduces a comprehensive approach to sentiment analysis tailored to WhatsApp chats, considering the unique characteristics of conversational data. Key features include user-centric inclusion, nuanced extraction of sentiment, context-aware analysis, and effective handling of conversational nuances. The method section details the proposed system's emphasis on real-time sentiment tracking, user-specific sentiment scores, and integration with WhatsApp's API for broader applications. The results section summarizes the positive outcomes of the proposed method, including user-centric inclusion, nuanced extraction, context-aware illustration, and effective content handling. The future scope section discusses potential enhancements such as real-time sentiment alerts, multilingual support, detailed sentiment analysis, improved user feedback systems, personalized sentiment metrics, and collaboration capabilities. The conclusion highlights the significance of the "WeCare" sentiment analysis project in improving our understanding of digital conversations, particularly within the context of WhatsApp chats. The project's commitment to user-centric design, adaptability, and ethical considerations positions it as a dynamic tool for enhancing digital interactions and well-being. Finally, acknowledgments recognize the contributions of the development team and academic mentor.

Hydrophobic hypercrosslinked polymers prepared by secondary pore-forming method as excellent toluene adsorbents

In this work, inspired by molecular imprinting technology, we developed a secondary pore-forming method to chemically etch three hypercrosslinked polymers which are constructed from three novel hexapolar monomers containing imine groups, resulting in three novel hydrophobic porous hyper-crosslinked polymers (HCPs) pGly-TPA, pP-TPA and pBP-TPA. The structures were determined by FT-IR and solid-state 13C NMR spectroscopic techniques. The specific surface areas of pGly-TPA, pP-TPA and pBP-TPA are 694.1, 197.9 and 497.7 m2/g, respectively. All three porous polymers exhibit high hydrophobic properties with wetting angles of much greater than 90°. The breakthrough adsorption experiments revealed that the three prepared polymers exhibited significant adsorption capacity for toluene (322.05 mg/g for pGly-TPA, 114.43 mg/g for pP-TPA and 279.14 mg/g for pBP-TPA), but showed almost no adsorption for ethyl acetate, cyclohexane, and n-hexane, exhibiting certain molecular size and polarity selectivity. The adsorption behaviors of toluene on pGly-TPA, pP-TPA and pBP-TPA can be fit by the Boltzmann model and the Yoon-Nelson model, suggesting that the fixed bed has low mass transfer resistance. The adsorption rate is controlled by both external diffusion and intraparticle diffusion, as shown by the intraparticle diffusion model analysis. In addition, the adsorption capacity of toluene on pGly-TPA is almost unchanged under high humidity (70 %) or five adsorption–desorption processes, which demonstrates exceptional water-resistance and stability. This work is a reference for preparing novel hydrophobic HCPs using the secondary pore-forming method for removing VOCs from humid air.

Investigation of the polarization difference of the EM wave of an airborne EW system in the mode of coherent interference

Problem statement. Coherent interference generated from two or more points makes it possible to change the amplitude-phase distribution of the emitted wave. The effect of such interference on monopulse direction finders, which are widely used in weapon control radars, leads to abnormal coordinate determination errors. In some cases, combined jamming methods, the detection of such a jammer is a difficult task. The implementation of a set of measures to protect our own weapon control radars from electronic jamming is a critically important task. It is important to study the errors that occur and to form signs based on which it is possible to select sources of coherent interference. Goal. Evaluation of errors occurring in a monopulse direction finding system and investigation of polarization difference arising from the formation of coherent interference. Results. An assessment of the effect of coherent interference on the direction finding system has been carried out. Based on the calculation, a conclusion was made about the occurrence of an angular direction finding error, which in the range of 2-7 GHz exceeds the accuracy of modern radars. An electrodynamic simulation of the field in the far zone was carried out with radiation of the EA–18G Growler in the microwave CAD. The analysis of the influence of airframe elements on the distribution of the directional pattern is carried out. An assessment of polarization difference in the formation of coherent interference by AN/ALQ-99 aircraft stations has been carried out. It was concluded that there were significant differences in polarization characteristics within two beamwidths for AN/ALQ–99F jammers. Practical significance. Electronic protection against coherent interference generated by an electronic warfare aircraft station is possible on the basis of polarization selection.

HHG light source with polarization selectivity and sub-100-μm beam size for TrARPES

HHG light source with polarization selectivity and sub-100-μm beam size for TrARPES

Theory of acoustic-phonon involved exciton spin flip in perovskite semiconductors

We present a theory of the acoustic phonon assisted spin-flip Raman scattering (SFRS), or resonant photoluminescence with the spin flip of a photoexcited exciton localized in a bulk cubic-phase perovskite semiconductor. We consider the spin-flip transitions between the ground-state exciton spin sublevels in external magnetic field B and discuss the variation of their probability rate and polarization selection rules with the increase of B. The transitions are treated as two-quantum processes with the virtual to and fro transfer of the electron in the electron-hole pair between the bottom and first excited conduction bands. The transfer occurs due to both the electron-hole exchange interaction and the electron-phonon interaction. The theoretical results allow one to distinguish the phonon assisted Raman scattering from (a) the resonant Raman scattering with the combined spin flip of the localized resident electron and hole and (b) the biexciton-mediated SFRS analyzed previously.

Multifunctional beam modulation based on gratings combined with additive metasurfaces

A design scheme combining grating and element additive metasurface is proposed in this paper. Multi-dimensional joint control of the phase, amplitude, angle and polarization and multi-functional integrated metasurface applications were realized by using the inherent characteristics of the light wave properties (polarization and wavelength). Firstly, suitable structural parameters are obtained based on the reflection response of the unit structure, and a 2-bit encoded metasurface array is constructed by utilizing the combinatorial operation between the unit structure. Combined with the polarization selectivity of the lower grating, the dual-function integration of asymmetric transmission (the contrast ratio is 98%) and abnormal reflections (operating bandwidth is 300 nm) was realized. Next, two new half-wave plates were obtained by addition and rotating the elemental structure, and the polarization conversion efficiency of 95%–97% was achieved thanks to the Fabry–Perot cavity formed by the upper metasurface and lower grating. Finally, encoded metasurface based on the geometric phase principle to achieve 300 nm bandwidth cross-polarized wave deflection characteristics with polarization conversion efficiency close to 100%. Our work combines grating structures with element additive metasurfaces, which solves the problem that element structure needs to be redesigned with the change of function, and also paves the way for the application of multifunctional integrated metasurfaces in optical sensing, optical imaging and other fields.

Information encryption driven by strength-switchable circular dichroism in vanadium dioxide based chiral metasurfaces

Switchable polarization selectivity in reconfigurable metasurfaces is highly required in the field of information encryption. In this paper, we proposed a scheme of information encryption by using the giant and strength-switchable circular dichroism (CD) in VO2-based chiral metasurfaces in the mid-infrared region. A bar code information is encrypted and hidden into a VO2-based bielliptic cylinder (BC) and bielliptic cylinder enantiomer (BCE) constructed array. The metallic VO2-based BC and BCE arrays with the rotation angles (α=±14°) exhibit opposite CD (−0.94/0.94) at 6330 nm. With the VO2 transition from metallic to insulator phase, the giant polarization selectivity of both BC and BCE arrays will disappear. Hence, only when the specific environment temperature (>68 °C) and polarization state of incident light (LCP) are simultaneously satisfied, the secret information could be decrypted. The reversible CD in VO2-based chiral metasurfaces possesses great potentials for the application of optical information encryption.

Strong Linearly Polarized Light Emission by Coupling Out-of-Plane Exciton to Anisotropic Gap Plasmon Nanocavity.

With exceptional quantum confinement, 2D monolayer semiconductors support a strong excitonic effect, making them an ideal platform for exploring light-matter interactions and as building blocks for novel optoelectronic devices. Different from the well-known in-plane excitons in transition metal dichalcogenides (TMD), the out-of-plane excitons in indium selenide (InSe) usually show weak emission, which limits their applications as light sources. Here, by embedding InSe in an anisotropic gap plasmon nanocavity, we have realized plasmon-enhanced linearly polarized photoluminescence with an anisotropic ratio up to ∼140, corresponding to degree of polarization (DoP) of ∼98.6%. Such polarization selectivity, originating from the polarization-dependent plasmonic enhancement supported by the "nanowire-on-mirror" nanocavity, can be well tuned by the InSe thickness. Moreover, we have also realized an InSe-based light-emitting diode with polarized electroluminescence. Our research highlights the role of excitonic dipole orientation in designing nanophotonic devices and paves the way for developing InSe-based optoelectronic devices with polarization control.

Electrically Active Terahertz Liquid‐Crystal Metasurface for Polarization Vortex Beam Switching

AbstractPolarized vortex waves have attracted widespread attention in investigations of light–matter interactions and the augmentation of information capacity owing to their distinctive characteristics. Nevertheless, the reconfigurable generation of vector beams, especially at terahertz (THz) frequencies, remains challenging. In this study, a tunable THz polarization vortex beam generator based on a liquid‐crystal metasurface is proposed. A unit cell featuring reconfigurable linear polarization selectivity is developed. A general methodology for designing metasurfaces to generate customized and reconfigurable polarization patterns is introduced. Furthermore, the electrically tunable generation of polarized patterns and cylinder vector beams is experimentally demonstrated. The findings of this study can open up opportunities for wireless communication and super‐resolution imaging applications.

Theoretical analysis of perturbative high harmonic wave mixing from plasma surfaces

High harmonic generation modulated by a weakly perturbing laser field enables new wave mixing frequency components, thus allowing in-situ spatiotemporal measurements and wavefront control of attosecond optical pulses. However, perturbative high harmonic wave mixing from plasma surfaces has not been investigated extensively. In this study, we theoretically analyze the plasma high harmonic generation process in the relativistic regime modulated by a perturbing laser field with an arbitrary frequency. New wave mixing frequency components satisfying the conservation laws of photon energy and momentum are observed. The wave mixing component intensities adhere to a power law for the perturbating laser photon number as the perturbing laser intensity increases, thereby revealing perturbative behaviors in the nonperturbative, extremely nonlinear optical process of high harmonic generation. Detailed studies reveal the polarization selection rule and physical mechanism of high harmonic wave mixing. The modulation of the relativistic factor or mass enhancement of electrons on the plasma surface by the perturbing laser field is believed to result in high harmonic wave mixing in the relativistic regime.

Multifunctional metalens optical tweezers for optical information recognition.

Traditional optical information recognition (OIR), particle capture and manipulation require many optical devices or mechanical moving system components to achieve a specific function, which is difficult to achieve integration. This paper proposes a new method to realize these functions by using multi-focus metalens combining spectrum and polarization selection. The design incorporates three spectral bands, namely 500 nm, 580 nm, and 660 nm, within the visible light range. Additionally, it utilizes either left-handed or right-handed circularly polarized (LCP/RCP) light, resulting in six distinct focus focusing effects on a single focal plane. By analyzing the normalized light intensity (NLI) at the corresponding focus position, the OIR of any wavelength and polarization detection in the design can be realized, and the particle capture at different focusing positions can be realized. Our work can provide a new idea for the high integration of on-chip light recognition and operation and inspire the design of a highly integrated optical system with a smaller size and more substantial function.

RADAR-BASED DETECTION AND RECOGNITION METHODOLOGY OF AUTONOMOUS SURFACE VEHICLES IN CHALLENGING MARINE ENVIRONMENT

This paper presents a methodology that combines radar polarization selection and recognition techniques for navigating objects in atmospheric formations, with a special focus on unmanned surface vehicles (ASVs). The proposed technique utilizes the concept of an energy dissipation matrix to represent these objects as characteristic “shiny dots”. By strategically changing the polarization of the emitted and received electromagnetic waves, the resulting echo energy dissipation matrix is determined. This approach allows the formation of an intensity-based repository of atmospheric formations, which gives SRPC a complete set of tools to account for atmospheric conditions in radar identification of remote objects, including ASVs. The practical application of this technique extends to the improvement of a distinct class of shipborne radar systems optimized for ASVs and their specific navigation requirements. Ultimately, this technology bridges the gap between advanced radar technology and the emerging field of unmanned ground vehicles, providing safer and more proficient navigation in challenging weather conditions.

Colorful multi-plane augmented reality display with dynamically tunable reflective Pancharatnam-Berry phase lens.

Reflective cholesteric liquid crystal (CLC) Pancharatnam-Berry phase lens (PBL) devices have attracted significant attention in augmented reality (AR) display due to their wide spectral and angular response bandwidths, high diffraction efficiency, and polarization selectivity. However, currently reported CLC reflective PBLs are either limited by monochrome display or suffers from complicated design for colorful display. Herein, we demonstrate a colorful multi-plane AR display system with dynamically tunable reflective PBL. The reflective PBL is fabricated by polymer-stabilized cholesteric liquid crystal (PSCLC) that provides dynamical and continuous tunability of color and focal length by direct current (DC) voltage. A proof-of-concept colorful multi-plane AR device is demonstrated, where over 90% diffraction efficiency at desired wavelength has been obtained. The proposed simple, compact, and light AR display system capable of color-imaging with multi-depth shows great application potential in the vehicle-mounted head-up display (HUD).

Silicon Nitride Bent Asymmetric Coupled Waveguides with Partial Euler Bends

Waveguide geometries combining bent asymmetric coupled structures and adiabatic transitions shaped as partial Euler bends are put forward and theoretically analyzed in this work. Designs aiming to reduce the radiation loss, with application in curved waveguide sections and Q-enhanced microresonators, and polarization selection geometries, both for the silicon nitride platform, are studied using highly accurate numerical techniques.

Towards spin state tailoring of charged excitons in InGaAs quantum dots using oblique magnetic fields

We investigate the effect of oblique magnetic field configurations on a singly charged self-assembled quantum dot system as a means to tune the spin composition of the ground electron spin eigenstates. Using magneto-optical spectroscopy and Stokes polarimetry techniques, we evaluate the anisotropic g factors and characterize the polarization properties of the charged quantum dot system under oblique fields. We compare the results to a simple model that captures the resulting level structure and polarization selection rules for arbitrary magnetic field orientations. Under oblique magnetic fields, the system's ground spin eigenstates are composed of unequal superpositions of the electron spins. This provides an additional degree of freedom to tailor the composition of the ground spin states in charged quantum dots and based on this we demonstrate spin pumping and initialization of the tailored ground states, confirming that the double-Λ level structure of the charged quantum dot persists in oblique magnetic fields. These combined results show that the uneven weightings of the tailored spin states can yield systems with interesting behaviors, with a potential towards developing spin-selective readout schemes to further enhance the capabilities of spin qubits. Published by the American Physical Society 2024

Particle Swarm Optimization of Multilayer Multi-Sized Metamaterial Absorber for Long-Wave Infrared Polarimetric Imaging.

Infrared polarization imaging holds significant promise for enhancing target recognition in both civil and defense applications. The Division of Focal Plane (DoFP) scheme has emerged as a leading technology in the field of infrared polarization imaging due to its compact design and absence of moving parts. However, traditional DoFP solutions primarily rely on micro-polarizer arrays, necessitating precise alignment with the focal plane array and leading to challenges in alignment and the introduction of optical crosstalk. Recent research has sought to augment the performance of infrared detectors and enable polarization and spectral selection by integrating metamaterial absorbers with the pixels of the detector. Nevertheless, the results reported so far exhibit shortcomings, including low polarization absorption rates and inadequate polarization extinction ratios. Furthermore, there is a need for a comprehensive figure of merit to systematically assess the performance of polarization-selective thermal detectors. In this study, we employ the particle swarm optimization algorithm to present a multilayer, multi-sized metamaterial absorber capable of achieving a remarkable polarization-selective absorption rate of up to 87.2% across the 8-14 μm spectral range. Moreover, we attain a polarization extinction ratio of 38.51. To elucidate and predict the resonant wavelengths of the structure, we propose a modified equivalent circuit model. Our analysis employs optical impedance matching to unveil the underlying mechanisms responsible for the high absorption. We also introduce a comprehensive figure of merit to assess the efficacy of infrared polarization detection through the integration of metamaterials with microbolometers. Finally, drawing on the proposed figure of merit, we suggest future directions for improving integrated metamaterial absorber designs, with the potential to advance practical mid-infrared polarization imaging technologies.

Assessment of implicit adaptive mesh‐free CFD modelling

SummaryThis work presents details and assesses implicit and adaptive mesh‐free CFD modelling approaches, to alleviate laborious mesh generation in modern CFD processes. A weighted‐least‐squares‐based, mesh‐free, discretisation scheme was first derived for the compressible RANS equations, and the implicit dual‐time stepping was adopted for improved stability and convergence. A novel weight balancing concept was introduced to improve the mesh‐free modelling on highly irregular point clouds. Automatic point cloud generations based on strand and level‐set points were also discussed. A novel, polar selection approach, was also introduced to establish high‐quality point collocations. The spatial accuracy and convergence properties were validated using 2D and 3D benchmark cases. The impact of irregular point clouds and various point collocation search methods were evaluated in detail. The proposed weight balancing and the polar selection approaches were found capable of improving the mesh‐free modelling on highly irregular point clouds. The mesh‐free flexibility was then exploited for adaptive modelling. Various adaptation strategies were assessed using simulations of an isentropic vortex, combining different point refinement mechanisms and collocation search methods. The mesh‐free modelling was then successfully applied to transonic aerofoil simulations with automated point generation. A weighted pressure gradient metric prioritising high gradient regions with large point sizes was introduced to drive the adaptation. The mesh‐free adaptation was found to effectively improve the shock resolution. The results highlight the potential of mesh‐free methods in alleviating the meshing bottleneck in modern CFD.