Polarization Dependence Research Articles

Numerical analyses of a mid-IR metasurface spectral beam combiner with high efficiency and low phase distortion

Mid-infrared lasers have been widely used in chem/bio-sensing, medical diagnostics, environmental monitoring, and defense. These applications frequently require broad spectral coverage, high brightness, and compact size. Spectral beam combining (SBC) technology has been proven to be efficient in scaling laser power and broadening spectral range. Although the blazing grating has been successfully applied as the SBC component in mid and far infrared, its performance is limited by strong dispersion and polarization dependence. In this paper, we proposed a spectral beam combiner based on the dual-band anomalous reflective metasurface. The combiner had ultra-high, polarization-independent anomalous reflectivity in two spectral bands (4.0 μm and 4.6 μm). In both bands, the bandwidth with over 95% reflectivity was 100 nm. These properties made both the dense SBC and two-band SBC possible. Moreover, the impacts of the input laser properties on the combining efficiency and beam quality were thoroughly studied. The metasurface beam combiner exhibited high tolerance to the incident angle deviation and input laser spectral linewidth. Even when the laser has a broad linewidth of 70 nm incident on the beam combiner with a large angle deviation of 10°, the beam combiner still showed a higher than 90% efficiency and good reflective beam quality M2<1.5. In addition, in the dense SBC situation, when 7 individual lasers with a central wavelength interval of 25 nm were combined the beam propagation parameter M2 was better than 1.5. We believe that the metasurface spectral beam combiner was an effective alternative to the commercial diffractive gratings and was capable of combining multiple beams from broadband laser sources.

Nonlinear Breit–Wheeler pair production using polarized photons from inverse compton scattering

Abstract Observing multiphoton electron–positron pair production (the nonlinear Breit–Wheeler process) requires high-energy γ rays to interact with strong electromagnetic fields. In order for these observations to be as precise as possible, the γ rays would ideally be both mono-energetic and highly polarized. Here we perform Monte Carlo simulations of an experimental configuration that accomplishes this in two stages. First, a multi-GeV electron beam interacts with a moderately intense laser pulse to produce a bright, highly polarized beam of γ rays by inverse Compton scattering. Second, after removing the primary electrons, these γ rays collide with another, more intense, laser pulse in order to produce pairs. We show that it is possible to measure the γ-ray polarization dependence of the nonlinear Breit–Wheeler process in near-term experiments, using a 100 TW class laser and currently available electron beams. Furthermore, it would also be possible to observe harmonic structure and the perturbative-to-nonperturbative transition if such a laser were colocated with a future linear collider.

Innovative Approach to Achieving Polarization Dependent Highly Directional Nanolasers Through Propagating States in Diverse Plasmonic Lattices.

With their extremely small mode volumes, excellent field enhancement, and low radiative loss, metallic nanoparticle arrays supporting plasmonic lattice resonances have emerged as a potential design for on-chip plasmonic lasers. Due to the similarities between photonic crystals and plasmonic lattices in terms of structural features and energy band structure, the properties of plasmonic lattice-based nanolasers, including low threshold, lasing wavelength, coherence, directionality, and polarization, can be designed using band structure computations. Here 2D plasmonic lattices of Al nanocone arrays (NCAs) are presented, supporting narrow linewidth resonances that provide optical feedback for the stimulated emission process of optically pumped Rhodamine 6G (R6G). Remarkably, highly directional nanoscale lasing with polarization dependence at red-light wavelengths is presented by the artificially predesigned plasmonic band structure at the propagating state with different lattice symmetries and enables effective coupling with quantum emitters at various wavelengths. Furthermore, the lasing dynamics in these structures are also investigated, employing a dynamic semi-quantum approach that considers both stimulated and spontaneous emission. These findings broaden the lasing characteristics diversity in plasmonic nanoparticle arrays and provide a simple framework for presenting promising prospects for the management and operation of on-chip nanoscale laser sources.

Polarization-independent full-color holographic movie with a single metasurface free from crosstalk.

Metasurface holograms offer advantages, such as a wide viewing angle, compact size, and high resolution. However, projecting a full-color movie using a single hologram without polarization dependence has remained challenging. Here, we report a full-color dielectric metasurface holographic movie with a resolution of 512 × 512. Eight frames were multiplexed across blue (445 nm), green (532 nm), and red (633 nm) color channels, achieving a maximum reconstruction rate of 5.6 frames per second. The superposition of the three wavelengths was achieved by adjusting the resolution and position of each target image while maintaining a constant pitch of the meta-atoms. Additionally, we identified the positions of crosstalk images generated that occur due to fabrication errors and proposed and demonstrated conditions and corrections to ensure they do not overlap with the intended images. The superimposition of phase distributions for each wavelength was achieved using the least squares error method, based on a library of over 20,000 types of meta-atoms. These results are anticipated to advance the future development of three-dimensional metasurface holographic movies.

Hybrid Hermite-Laguerre-Gaussian vector modes.

Vector modes are well-defined field distributions with spatially varying polarization states, rendering them irreducible to the product of a single spatial mode and a single polarization state. Traditionally, the spatial degree of freedom of vector modes is constructed using two orthogonal modes from the same family. Here, we introduce a novel class of vector modes whose spatial degree of freedom is encoded by combining modes from both the Hermite- and Laguerre-Gaussian families, ensuring that the modes are shape-invariant upon propagation. This superposition is not arbitrary, and we provide a detailed explanation of the methodology employed to achieve it. This new class of vector modes, which we term hybrid Hermite-Laguerre-Gaussian (HHLG) vector modes, gives rise to subsets of modes exhibiting polarization dependence on propagation due to the difference in mode orders between the constituent modes, while remaining eigenmodes of free space. To the best of our knowledge, this is the first demonstration of vector modes composed of two scalar modes originating from different families.

Low-polarization-sensitive 1 × 2 carrier-injection-type silicon photonic switch consisting of input-/ output-side polarization splitter/rotators and a single Mach-Zehnder interferometer.

We propose a low-polarization-sensitive 1 × 2 carrier-injection-type silicon photonic switch consisting of a single Mach-Zehnder interferometer, an input-/output-side polarization splitter and rotators, bidirectional light injection, and an external optical circulator. A polarization-dependent loss (PDL) of 1.3 dB was achieved using the proposed structure, whereas a PDL exceeding 17 dB was observed without the structure. In addition, owing to the large birefringence of the silicon waveguide, a differential group delay (DGD) of 10 ps for a 10 Gbps OOK signal was observed. However, a reduced polarization dependence was confirmed through bit error rate measurements, with the power penalty difference lower than 1 dB.

Tuning electronic and optical properties of 2D polymeric C60 by stacking two layers.

Benefiting from improved stability due to interlayer van der Waals interactions, few-layer fullerene networks are experimentally more accessible compared to monolayer polymeric C60. However, there is a lack of systematic theoretical studies on the material properties of few-layer C60 networks. Here, we compare the structural, electronic and optical properties of bilayer and monolayer fullerene networks. The band gap and band-edge positions remain mostly unchanged after stacking two layers into a bilayer, enabling the bilayer to be almost as efficient a photocatalyst as the monolayer. The effective mass ratio along different directions is varied for conduction band states due to interlayer interactions, leading to enhanced anisotropy in carrier transport. Additionally, stronger exciton absorption is found in the bilayer than that in the monolayer over the entire visible light range, rendering the bilayer a more promising candidate for photovoltaics. Moreoever, the polarisation dependence of optical absorption in the bilayer is increased in the red-yellow light range, offering unique opportunities in photonics and display technologies with tailored optical properties over specific directions. Our study provides strategies to tune electronic and optical properties of 2D polymeric C60via the introduction of stacking degrees of freedom.

Transparent dual‐band wide‐angle polarization‐insensitive single‐layer frequency selective surface for mm‐wave 5G communication systems

AbstractA highly transparent single‐layer frequency selective surface (FSS) with an optical transmittance of 92.7% at 550 nm, designed for 5G communication systems operating in dual frequency bands of 26 and 38 GHz is proposed. The dual‐band FSS not only achieves high optical transparency but also maintains good electrical performance. The transmission performance of the FSS is stable to the polarization and angles of incidence for electromagnetic waves. As a proof of concept, the FSS with periodic square loops patterned on a 188‐µm‐thick substrate is fabricated. Each loop is constructed with metallic mesh electrodes having a pitch of 10 µm. Measurements are conducted using two different systems: a free‐space measurement system and a vector network analyser‐based material characterization kit. After calibrating the measurement systems, the scattering parameters of the fabricated surface are measured. The results obtained from both measurement systems show good agreement and also agree with the simulated results. The designed surface has an insertion loss of less than 3 dB in the dual passband region. The proposed dual‐band FSS has the merits of polarization independence, angular insensitivity, and high transparency.

Substrate, temperature, and magnetic field dependence of electric polarization in mixed-stacking tetralayer graphenes

Polytypes of tetralayer graphene (TLG: Bernal, rhombohedral, and mixed stacking) are crystalline structures with different symmetries. Among those, mixed-stacking tetralayers lack inversion symmetry, which allows for intrinsic spontaneous out-of-plane electrical polarization, inverted in the mirror-image pair, ABCB and ABAC stackings. Here, we compare the intrinsic polarization of such TLGs with the symmetry-breaking effect of a substrate, which can also generate out-of-plane electric dipole moments with different sizes in all four polytypes, including ABCB and ABAC twins. We analyze their temperature and magnetic field dependence, in view of understanding the origin of the recently measured Kelvin probe force microscopy maps of tetralayer flakes [S. S. Atri ], and notice that the intrinsic contribution could be singled out based on magnetic field dependence of polarization measured at low temperatures. Published by the American Physical Society 2024

Multi-Layer Absorber based on Plasmonic Resonances for Photovoltaic Applications at Visible Spectra

This paper introduces a broadband absorber based on a multilayered, double-cylindrical-shaped metamaterial, numerically characterized for its performance. The structure comprises four interacting layers that generate plasmonic resonances. CST microwave simulations were conducted to analyze its absorption characteristics. The results demonstrate that the proposed metamaterial absorber achieves 99% absorption at 847 nm frequency region and 98% absorption in the 500-1200 nm frequency region. Additionally, polarization dependency analysis confirms that the absorber performs as a perfect, polarization-independent absorber across the studied frequency range. It exhibits high absorption in both TE and TM modes and remains unaffected by polarization or variations in the incident angle. Numerical simulations reveal that the absorption performance is driven by a combination of Fabry–Perot resonance effects, localized surface plasmons, and propagating surface plasmons. In summary, the proposed metastructure demonstrates omnidirectional absorption, polarization independence, and wide-angle incident absorption. This design shows significant potential for applications in photodetectors, active optoelectronic devices, and sensors.

Design and Evaluation of a Cloud Computing System for Real-Time Measurements in Polarization-Independent Long-Range DAS Based on Coherent Detection.

CloudSim is a versatile simulation framework for modeling cloud infrastructure components that supports customizable and extensible application provisioning strategies, allowing for the simulation of cloud services. On the other hand, Distributed Acoustic Sensing (DAS) is a ubiquitous technique used for measuring vibrations over an extended region. Data handling in DAS remains an open issue, as many applications need continuous monitoring of a volume of samples whose storage and processing in real time require high-capacity memory and computing resources. We employ the CloudSim tool to design and evaluate a cloud computing scheme for long-range, polarization-independent DAS using coherent detection of Rayleigh backscattering signals and uncover valuable insights on the evolution of the processing times for a diverse range of Virtual Machine (VM) capacities as well as sizes of blocks of processed data. Our analysis demonstrates that the choice of VM significantly impacts computational times in real-time measurements in long-range DAS and that achieving polarization independence introduces minimal processing overheads in the system. Additionally, the increase in the block size of processed samples per cycle results in diminishing increments in overall processing times per batch of new samples added, demonstrating the scalability of cloud computing schemes in long-range DAS and its capability to manage larger datasets efficiently.

Theoretical investigation on excited state intramolecular proton transfer of 5-hydroxy-6,7,4'-trimethoxyflavone: state specific solvation approach versus linear response solvation

Flavonoids are polyphenolic organic compounds with wide range of physical and biological importance. In this article, we aimed to perform detailed structural analysis to predict photophysics of 5-hydroxy-6,7,4'-trimethoxyflavone (5HTMF) in vacuum and different solvents. The ground state optimised structure (S0) computed at DFT/CAM-B3LYP/6-31G(d,p) level, accurately correlates with experimental structure. Excited state (S1) was more polar than ground state (8.20–11.16 Debye in vacuum; 9.68–12.72 Debye in cyclohexane). The computed potential energy curves along proton transfer reaction coordinate showed inoperativeness of ground state intramolecular proton transfer. In sharp contrast, barrierless potential of first excited state confirms occurrence of excited state intramolecular proton transfer phenomenon. The absorption wavelength for S0 → S1 (Frank Condon) transition was within 304–310 nm, in different solvents. The polarity dependency of fluorescence emission for S0 ← S1 transition was negligible as compared to absorption, and significant Stoke’s shift was identified (Δλ = 467–515 nm). All these computational outputs support experimental findings and compared with parent 5-Hydroxy-flavone (5HF) molecule. Substituting three methoxy groups in 5HF shifts fluorescence emission maximum of 5HTMF to near-infrared region, increase enormous applications. Moreover, state-specific solvation method was found a practical, theoretical approach to corroborating experimental findings.

Strong coupling between exciton and quasi-bound state in the continuum with polarization dependence

Exciton–polaritons which are formed by the strong coupling of photon and exciton, have aroused great interest. In this work, we study the strong coupling between the exciton of WS2 monolayer (perovskite) and quasi-bound states in the continuum (QBIC) under y(x) polarization, in the perovskite metasurface with WS2 monolayer. Here, QBIC mode is achieved by introducing the asymmetric parameter. It is found that the energy of Rabi splitting can reach 41.369 meV (235.19 meV) under y-polarization (x-polarization). The dispersion-coupled oscillation model is used to illustrate the strong coupling mechanism. Besides, the influences of the asymmetric parameter and the positions of WS2 monolayer on the Rabi splitting are also discussed, which are verified by finite element method (FEM) simulations. Compared with the previous works, our method provides a way to achieve Rabi splitting with polarization dependence.

Three-dimensional bonding anisotropy of bulk hexagonal metal titanium demonstrated by high harmonic generation

High harmonic generation (HHG) in solid-state materials is an emerging field of photonics research that can unveil the detailed electronic structure of materials, bond strengths and scattering processes of electrons. Although HHG in semiconducting and insulating materials has been intensively investigated both experimentally and theoretically, metals have rarely been explored because the strong screening effect of high-density free electrons is considered to significantly weaken the HHG signal. Here, we investigated HHG upon infrared excitation in bulk hexagonal metal titanium (Ti), a typical building block for practical lightweight structural materials. By analyzing the polarization dependence, the approach revealed the three-dimensional (3D) anisotropy in the electronic states. The results demonstrated the potential of HHG spectroscopy for characterizing 3D bonding anisotropy in metallic systems that are of fundamental importance for designing lightweight and strong structural materials.

The Importance of Catalytic Effects in Hot-Electron-Driven Chemical Reactions.

Hot electrons (HEs) represent out-of-equilibrium carriers that are capable of facilitating reactions which are inaccessible under conventional conditions. Despite the similarity of the HE process to catalysis, optimization strategies such as orbital alignment and adsorption kinetics have not received significant attention in enhancing the HE-driven reaction yield. Here, we investigate catalytic effects in HE-driven reactions using a compositional catalyst modification (CCM) approach. Through a top-down alloying process and systematic characterization, using electrochemical, photodegradation, and ultrafast spectroscopy, we are able to disentangle chemical effects from competing electronic phenomena. Correlation between reactant energetics and the HE reaction yield demonstrates the crucial role of orbital alignment in HE catalytic efficiency. Optimization of this parameter was found to enhance HE reaction efficiency 5-fold, paving the way for tailored design of HE-based catalysts for sustainable chemistry applications. Finally, our study unveils an emergent ordering effect in photocatalytic HE processes that imparts the catalyst with an unexpected polarization dependence.

Chlorinated graphite as positive electrode for aluminium-ion batteries with 1-ethyl-3-methylimidazolium chloride/aluminium chloride electrolyte

The article defines the dependence type of the cathode polarization of an aluminum-ion battery based on chlorinated graphite of the initial EC-02 type in a low-temperature melt of aluminum chloride with 1-ethyl-3-methylimidazole chloride on the geometric characteristics of the electrode and the current density. It is determined that for the chlorinated graphite material the polarization values are slightly reduced compared to the initial non-chlorinated graphite of the same brand in a similar melt and are 25–50 mV at 1 mA/cm2. The dependence of polarization on the current density does not have a break between the values of 1 and 1.2 mA/cm2, observed for initial graphite, which characterizes the maximum rate of the current-generating reaction, which means an increase in the rate of the main process on the chlorinated graphite. Using a reference experiment on a glassy carbon electrode, the surficial density of chloroaluminate complexes intercalation sites was estimated as about 15%. Accordingly, the maximum degree of intercalation for such materials is 6. Since graphite chlorination does not lead to distortions geometric parameters of its interlayer gaps, the sorption density of chloroaluminate ions is found to increase after chlorination; in the case of non-chlorinated graphite, the degree of intercalation varies with current density from 9 to 18.

DFT-based calculation of vibrational sum frequency generation spectral features of crystalline β-sheets in silk: Polarization and azimuth angle dependences.

Sum frequency generation (SFG) necessitates both noncentrosymmetry and coherence over multiple length scales. These requirements make vibrational SFG spectroscopy capable of probing structural information of noncentrosymmetric organic crystals interspersed in polymeric matrices and their three-dimensional spatial distributions within the matrices without spectral interferences from the amorphous components. However, this analysis is not as straightforward as simple vibrational spectroscopy or scattering experiments; it requires knowing the molecular hyperpolarizability of SFG-active vibrational modes and their interplay within the coherence length. This study demonstrates how density function theory (DFT) calculations can be used to construct the molecular hyperpolarizability of a model system and combine it with the SFG theory to predict the polarization and azimuth angle dependences of SFG intensities. A model system with short peptide chains mimicking β-sheet domains in Bombyx mori silk was chosen. SFG signals of the amide-I, II, III, and A bands and one of the CH deformation modes were simulated and compared with the experimental results and the predictions from the group theory. The SFG features of amide-I and A bands of antiparallel β-sheet could be explained with DFT-based theoretical calculations. Although vibrational coupling with neighboring groups breaks the symmetry of the D2 point group, the group theory approach and DFT calculations gave similar results for the amide-I mode. The DFT calculation results for amide-II did not match with experimental data, which suggested vibrational coupling within a larger crystalline domain may dominate the SFG spectral features of these modes. This methodology can be applied to the structural analysis of other biopolymers.

Influence of the AlN-sapphire template on the optical polarization and efficiency of AlGaN-based far-UVC micro LED arrays

Abstract Arrays of far-UVC micro LEDs based on AlGaN and emitting at 233-235 nm have been fabricated on different types of AlN-sapphire templates and the optical polarization, output power, and efficiencies have been studied in dependence of the template technology and the mesa diameter of the micro-pixels. While LEDs fabricated on MOVPE AlN-sapphire templates show dominant TM polarized emission with a degree of polarization of −0.2, LEDs on high temperature annealed AlN-sapphire templates show dominant TE polarized emission with a degree of polarization of 0.2–0.3. The output power and external quantum efficiency increases with decreasing diameter of the slanted and reflective micro LED mesa. Peak output powers of 18 mW at 200 mA and peak external quantum efficiencies of up to 2.7 % for mesa diameters of 1.5 µm on annealed templates were measured, corresponding to peak wall plug efficiencies of 1.7 %, while conventional LEDs with large mesa areas on the same template showed maximum EQEs of 1.1 %. The relative increase in output power by using the micro LED approach as compared to a conventional large area emitter is stronger for LEDs on MOVPE AlN templates than on annealed templates (about a factor of 3.7 vs. 2.3, respectively, at 50 mA) which is attributed to the polarization dependence of the light extraction.

Ultraviolet scattering polarization from space particles entering Earth’s atmosphere

ABSTRACT Space material from leftovers of comets and asteroids is daily entering the Earth’s atmosphere. Traditionally, this influx has been characterized from ground-based observations or through meteorite searches. However, cosmic dust and small meteoroids (below a grain size of 1 cm) are not easily detectable with the current facilities and there is scant information about them. In this work, we analyse the feasibility of characterizing the low-mass end of the dust size distribution using observations at ultraviolet wavelengths from space. For this purpose, we have computed the expected scattered ultraviolet radiation and polarization produced by space dust falling on Earth using the Monte Carlo code radmc-3d. We have built a density model attending to the features and parameters obtained from measurements of meteorites, meteor showers, and cometary dust observations. We show that silicate grains will be easily distinguishable from carbonates and irons based on polarization measurements. Moreover, the polarization reversals produced in the resonance scattering regime can be used to study the details of the size distribution of small dust grains. We point out the dependence of the modelled polarization on the way of discretizing the particle size distribution.

Numerical modeling of thermal dust polarization from aligned grains in the envelope of evolved stars with updated POLARIS

Abstract Magnetic fields are thought to influence the formation and evolution of circumstellar envelopes around evolved stars. Thermal dust polarization from aligned grains is a promising tool for probing magnetic fields and dust properties in these environments; however, a quantitative study on the dependence of thermal dust polarization on the physical properties of dust and magnetic fields for these circumstellar environments is still lacking. In this paper, we first perform the numerical modeling of thermal dust polarization in the IK Tau envelope using the magnetically enhanced radiative torque (MRAT) alignment mechanism implemented in our updated POLARIS code, accounting for the effect of grain drift relative to the gas. Despite experiencing grain drift and high gas density $n_{\rm gas} > 10^6\, \rm cm^{-3}$, the minimum grain size required for efficient MRAT alignment of silicate grains is $\sim 0.007 - 0.05\, \rm \mu m$ due to strong stellar radiation fields. Ordinary paramagnetic grains can achieve perfect alignment by MRAT in the inner envelope of $r < 500\, \rm au$ due to stronger magnetic fields of B ∼ 10 mG - 1G, producing the polarization degree of ∼10 %. The polarization degree can be enhanced to ∼20-40 % for superparamagnetic grains with embedded iron inclusions. The magnetic field geometry affects the resulting polarization degree due to the projection effect. We investigate the effect of rotational disruption by RATs (RAT-D) and find that the RAT-D effect decreases the dust polarization degree due to the decrease in the maximum grain size. Our modeling results motivate further observational studies at far-infrared/sub-millimeter to constrain the properties of magnetic fields and dust in evolved star’s envelopes.