Linearly Polarized Research Articles

PEM electrolysis: Degradation study of N1110 assemblies for the production of green hydrogen

The production of hydrogen through proton exchange membrane water electrolysis (PEMWE) is seen as a key solution for sustainable energy generation. However, the durability and stability of Proton Exchange Membrane (PEM) cells components, particularly Membrane-Electrode Assemblies (MEAs), remain crucial challenges to overcome for scalability. In this study, the degradation of a 25 cm2 CCM-type MEA was systematically investigated, using N1110 as the polymeric electrolyte and an anodic and cathodic loading of 3 mg/cm2 of PtB. A PEM electrolysis test bench was subjected to controlled operating conditions corresponding to 2 V and 60 °C for two stages of 168 h each, conducting a detailed analysis of performance behavior before, during, and after each degradation period. Electrochemical techniques were employed to characterize the performance stability: chronoamperometry, linear polarization curves, and electrochemical impedance spectroscopy (EIS). The EIS experimental results were fitted to equivalent electrical circuits and the parameters corresponding to ohmic resistances, charge transfer, and diffusional processes were determined. An increase in the resulting time constants and ohmic resistance was depicted because of the degradation.After a straightforward treatment rinsing the assembly with a 1 mol/L H2SO4 solution, the MEA partially regained its initial performance, depicting a degradation rate six times slower than one observed before regeneration in acidic media. This point suggests that the temporary decline in performance of the MEA is primarily due to reversible contamination.

Exploring spin current and dielectric switching characteristics of doped-multiferroic in hexagonal phase for advance RAM technology: A theoretical study

The single-phase bismuth ferrite BiFeO3 (BFO) has garnered significant interest due to its spintronic-based switching properties observed at room temperature. The first-principles calculations were executed to examine the spin-polarized electronic, dielectric, and structural characteristics of co-doped BFO with lanthanum (La) at A-site and cobalt (Co), nickel (Ni) at B-site in its hexagonal phase (Bi1-αLaαFe1-βNiβO3 with α = β = 0.04) with generalized gradient approximation (GGA-PBE). The highest value (1.01 × 10−11 A) of total current observed in La Ni co-doped BFO, featuring a distinct spin current of the same magnitude, attributed to spin polarization at the Fermi level (100 %). Additionally, Co-doped BFO exhibits the highest observed spin current density (1.05 × 109A/m2) and charge current density (1.03 × 10−5A/m2). In case of dielectric switching properties, the Ni-doped BFO displays the lowest values of linear dielectric polarization (6.00 × 10−2 C/m2), polarization charge at its interface (1.27 × 10−17 C), capacitance (4.23 × 10−15 F), and switching energy (3.81 × 10−19 J), which is particularly lower than the reported switching energy (1.92 aJ) of multiferroic capacitor.

Molecular Orientation-Dependent Photonic Polarization Engineering in Organic Single-Crystal-Filled Microcavities.

Designing the polarization degree of freedom of light is crucial in many fields and has widespread application in, for example, all-optical circuits. In this work, we find that in an organic microcavity filled with anisotropic single crystals the cavity modes can be modulated to be elliptically polarized, i.e., partially circularly polarized and partially linearly polarized. The circular polarization component originates from the Rashba-Dresselhaus spin splitting, while the linear polarization component is due to the dislocation of linearly polarized modes. The dislocation of the linear polarizations is ascribed to the orientation of individual molecules and the molecular packing arrangement; hence, the linear polarizations can be controlled by properly structuring the molecular distributions. Our results pave the way for enriching and engineering the polarization properties of individual optical cavity modes in organic microstructures, which may favor the development of polarized lasers with various polarizations.

VCSELs with Stable Linear Polarization Emission Induced by Dielectric Columnar Thin Film Mirrors

VCSELs with Stable Linear Polarization Emission Induced by Dielectric Columnar Thin Film Mirrors

Evolution of C-point singularities and polarization coverage of Poincaré–Bessel beam in self-healing process

As a vector version of scalar Bessel beams, Poincaré–Bessel beams (PBBs) have attracted a great deal of attention due to their non-diffracting and self-healing properties as well as the presence of polarization singularities. Previous studies of PBBs have focused on cases that consist of a superposition of Bessel beams in orthogonal circular polarization states; here, we present a theoretical and experimental study of PBBs for which the polarization states are taken to be linear, which we call a linear PBB. Using a mode transformation of a full Poincaré beam constructed from linear polarization states, we observe the linear PBB as providing an in-principle infinite number of covers of the Poincaré sphere in the transverse plane and with an infinite number of C-points with positive and negative topological indices. We also study the dynamics of C-point singularities in a linear PBB in the process of self-healing after being obstructed by an obstacle, providing insight into “Hilbert Hotel” style evolution of singularities in light beams. The present study can be useful for imaging in the presence of depolarizing surroundings, studying turbulent atmospheric channels, and exploring the rich mathematical concepts of transfinite numbers.

Quarter-wave Pancharatnam-Berry phase gradient liquid crystal-enabled dual-polarization optical edge detection.

Here, we present a novel, to the best of our knowledge, optical edge detection scheme that can be operated in both linear and circular polarization modes, leveraging an optical spatial differentiator constructed by quarter-wave Pancharatnam-Berry (P-B) phase gradient element. After explaining the theoretical mechanism, we utilize a quarter-wave P-B phase liquid crystal polarization grating to validate the dual-polarization optical edge detection capability. We demonstrate that the orientation of linear polarization and the spin of circular polarization dictate the transition between edge and bright-field images. Besides, the linear and circular polarization modes exhibit broadband and monochromatic responsive properties, respectively. This mechanism, dependent on wavelength and polarization, holds promise for applications in color image processing, chiral sensing imaging, and polarization-entangled quantum imaging.

Solar disk integration polarimeter: An automated disk‐integration full‐Stokes‐vector solar feed for the Potsdam Echelle Polarimetric and Spectroscopic Instrument spectrograph

AbstractWe introduce a new solar feed for the PEPSI nighttime spectrograph of the LBT. It enables spectroscopy of the Sun‐as‐a‐star in circular polarization (CP) and linear polarization (LP) with a spectral resolution of 250,000 (≈0.025Å or ) for the wavelength range 383–907 nm. The polarimeter is a dual‐beam design with a modified Wollaston prism as beam splitter and linear polarizer combined with a retractable super‐achromatic retarder. The Wollaston beam diameter is 14 mm and large enough that it does not require a classical telescopic feed anymore. Both polarimetric beams are re‐imaged into respective integration spheres from which two fibers feed the scrambled light to the spectrograph. The system is fully automated in the sense that it finds the Sun in the morning, closes the guider loop, observes a predefined number of individual spectra, and moves to a home position at the end of the day. Among the scientific aims is Zeeman–Doppler imaging of the Sun as a star over the next activity cycle. Our first‐light application detects a clear Stokes‐V/I profile with a full amplitude of on, for example, October 13, 2023, suggesting a solar disk‐averaged line‐of‐sight net magnetic field of +0.37±0.02 G. Comparison of this value with a contemporary full‐disk line‐of‐sight magnetogram suggests an unsigned mean field of about ≈13 G.

Emergence of Optical Anisotropy in Moiré Superlattice via Heterointerface Engineering.

The interaction between light and moiré superlattices presents a platform for exploring unique light-matter phenomena. Tailoring these optical properties holds immense potential for advancing the utilization of moiré superlattices in photonics, optoelectronics, and valleytronics. However, the control of the optical polarization state in moiré superlattices, particularly in the presence of moiré effects, remains elusive. Here, we unveil the emergence of optical anisotropy in moiré superlattices by constructing twisted WSe2/WSe2/SiP heterostructures. We report a linear polarization degree of ∼70% for moiré excitons, attributed to the spatially nonuniform charge distribution, corroborated by first-principles calculations. Furthermore, we demonstrate the modulation of this linear polarization state via the application of a magnetic field, resulting in polarization angle rotation and a magnetic-field-dependent linear polarization degree, influenced by valley coherence and moiré potential effects. Our findings demonstrate an efficient strategy for tuning the optical polarization state of moiré superlattices using heterointerface engineering.

Influence of Post-Heat Treatment on Corrosion Behaviour of Additively Manufactured CuSn10 by Laser Powder Bed Fusion.

This study investigates the influence of heat treatments on the corrosion behaviour of CuSn10 tin bronze, additively manufactured using Laser Powder Bed Fusion (LPBF). LPBF enables the creation of finely structured, anisotropic microstructures, whose corrosion behaviour is not yet well understood. After production, specimens were heat-treated at 320 °C, 650 °C, and in a two-stage treatment at 800 °C and 400 °C, followed by hardness and microstructure analysis. Corrosion tests were conducted using linear polarisation, salt spray, and immersion tests. The results show that heat treatments at 320 °C and 650 °C have no significant effect on the corrosion rate, while the two-stage treatment shows a slight improvement in corrosion resistance. Differences in microstructure and hardness were observed, with higher treatment temperatures leading to grain growth and tin precipitates. The formation of a passive protective layer was detected after 30 h of OCP measurement. Results from other studies on corrosion behaviour were partially reproducible. Differences could be attributed to varying chemical compositions and manufacturing parameters. These findings contribute to the understanding of the effects of heat treatments on the corrosion resistance of additively manufactured tin bronze and provide important insights for future applications in corrosive environments.

Effect of forming parameters on the corrosion performance of retrogression- and warm-formed AA7075 alloy sheets

ABSTRACT Retrogression forming (RF) and warm forming (WF) are used to remedy formability limitations of high-strength precipitation-hardened AA7075 alloy sheets. RF is a thermomechanical treatment combining retrogression heat treatment and the forming of initially peak-aged T6 temper. WF is a thermomechanical treatment of initially pre-aged temper. The present work examines the corrosion performance of retrogression- and warm-formed AA7075 alloy sheets by determining the optimal pre-aging temperature (80°C or 100°C), forming temperature (room temperature, 150–200°C), strain rate (1, 0.1, or 0.01 s−1), and heating rate (1.1 or 20°C·s−1) for conventional slow and novel fast-forming technologies. Several alternating- and direct-current electrochemical tests were administered, including electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization resistance. Results showed that the corrosion performance (i.e., passive film and corrosion-resistant properties) of formed AA7075 sheets was directly proportional to pre-aging and WF temperatures, inversely proportional to the RF temperature, and mildly affected by strain/forming rate and heating rate during forming.

The role of oxidants in the intensive cyanidation of gold. 1. Gold dissolution

In the intensive cyanidation of gravity gold concentrates, sodium m-nitrobenzene sulfonate (NBS) is often used to supplement dissolved oxygen as the oxidant in the process. This paper presents the results of a largely electrochemical study of the behaviour of NBS during cyanidation. The results have confirmed that NBS acts as an oxidant in the cyanidation of gold and that the mixed potential model can be applied to describe the mechanism of its action.The mixed potential is a good initial indicator of the rate of gold dissolution and, as expected, the anodic dissolution of pure gold in cyanide solutions is characterized by passivation at potentials above about −0.35 V.The reduction of oxygen under the conditions of the present study occurs in two 2-electron steps with peroxide as an intermediate. Dissolution of gold occurs at potentials in the diffusion-controlled region for the first step. The cathodic reduction of NBS occurs in the same potential region as the reduction of oxygen. The reaction is first order in the concentration of NBS and is largely independent of the pH. The stoichiometry of the reaction involves six moles of gold per mole of NBS confirming that the amine is the final product of reduction of NBS.Rates of gold dissolution in various solutions have been measured using a calibrated linear polarisation method. The rate increases approximately linearly with increasing NBS concentration and is independent of pH. The rate in 0.5 g/L NBS is approximately the same as in oxygenated solutions.A relatively simple titration has been adapted for use in determining NBS concentrations.

Reflection–Polarization Characteristics of Greenhouses Studied by Drone-Polarimetry Focusing on Polarized Light Pollution of Glass Surfaces

Drone-based imaging polarimetry is a valuable new tool for the remote sensing of the polarization characteristics of the Earth’s surface. After briefly reviewing two earlier drone-polarimetric studies, we present here the results of our drone-polarimetric campaigns, in which we measured the reflection–polarization patterns of greenhouses. From the measured patterns of the degree and angle of linear polarization of reflected light, we calculated the measure (plp) of polarized light pollution of glass surfaces. The knowledge of polarized light pollution is important for aquatic insect ecology, since polarotactic aquatic insects are the endangered victims of artificial horizontally polarized light sources. We found that the so-called Palm House of a botanical garden has only a low polarized light pollution, 3.6% ≤ plp ≤ 13.7%, while the greenhouses with tilted roofs are strongly polarized-light-polluting, with 24.8% ≤ plp ≤ 40.4%. Similarly, other tilted-roofed greenhouses contain very high polarized light pollution, plp ≤ 76.7%. Under overcast skies, the polarization patterns and plp values of greenhouses practically only depend on the direction of view relative to the glass surfaces, as the rotationally invariant diffuse cloud light is the only light source. However, under cloudless skies, the polarization patterns of glass surfaces significantly depend on the azimuth direction of view and its angle relative to the solar meridian because, in this case, sunlight is the dominant light source, rather than the sky. In the case of a given direction of view, those glass surfaces are the strongest polarized-light-polluting, from which sunlight and/or skylight is reflected at or near Brewster’s angle in a nearly vertical plane, i.e., with directions of polarization close to horizontal. Therefore, the plp value is usually greatest when the sun shines directly or from behind. The plp value of greenhouses is always the smallest in the green spectral range due to the green plants under the glass.

Photon Emission by an Electron in a Constant Background Field Modeling a Lorentz-Noninvariant Vacuum

Abstract We considered the radiative transition of an electron due to its spin-flip in a constant background field of the quasielectric type, which models the Lorentz-noninvariant vacuum. The power and probability of radiation and the degree of its linear polarization are calculated. It is shown that this radiative transition leads to the complete polarization of the initially unpolarized electron beam. The investigated effects increase with increasing electron energy.

Ultra-broadband and thin switchable multifunctional metamaterial for terahertz wave

An ultra-broadband thin multi-functional and switchable metamaterial is examined in the terahertz (THz) regime. The proposed design achieved high polarization conversion efficiency and can be switched from a polarization converter to an absorber using the phase change transitioning of vanadium dioxide (VO2). The linear polarization conversion is achieved from 6.0 THz to 15.0 THz, achieving a bandwidth of 9.0 THz, and the absorption is realized from 5.0 THz to 16.0 THz with a bandwidth of 11.0 THz. These broadband characteristics were achieved by a simple metamaterial design incorporating a few layers. The relative bandwidth was 85% for the polarization conversion and 105% for the absorption. Moreover, the angular stability of the designed structure is impressive for various incident angles from 0° to 45°. The proposed switchable design has the potential to contribute to the development of tunable polarization rotating devices, on/off switching LPC devices, which have wide application potentials in THz detection, sensing, adaptive optics, and communications.

Short-length nanosecond pulsed 1.653-μm DBR fiber Raman laser oscillator fabricated by femtosecond laser direct-writing

We demonstrate a nanosecond pulsed 1.653-μm fiber Raman laser (FRL) oscillator in a short-length distributed Bragg reflector (DBR) cavity made by femtosecond laser direct-writing technique. The DBR FRL cavity is composed of commercial ultrahigh NA germanium-doped silica fiber with a short length of 10 m and a pair of fiber Bragg gratings (FBGs). The FBGs were directly inscribed on the ends of the Raman gain fiber, using femtosecond-laser point-by-point (PbP) writing method. A home-made 1.55-μm nanosecond fiber laser source was used as the pump of the FRL. 1.653-μm nanosecond pulsed laser oscillation with maximum average output power of 125 mW (corresponding to peak power of 6.6 W), 3 dB linewidth of ≤ 0.15 nm, and slope efficiency of 48 % was obtained under 1.55-μm pump with optimized repetition rate of 10 MHz. The optical signal-to-noise-ratio (OSNR) of the 1.653-μm narrow-linewidth Raman lasing is above 70 dB. The short-length DBR FRL output exhibits decently high degree of polarization (DOP) and high degree of linear polarization (DOLP) above 80 % in 3-hour period, benefitted from the birefringent FBGs made by femtosecond laser direct-writing method. It is expected that by further reducing the cavity length to < 1 m, the 1.653-μm DBR FRL oscillator made by femtosecond laser direct-writing method is promising as single-frequency narrow-linewidth, highly linearly polarized, high-OSNR laser sources for high-sensitivity CH4 gas detection.

Fermionic signal of vacuum polarization in strong laser fields

Vacuum polarization (VP) is investigated for the interaction of a polarized γ-ray beam of GeV photons with a counterpropagating ultraintense laser pulse. In a conventional setup of a vacuum birefringence measurement, a VP signal is the emerging small circular (linear) polarization of the initially linearly (circularly) polarized probe photons. The pair production via the nonlinear Breit-Wheeler process in such a high-energy environment eliminates part of the γ photons in the outgoing γ beam, increasing the statistical error and decreasing the accuracy of this VP signal. In contrast, we investigate the conversion of the emerging circular polarization of γ photons into longitudinal polarization of the created positrons, considering the latter as the main VP signal. To study the VP effects in the highly nonlinear regime, where the Euler-Heisenberg effective Lagrangian method breaks down, we have developed a Monte Carlo simulation method, incorporating vacuum birefringence and dichroism via the one-loop QED probabilities in the locally constant field approximation. Our Monte Carlo method will enable the study of VP effects in strong fields of arbitrary configuration. With 10 PW laser systems, we demonstrate the feasibility of detecting the fermionic signal of the VP effect at the 5σ confidence level with a few hours of measurement time. Published by the American Physical Society 2024

Dynamic reversal of Fano response of metagratings by rotation of linear polarization

Dynamic reversal of Fano response of metagratings by rotation of linear polarization

Impacts of corrosion inhibiting admixture and supplementary cementitious material on early strength concrete

This research aimed to evaluate the influence of alccofine 1203 on a mineral admixture and sodium nitrite as a corrosion inhibitor on the properties of concrete. To achieve these aims, an experimental investigation was carried out on a set of composite samples comprising five distinct concrete formulations. Five different mixes for the concrete were used as the overlay materials such as NC as a reference concrete, alccofine concrete (i.e. 25% cement replaced with alccofine), and alccofine concrete with varying dosages of sodium nitrite (i.e. 1%, 1.25%, and 1.5%). Alccofine reduced the workability and water absorption and increased the compressive strength of the concrete (5%) at curing age of 28 days. Adding sodium nitrite further reduced water absorption of the concrete and workability but compressive strength of 29.15% and 26.93% for the curing period of 3 and 7 days, respectively. The pH of the concrete powdered solution became more alkaline with the replacement of alccofine and addition of sodium nitrite. Free chloride content dropped by 48 and 66%, respectively, with the introduction of GGBS and sodium nitrite. Corrosion properties of the concrete samples were examined using open circuit potentials and linear polarization resistance of various concrete mixes after being immersed in 1 M H2SO4 and 3% NaCl environment. The findings indicated a notable improvement in the corrosion resistance, water absorption test, thermal conductivity, strength properties, and microstructural properties of concrete with the incorporation of SN in combination with alccofine. The application of the response surface method allowed for the prediction, validation, and optimization of experimental data using a regression equation.

Linearly polarized GaN micro-LED with adjustable directional emission integrated with a continuous metasurface

Traditional LEDs emit light that exhibits incoherence and displays a Lambertian distribution. To achieve linearly polarized (LP) light and control the emission direction, a variety of optical components are required to be stacked, which is unsuitable for compact applications and results in low deflection efficiency. Here, we propose and and numerically simulate a novel single-chip micro-resonant cavity LED (micro-RCLED) device that generates directional LP light by integrating a continuous metasurface. This device includes a bilayer grating at the GaN layer's bottom, providing high transverse electric (TE) reflectivity above 89.5% and an extinction ratio exceeds 57 dB at 500 nm. The top distributed Bragg reflector (DBR) and the bilayer grating together constitute a TE mode Fabry–Pérot resonant cavity. This not only promotes the emission of the TE wave, but also guarantees its collimation with the appropriate phase, thereby enhancing its spatial coherence. A functional metasurface above the DBR layer precisely controls the TE wave's deflection angle. It maintains a low aspect ratio while enabling efficient, large-angle deflection. The simulation results demonstrate that this device provides an effective solution for generating highly spatially coherent directional LP light, with broad potential applications in fields such as polarized light imaging and advanced 3D micro-LED display systems.

Interaction of Hermite–Gaussian Beams with a Macroscopic Atomic Target

AbstractA theoretical analysis is presented on the photoexcitation of a macroscopic atomic target by a Hermite–Gaussian (HG) beam within the framework of density matrix theory. Special emphasis is paid to the influence of the incoming HG mode on the population of an excited state and the emitted fluorescence radiation. In particular, a general expression for the alignment parameter of the excited state is derived, which depends on the beam parameters of the HG mode. Although the developed theory can be applied to any atomic system, here the electric dipole transition in neutral sodium atoms is investigated when driven by three , and modes. For this optical (valence‐shell) excitation, it is demonstrated that the population of the excited state is sensitive to the beam waist and the mode index of the HG beam. Furthermore, the influence of beam parameters on the angular distribution and linear polarization of the emitted fluorescence radiation is discussed.