Linearly Polarized Research Articles

Increasing the electric field amplification in the metal-insulator-metal structure with a grating hybrid of bowtie nanotriangle and cylindrical nanodisc

In this paper, the strong electromagnetic coupling between an integrated grating of an array of periodic gold nanodiscs and an array of bowtie nanotriangles placed on layers of a dielectric and a metal has been investigated. The upper layer is periodically created by removing each nanodisk in the array of nanodisks and replacing it with bowtie nanotriangles. The structure for near field radiation with linear polarization at 800nm wavelength is optimized so that it has the highest amount of amplification in the gap space between the tips of the nanotriangle with a minimum value of 188 times and a maximum of 320 times. The simulation results confirm that the huge field enhancement obtained is due to the strong coupling between the LSPR formed in the grating of bowties nano triangle and nanodiscs and the SPPs formed in the metal film. The amount of amplification compared to the array of only nanodiscs (about 32 times) or only bowtie nano triangles (about 120 times) is not only higher, but also the anti-crossing behavior is observed. The high amplification obtained at the mentioned wavelength can be used for laser oscillators with a central wavelength of 800nm, such as titanium sapphire, etc., which has many applications in near-field physics, SERS, and ultrafast lasers.

Characterization of a four-channel surface plasmon polaritons emitter based on a combined grooves coupling structure using photoemission electron microscopy

In various functional devices relying on femtosecond surface plasmon polaritons (SPPs), actively controlling the propagation direction of the SPPs field is crucial for designing plasmon-based functional devices. This capability is particularly valuable in optical logic circuits and optical communication systems. In this study, we employed photoemission electron microscopy (PEEM) to conduct near-field imaging of the SPPs field generated by a novel combination of wide and narrow grooves etched on a flat silver film. Experimental results revealed that femtosecond SPPs fields excited by laser pulses with different linear polarizations (±45°) can be emitted in four distinct directions, showcasing the combined groove structure's potential as a four-channel SPPs emitter. Additionally, Finite-Difference Time-Domain (FDTD) simulations were utilized to model the time evolution envelope of SPPs modes excited by groove coupling structures irradiated with laser pulses of varying polarization directions. The physical mechanism behind the combined groove structures as a four-channel SPPs emitter was thoroughly analyzed, and the experimental findings closely aligned with the FDTD simulation results. This research is of significant importance for advancing novel ultra-fast micro-nano optoelectronic devices with exceptional properties and for constructing ultra-fast information processing systems in plasmonics nanocircuits.

Modal gain characteristics of few-mode erbium-doped fiber amplifiers with pump mode beating

Using the linear polarization (LP) mode decomposition method, we theoretically analyze the beat effect between the same polarization components of the vector pump modes and propose a pump beat model of few-mode erbium-doped fiber amplifiers (FM-EDFAs). The relationship of the overlap factor with the signal gain in the beat model is verified by the amplification of LP01 and LP11 modes for the first time, that is, the differential modal gain (DMG) is dependent on the integral of the overlap factor difference over the EDF length. We also simulate the effect of pump mode beating on signal amplification: the modal gain varies periodically with the pump mode phase, and the beat length can affect the fluctuation period and amplitude of the DMG. The DMG can further be reduced by controlling the initial phases of the vector modes and properly designing the beat length of the FM-EDF. The similar process can expand to more signal modes, such as the simultaneous amplification of LP01x, LP11ex, LP11oy, LP21ex and LP21oy modes. The LP mode decomposition method is also applied to the beat effect between signal modes or the amplification of orbital angular momentum (OAM) modes. One can expect to implement an experiment on the FM-EDFA amplification with pump mode beating by optimally designing the FM-EDF structure, using a properly narrow linewidth pump laser and precisely controlling the pump mode coherence.

Millimeter-Wave Wideband Dual-Polarized and Circularly Polarized ME-Dipole Reflectarrays With Linearly Polarized Feed

Millimeter-Wave Wideband Dual-Polarized and Circularly Polarized ME-Dipole Reflectarrays With Linearly Polarized Feed

Photocurrent Spectroscopy of Dark Magnetic Excitons in 2D Multiferroic NiI2.

Two-dimensional (2D) antiferromagnetic (AFM) semiconductors are promising components of opto-spintronic devices due to terahertz operation frequencies and minimal interactions with stray fields. However, the lack of net magnetization significantly limits the number of experimental techniques available to study the relationship between magnetic order and semiconducting properties. Here, they demonstrate conditions under which photocurrent spectroscopy can be employed to study many-body magnetic excitons in the 2D AFM semiconductor NiI2. The use of photocurrent spectroscopy enables the detection of optically dark magnetic excitons down to bilayer thickness, revealing a high degree of linear polarization that is coupled to the underlying helical AFM order of NiI2. In addition to probing the coupling between magnetic order and dark excitons, this work provides strong evidence for the multiferroicity of NiI2 down to bilayer thickness, thus demonstrating the utility of photocurrent spectroscopy for revealing subtle opto-spintronic phenomena in the atomically thin limit.

On the Flux Density Spectral Property of High Linearly Polarized Signal from Pulsar J0332+5434

The polarization position angles (PPA) of time samples with high linear polarization often show two parallel tracks across the pulsar profile that follow the rotating vector model (RVM). This feature supports coherent curvature radiation (CCR) as the underlying mechanism of radio emission from pulsars, where the parallel tracks of the PPA represent the orthogonal extraordinary (X) and ordinary (O) eigenmodes of strongly magnetized pair plasma. However, the frequency evolution of these high linearly polarized signals remains unexplored. In this work, we explore the flux density spectral nature of high linearly polarized signals by studying the emission from PSR J0332+5434 over a frequency range between 300 and 750 MHz, using the Giant Metrewave Radio Telescope. The pulsar average profile comprises a central core and a pair of conal components. We find the high linearly polarized time samples to be broadband in nature, and in many cases, they resemble a narrow spiky feature in the conal regions. These spiky features are localized within a narrow pulse longitude over the entire frequency range, and their spectral shapes sometimes resemble an inverted parabolic shape. In all such cases, the PPA is exclusively along one of the orthogonal RVM tracks, likely corresponding to the X-mode. The inverted spectral shape can, in principle, be explained if the high linearly polarized emission in these time samples is formed due to the incoherent addition of CCR from a large number of charged solitons (charge bunches) exciting the X-mode.

An Extremely Active Repeating Fast Radio Burst Source in a Likely Nonmagneto-ionic Environment

Fast radio bursts (FRBs) are bright radio bursts originating at cosmological distances. Only three repeating FRBs FRB 20121102A, FRB 20190520B, and FRB 20201124A among ∼60 known repeating FRBs have circular polarization. We observed the FRB 20220912A with the Robert C. Byrd Green Bank Telescope (GBT) at L-band on 2022 October 24 and detected 128 bursts in 1.4 hr, corresponding to a burst rate of about 90 hr−1, which is the highest yet for FRBs observed by the GBT. The average rotation measure (RM) was −0.4 ± 0.3 rad m−2 with negligible intraday RM change, indicating a likely nonmagneto-ionic environment. A total of 61% of bursts have a linear polarization fraction greater than 90%. Approximately 56% of the bright bursts have circular polarization. A downward drift in frequency and polarization angle swings were found in our sample. The characterization of FRB 20220912A indicates that the circular polarization is unlikely to be caused by the magneto-ionic environment for at least some of the repeating FRB population.

Ultra-wideband and high-efficiency polarization rotator based on liquid crystals

We propose a novel design of an asymmetrically anchored negative liquid crystal (LC) cell capable of linearly rotating the polarization axis of broadband light, with the rotation angle controlled by voltage. Unlike conventional LC cells that require polarization filters or retarders, our LC cell can directly modulate the polarization state of light without any additional components. The LC cell exhibits high polarization rotation efficiency over a wide wavelength range (200 nm to 2000nm), superior to the existing polarization modulators. We validate our design through theoretical calculations and numerical simulations, proving that a degree of linear polarization of over 0.95 can be achieved in the UV, visible, and NIR regions. Our design can be applied in optical communications, biological imaging, and spectroscopic technologies.

Afterglow Linear Polarization Signatures from Shallow GRB Jets: Implications for Energetic GRBs

Gamma-ray bursts (GRBs) are powered by ultrarelativistic jets. The launching sites of these jets are surrounded by dense media, which the jets must cross before they can accelerate and release high-energy emission. Interaction with the medium leads to the formation of a mildly relativistic sheath around the jet, resulting in an angular structure to the jet’s asymptotic Lorentz factor and energy per solid angle, which modifies the afterglow emission. We build a semi-analytical tool to analyze the afterglow light curve and polarization signatures of jets observed from a wide range of viewing angles, and focus on ones with slowly declining energy profiles known as shallow jets. We find overall lower polarization compared to the classical top hat jet model. We provide an analytical expression for the peak polarization degree as a function of the energy profile power-law index, magnetic field configuration, and viewing angle, and show that it occurs near the light-curve break time for all viewers. When applying our tool to GRB 221009A, suspected to originate from a shallow jet, we find that the suggested jet structures for this event agree with the upper limits placed on the afterglow polarization in the optical and X-ray bands. We also find that at early times the polarization levels may be significantly higher, allowing for a potential distinction between different jet structure models and possibly constraining the magnetization in both forward and reverse shocks at that stage.

Corrosion of Copper, Cupronickel, Nickel Aluminium Bronze and Super-Duplex Stainless Steel Rotating Cylinder Electrodes in Seawater under Turbulent Flow Conditions

The corrosion of uncoated metals in a marine environment restricts the choice of suitable engineering metals and alloys. Anodic dissolution of metal and cathodic reduction of oxygen are important processes and formation of a surface oxide film can affect both electrode reactions. Charge transfer and mass transfer data can provide information on corrosion rate and mechanism. Several metals and alloys having a history of use in marine engineering are considered, including copper, two copper alloys (cupronickel and nickel aluminium bronze) plus a more recent addition to strong, corrosion resistant alloys (a super duplex stainless steel). The rotating cylinder electrode offers the benefits of a controlled, turbulent flow of electrolyte, facilitating controlled mass transfer in a compact cell geometry which is well-suited to bench-top operation. These features are illustrated using a variety of electrochemical techniques, including open-circuit potential vs time monitoring, linear sweep voltammetry, rotation speed step- or potential step current transients and linear polarisation resistance measurements. Seawater taken from Langstone Harbour, Hampshire, UK, was filtered, air-saturated, pH 8.0 and maintained at 25 °C. Dimensionless group correlations and graphical plots (using an analogous approach to the Koutecky-Levich equation for an RDE) enabled contributions of charge transfer-, mixed- and mass transfer- controlled data to be appreciated, allowing the Tafel slopes of electrode reactions, the diffusion coefficient of dissolved oxygen, the mass transfer coefficient for oxygen reduction and the mean corrosion rate to be estimated.

Morphologies of Bright Complex Fast Radio Bursts with CHIME/FRB Voltage Data

We present the discovery of 12 apparently nonrepeating fast radio burst (FRB) sources, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources, only one of which has been presented previously in the first CHIME/FRB catalog, were selected from a database comprising O(103) CHIME/FRB full-array raw voltage data recordings, based on their large signal-to-noise ratios and complex morphologies. Our study examines the time-frequency characteristics of these bursts, including drifting, microstructure, and periodicities. The events in this sample display a variety of unique drifting phenomenologies that deviate from the linear negative drifting phenomenon seen in many repeating FRBs, and motivate a possible new framework for classifying drifting archetypes. Additionally, we detect microstructure features of duration ≲50 μs in seven events, with some as narrow as ≃7 μs. We find no evidence of significant periodicities between subburst components. Furthermore, we report the polarization characteristics of seven events, including their polarization fractions and Faraday rotation measures (RMs). The observed ∣RM∣ values span a wide range of 17.24(2)–328.06(2) rad m−2, with apparent linear polarization fractions between 0.340(1) and 0.946(3). The morphological properties of the bursts in our sample appear broadly consistent with predictions from both relativistic shock and magnetospheric models of FRB emission, as well as propagation through discrete ionized plasma structures. We address these models and discuss how they can be tested using our improved understanding of morphological archetypes.

Discovery of Perun (G329.9-0.5): A New, Young, Galactic SNR

Abstract We present the discovery of possibly the youngest Galactic supernova remnant (SNR) with associated pulsar-wind nebula (PWN), which we name Perun (G329.9-0.5). Perun was serendipitously discovered in the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey at 943 MHz, and subsequent follow up observations were conducted with the Australia Telescope Compact Array (ATCA) observatory at 5500 and 9000 MHz. We combine these with additional radio observations from the MeerKAT, Molonglo Observatory Synthesis Telescope (MOST) and MurchisonWidefield Array (MWA) telescopes, infrared (IR) observations from the Spitzer Space Telescope, and X-ray observations from the Chandra X-ray observatory to perform a multi-frequency analysis. The radio morphology shows a small angular size shell (D=70 arcsec) with a luminous, central PWN. We measure a total spectral index of α = −0.49 ± 0.05, which should be typical for a young, composite SNR. Crucial evidence for Perun’s SNR classification comes from the detection of linear fractional polarisation at radio frequencies of ∼7–10 per cent with both radial and tangential orientations, similar to the young SNR G1.9+0.3. We use data from the Southern Galactic Plane Survey (SGPS) to perform an H i analysis and estimate a favoured distance range of 6–9 kpc, and thus a favoured age range of ∼70–500 years. We find no high-energy emission in Fermi-LAT data. We detect Perun’s outer shell in 24 μm indicating the possible presence of [O iv] and [Fe iii] emission, also typical for young SNRs. Overall, these observations and analysis confirm Perun as a young, Galactic SNR with a prominent PWN.

Generation of arbitrarily patterned polarizers using 2-photon polymerization

Patterned polarizers are prepared using liquid crystals (LC) doped with a black dichroic dye and in combination with a linear polarizer. The pattern is achieved with a nanostructured LC alignment surface, that is generated using a two-photon polymerization direct laser write (2PP-DLW). This technique creates a pattern of high-resolution grooves in the photoresist at any arbitrary angle. The angle governs the LC orientation at any substrate surface point, determining the transmitted light linear polarization angle. This paper presents the first use of a 2PP-DLW cured positive tone photoresist for dichroic dye-doped LC alignment. Two complementary photoresists have been employed: conventional negative tone SU-8 photoresist and, in this context novel, positive tone S1805 photoresist. The alignment quality of the polarizers has been assessed by analyzing the transmission using an additional polarizer. For SU-8, the resulting grayscale pattern and a contrast ratio (CR) of 14 has measured. The uniformity of the alignment has been measured to be 65% using normalized Shannon entropy (H). For S1805, a CR of 37 was measured, and a uniformity of 63% was obtained. 2PP-DLW allows for shaping complex patterns in submicron dimensions and for the fabrication of arbitrarily patterned polarizers and other LC devices.

The relationship between chlorophyll fluorescence and polarized light field: Polarization-Curve Fluorescence Height

The impact of the un-polarized nature of chlorophyll fluorescence, which causes a dip in the degree of polarization of the underwater light field matching the fluorescence spectrum, led to the development of a theoretical relationship indicating that the resulting fractional reduction in observed polarization is linearly proportional to the magnitude of the fluorescence causing it. To evaluate this relationship, we used a vector radiative transfer code (VRTE) for the coupled atmosphere-ocean system using measured inherent optical properties (IOPs) for a variety of oligotrophic and eutrophic waters as inputs. The VRTE was used to simulate elastic components of the underwater reflectance as well as the degree of linear polarization (DoLP) for these different conditions. These values were compared with the underwater reflectances and the DoLPs measured by a multi-angular hyperspectral polarimeter to determine the magnitude of the fluorescence component in the reflectance spectra at 685 nm, and the decrease of the DoLP due to the fluorescence impact at the same wavelength. Fluorescence magnitudes retrieved from the differences between simulated and measured reflectances were found to match well the magnitudes estimated through the relationship based on the drop of the DoLP. It is noted that retrieval accuracies increase for both larger fluorescence and larger underlying DoLP values. Furthermore, a new method is evolved from the measured polarization analysis, Polarization-Curve Fluorescence Height (PCFH). Measured polarization were used to approximate the elastic signal and derive the inelastic un-polarized signal (fluorescence) from the difference in the fluorescence vicinity. These results open possibilities for estimating the magnitude of natural fluorescence using polarization measurements below or above the water surface, .in-situ, or remotely from aircraft or future satellites. Results of ongoing work on potential sensitivities and retrieval accuracies for these applications will be reported.

Linear polarization study of open clusters in the anticenter direction: Signature of the spiral arms

Aims. Our objective is to investigate the distribution of dust and associated large-scale structures of the Galaxy using optical linear polarization measurements of various open clusters located at different distances in the Galactic anticenter direction. Methods. We present R-band linear polarization observations of stars toward five open clusters: Kronberger 1, Berkeley 69, Berkeley 71, Berkeley 19, and King 8 in the anticenter direction. The polarization observations were carried out using the ARIES (Aryabhatta Research Institute of Observational Sciences) IMaging POLarimeter mounted on the 104 cm Sampurnanand telescope of ARIES, Nainital, making it the first study to target the polarization observations toward distant clusters (~6 kpc). We combined the observed polarization data with the distance information from the Gaia space telescope to infer the dust distribution along the line of sight. Results. The variation in the degree of polarization and extinction with distance reveals multiple dust layers in each cluster direction. In addition, common foreground-dust layers detected toward different cluster directions highlight global features such as spiral arms. Our results show that the dust clouds at 2 kpc toward Berkeley 69 and Berkeley 71 coincide with the Perseus arm, while the dust layer at ~4 kpc toward the distant clusters Berkeley 19 and King 8 indicates the presence of the Outer arm. The large-scale dust distribution obtained by combining our polarization results with previous polarization studies of nearby open clusters suggests that the anticenter direction is characterized by a low-extinction homogeneous dust distribution with a somewhat uniform orientation of the plane-of-sky component of the magnetic field along the line of sight. Conclusions. Our study demonstrates that polarization is useful as a tool for studying the large-scale dust distribution and structural features where kinematic distance methods are inadequate and cannot provide accurate distances to the dust clouds. The global dust distribution in the anticenter direction shows signatures of the intervening spiral arms.

Integrated optical probing scheme enabled by localized-interference metasurface for chip-scale atomic magnetometer

Abstract Emerging miniaturized atomic sensors such as optically pumped magnetometers (OPMs) have attracted widespread interest due to their application in high-spatial-resolution biomagnetism imaging. While optical probing systems in conventional OPMs require bulk optical devices including linear polarizers and lenses for polarization conversion and wavefront shaping, which are challenging for chip-scale integration. In this study, an integrated optical probing scheme based on localized-interference metasurface for chip-scale OPM is developed. Our monolithic metasurface allows tailorable linear polarization conversion and wavefront manipulation. Two silicon-based metasurfaces namely meta-polarizer and meta-polarizer-lens are fabricated and characterized, with maximum transmission efficiency and extinction ratio (ER) of 86.29 % and 14.2 dB for the meta-polarizer as well as focusing efficiency and ER of 72.79 % and 6.4 dB for the meta-polarizer-lens, respectively. A miniaturized vapor cell with 4 × 4 × 4 mm3 dimension containing 87Rb and N2 is combined with the meta-polarizer to construct a compact zero-field resonance OPM for proof of concept. The sensitivity of this sensor reaches approximately 9 fT/Hz1/2 with a dynamic range near zero magnetic field of about ±2.3 nT. This study provides a promising solution for chip-scale optical probing, which holds potential for the development of chip-integrated OPMs as well as other advanced atomic devices where the integration of optical probing system is expected.

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

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

Survey of non-thermal electrons around supermassive black holes through polarization flips

Abstract Optically thick non-thermal synchrotron sources notably produce linear polarization vectors that are parallel to projected magnetic field lines on the observer’s screen, although they are perpendicular in well-known optically thin cases. To elucidate the complex relationship between the vectors and fields, and to investigate the energy and spatial distribution of non-thermal electrons through the images, we perform polarization radiative transfer calculations at submillimeter wavelengths. Here the calculations are based on semi-analytic force-free jet models with non-thermal electrons with a power-law energy distribution. In the calculated images, we find a $90{^\circ }$-flip of linear polarization vectors at the base of counter-side (receding) jet near a black hole, which occurs because of large optical depths for the synchrotron self-absorption effect. The $90{^\circ }$-flip of LP vectors is also seen on the photon ring at a high frequency, since the optical depth along the rays is large there due to the light bending effect. In addition, we see the flip of the sign of circular polarization components on the counter-jet and photon ring. Furthermore, we show that these polarization flips are synthesized with large values in the spectral index map, and also give rise to outstanding features in the Faraday Rotation Measure map. Since the conditions of flipping depend on the magnetic field strength and configuration and the energy distribution of electrons, we can expect that the polarization flips will provide us with observational evidence for the presence of non-thermal electrons around the black hole, and a clue to the magnetic driving mechanism of plasma jets.

Investigation on electrochemical corrosion behavior of Cu-14Fe -(0, 0.05)Ce alloys

This work thoroughly investigated the electrochemical corrosion behaviors of Cu-14Fe-(0, 0.05) Ce alloys. Experimental findings revealed that the addition of Ce did not change the phase constituent, but refined α-Fe phase particle from 0.30 ± 0.04 to 0.22 ± 0.03 μm and increased its content from 1.24% to 2.17%. With the increase of corrosion time, adding Ce could increase the linear polarization resistance by up to 3 times, and correspondingly the corrosion rate was reduced to half. Moreover, Ce addition contributed to the densification of corrosion products. The α-Fe phase preferentially underwent anodic dissolution reaction, generating corrosion product Fe2O3. The increase of soaking time resulted in the occurrence of anodic dissolution of Cu-matrix phase, along with the formation of Cu2O and Cu2Cl(OH)3.

Evaluation of Corrosion Performance of LDX 2101 and UNS S32205 in Flexible Pipeline Applications: A Comparative Study

Lean duplex stainless steel (LDSS) has been used in various applications, including flexible pipelines in offshore and other industrial settings. In recent years, LDSS has become the preferred choice over standard duplex stainless steel (DSS) for flexible pipeline applications due to its lower costs, achieved by reducing nickel and molybdenum content, while still providing comparable corrosion resistance and mechanical strength properties to DSS. However, there is still limited reporting on the corrosion effects of reducing these alloys on the behaviour of lean duplex stainless steel in flexible pipelines. This comparative study investigates the corrosion resistance of lean duplex stainless steel, LDX 2101 and duplex stainless steel, UNS S32205 in flexible pipeline applications using linear polarization resistance (LPR). The research focuses on assessing material performance in environments containing CO2 and H2S, commonly found in oil and gas production, by conducting short-term and long-term tests to evaluate pitting and selective corrosion. The samples, LDX 2101 and UNS S32205 were immersed in a 3.5M NaCl solution, and corrosion measurements were performed using the Metrohm Autolab potentiostat. The results indicate that both materials exhibit good corrosion resistance, but there are differences in their performance under specific conditions. While lean duplex stainless steel, LDX 2101, can be used as a substitute for duplex stainless steel UNS S32205, its corrosion resistance and mechanical properties gradually decrease over time due to the reduced nickel and molybdenum content. As a result, it would not be as effective as duplex stainless steel UNS S32205 in withstanding corrosion in aggressive conditions over a prolonged period.