Faraday Rotation Research Articles

Faraday rotation stimulated optical-rotation quasi-phase-matching technique to radiate a highly efficient elliptically polarized second harmonic

Faraday rotation has been employed to ensure efficient frequency conversion in the ultraviolet regime. The reported 36% efficiency of the radiated 372 nm, continuous-wave second harmonic of this paper has been numerically analyzed in the presence of a magnetic field in a thin-film-coated magneto-optic crystal using the total-internal-reflection-based optical-rotation quasi-phase-matching approach, considering the influence of surface roughness, absorption loss, and the nonlinear law of reflection.

Quantum refraction effects in pulsar emission

ABSTRACT Highly magnetized neutron stars exhibit the vacuum non-linear electrodynamics effects, which can be well-described using the one-loop effective action for quantum electrodynamics. In this context, we study the propagation and polarization of pulsar radiation, based on the post-Maxwellian Lagrangian from the Heisenberg–Euler–Schwinger action. Given the refractive index obtained from this Lagrangian, we determine the leading-order corrections to both the propagation and polarization vectors due to quantum refraction via perturbation analysis. In addition, the effects on the orthogonality between the propagation and polarization vectors and the Faraday rotation angle, all due to quantum refraction are investigated. Furthermore, from the dual refractive index and the associated polarization modes, we discuss quantum birefringence, with the optical phenomenology analogous to its classical counterpart.

Real-time deep-learning-based object detection and unsupervised statistical analysis for quantitative evaluation of defect length direction on magnetooptical faraday effect

Magnetooptical nondestructive inspection (MONDI) is widely used in various industries to detect defects in metal including ferromagnetic materials. Despite its high precision and sensitivity, its inspection accuracy is highly dependent on the direction of the magnetizer. In addition, the irregular shapes of defects make the assessment of their severity challenging. To address these limitations, we propose an efficient real-time deep learning (DL)-based object detection model called the MONDI detector. This model is designed to integrate a DL-based object detection model with statistical analysis based on regression model to classify and quantify the magnetizer direction. To comprehensively assess algorithm performance, this study investigates variations in the excitation field, defect shape, and defect depth. This analysis is expected to contribute to the state-of-the-art object detection paradigm in MONDI system.

Exact closed forms for the transmittance of electromagnetic waves in one-dimensional anisotropic periodic media

In this work, we obtain closed expressions for the transfer matrix and the transmittance of electromagnetic waves propagating in finite one-dimensional anisotropic periodic stratified media with an arbitrary number of cells. By invoking the Cayley–Hamilton theorem on the transfer matrix for the electromagnetic field in a periodic stratified media formed by N cells, we obtain a fourth-order recursive relation for the matrix coefficients that defines the so-called Tetranacci polynomials (TPs). In the symmetric case, corresponding to a unit-cell transfer matrix with a characteristic polynomial where the coefficients of the linear and cubic terms are equal, closed expressions for the solutions to the recursive relation, known as symmetric TPs, have recently been derived, allowing us to write the transfer matrix and transmittance in a closed form. We show as sufficient conditions that the 4×4 differential propagation matrix of each layer in the binary unit cell, Δ , a) has eigenvalues of the form ±p1 , ±p2 , with p1≠p2 , and b) its off-diagonal 2×2 block matrices possess the same symmetric structure in both layers. Otherwise, the recursive relations are still solvable for any 4×4 matrix and provide an algorithm to compute the Nth power of the transfer matrix without carrying out explicitly the matrix multiplication of N matrices. We obtain analytical expressions for the dispersion relation and transmittance, in closed form, for two finite periodic systems: the first one consists of two birefringent uniaxial media with their optical axis perpendicular to the z-axis, and the second consists of two isotropic media subject to an external magnetic field oriented along the z-axis and exhibiting the Faraday effect. Our formalism applies also to lossy media, magnetic anisotropy or optical activity.

A Millisecond Pulsar Binary Embedded in a Galactic Center Radio Filament

The Galactic center is host to a population of extraordinary radio filaments, thin linear structures that trace out magnetic field lines running perpendicular to the Galactic plane. Using Murriyang, the 64 m Parkes radio telescope, we conducted a search for pulsars centered on the position of a compact source in the filament G359.0−0.2. We discovered a millisecond pulsar (MSP), PSR J1744−2946, with a period P = 8.4 ms, that is bound in a 4.8 hr circular orbit around an M c > 0.05 M ⊙ companion. The pulsar dispersion measure of 673.7 ± 0.1 pc cm−3 and Faraday rotation measure of 3011 ± 3 rad m−2 are the largest of any known MSP. Its radio pulses are moderately scattered due to multipath propagation through the interstellar medium, with a scattering timescale of 0.87 ± 0.08 ms at 2.6 GHz. Using MeerKAT, we localized the pulsar to a point source embedded in a low-luminosity radio filament, the “Sunfish”, that is unrelated to G359.0−0.2. Our discovery of the first MSP within 1° of the Galactic center hints at a large population of these objects detectable via high-frequency surveys. The association with a filament points to pulsars as the energy source responsible for illuminating the Galactic center radio filaments.

The Huge Magnetic Toroids in the Milky Way Halo

The magnetic fields in our Milky Way can be revealed by the distribution of Faraday rotation measures (RMs) of radio sources behind the Galaxy and of radio pulsars inside the Galaxy. Based on the antisymmetry of the Faraday sky in the inner Galaxy to the Galactic coordinates, the magnetic field toroids above and below the Galactic plane with reversed field directions exist in the Galactic halo and have been included in almost all models for the global magnetic structure in the Milky Way. However, the quantitative parameters—such as the field strength, the scale height, and the scale radius of the toroids—are hard to determine from observational data. It has long been argued that the RM antisymmetry could be dominated by the local contributions of the interstellar medium. Here, we get the local-discounted RM contributions from the RM sky and RMs of pulsars and get the first quantitative estimate of the sizes of the magnetic toroids in the Galactic halo. They are huge, starting from a Galactocentric radius of less than 2 kpc and extending to at least 15 kpc, without field direction reversals. Such magnetic toroids in the Galactic halo should naturally constrain the physical processes in galaxies.

Circular dichroism in nonlinear topological Weyl semimetals

In recent years, the field of topological photonics has emerged as a promising area of research due to its potential for the development of new photonic devices with unique properties. Topological Weyl semimetals (TWSs), which are characterized by the presence of Weyl points in their electronic band structure, are one such example of a material with interesting topological properties. In this study, Kerr and Faraday rotations were used to determine the nonlinear characteristics of TWSs. We focused on surfaces where no Fermi arcs are involved, so that Maxwell’s equations would contain some peculiar topological terms. In Weyl semimetals with a specific topology, the distance between Weyl nodes aligned along the z-direction functions as a magnet. This results in a significant polar Kerr/Faraday rotation effect that is proportional to the separation distance, when light is directed onto the surface of the TWS that lacks Fermi arc states. Conversely, when the light is directed onto a surface with Fermi arc states, the Voigt effect is quadratically proportional to the separation distance. We considered electromagnetic wave propagation in a nonlinear Kerr-type medium. We have derived and solved the linear and nonlinear Helmholtz equations for TWSs using the tanh method. Our findings reveal that wave solutions could have some potentially significant implications for the design and optimization of photonic devices based on TWSs.

Estimation of ionospheric Faraday rotation over ocean areas using L-band spaceborne PolSAR data

ABSTRACT L-band spaceborne polarimetric synthetic aperture radar (PolSAR) data has been well used for the high-resolution retrieval of the ionospheric Faraday rotation (FR). A vast majority of these retrievals were, however, conducted on PolSAR data of lands, with only a very few over oceans. For the global imaging of the Earth’s ionosphere, the retrieval of oceanic ionosphere is indispensable. This paper aims to furnish a deep insight into the FR retrieval on oceans using the widely used Bickel-Bates estimator based on the two cross-circular polarizations Z 12 and Z 21 . The FR estimates (FRE) on oceans are evaluated in detail by comparing with those on lands on four ALOS PALSAR datasets. The achieved oceanic FRE are shown to possess comparable or even better quality than those on lands. It occurs in three of the four scenes that the selected ocean sub-area holds a smaller standard deviation (STD) of FRE (less than 0.7000°) than all the selected land sub-areas. Especially, the quality of FRE is shown to be closely linked to the dispersed degree of the magnitude of the conjugate product of Z 12 and Z 21 via the analysis of coefficient of variation (CV), according to which the unusual occurrence of larger magnitude level corresponding to larger STD of FRE can be explained. Nevertheless, compared with CV, the magnitude of the polarimetric coherence between Z 12 and Z 21 (i.e. γ ) is identified as a better index to measure the quality of FRE. A smaller STD of FRE appears along with a larger γ . Three of the four scenes show that the selected ocean sub-area bears a larger mean of γ (greater than 0.9890) in comparison with all the selected land sub-areas. This work can promote the ionospheric research over oceans and to the correction of ionospheric effects in oceanic L-band spaceborne polarimetric radar data as well.

Measuring non-linear Faraday rotation in cold atoms in presence of persistent transverse fields using tunable differential imaging

Non-linear Faraday rotation in cold atoms promises precision magnetometry due to narrower magnetic resonance linewidth compared to the linear Faraday effect. Imaging techniques based on linear Faraday effect have emerged as a tool to characterize the dynamics of ultracold atomic clouds. Using a camera instead of balanced detectors, we can obtain the spatial distribution of polarization rotation in a uniformly intense optical beam. However, the finite dynamic range of the imaging device limits the sensitivity to measure non-linear Faraday rotation at a given incident power. Here, we experimentally demonstrate a differential imaging technique in which we can tune parameters to improve contrast and the sensitivity to the non-linear Faraday rotation signal by a factor of ≈7 over existing imaging methods. The atomic cloud experiences a uniform optical field even when shifted by persistent magnetic fields making the method robust. This allows us to study the effect of transverse fields on non-linear Faraday rotation in ultra-cold atoms, paving the way toward spatially resolved vector magnetometry.

Giant reduced magnetic anisotropy in magneto-optical garnet

Magneto-optical garnet shows great potential in integrated optical isolators due to its highly efficient non-reciprocity. In this work, we prepared magneto-optical lithium-modified terbium bismuth iron garnet films using the liquid phase epitaxy method and systemically investigated the effect of lithium modification on magnetic properties. We found a trace amount of lithium modification induced in-plane magnetization and a minimum in-plane driving field around 2 Oe. Meanwhile, high remanence over 70% was obtained in tensile-strain samples. Most importantly, in comparison to unmodified samples, the calculation of anisotropy demonstrated the giant reduction of growth-induced anisotropy in the Li: TbBiIG up to 105erg/cm3. It reveals a new rule of ions’ preferred occupation in dodecahedral sublattices indirectly. Furthermore, enhanced Faraday rotation in the near-infrared band was confirmed in the samples about 1 micrometer, up to 48% higher than unmodified samples. Our work shows Li:TbBiIGs enable a prime candidate material with substantial potential for integrated optical isolation applications.

Gravitational Faraday rotation of light propagation in the Kerr–Newman–Taub–NUT space-time

Gravitational Faraday rotation of light propagation in the Kerr–Newman–Taub–NUT space-time

Weak Faraday Effect Measurement in Anti-Resonant Fiber Based on Intermodal Interference Suppression

Anti-resonant fiber (ARF) works well in a relatively strong magnetic field due to its weak Faraday effect, which results from the fundamental mode mainly transmitting in the air core. Accurately measuring the Faraday effect strength, i.e., the effective Verdet constant, of an ARF determines its applicable scenarios. However, the effective Verdet constant of ARF is ~3 orders of magnitude lower than that of a standard single-mode fiber, which is very difficult to measure. In this paper, we reveal that intermodal interference is the main obstacle to measuring the ultralow effective Verdet constant of ARF and propose using a narrow-band low-coherence light to suppress it. The measured effective Verdet constant of ARF is 0.423 ± 0.005 mrad/T/m at 1550 nm.

Giant Faraday rotation in atomically thin semiconductors

Faraday rotation is a fundamental effect in the magneto-optical response of solids, liquids and gases. Materials with a large Verdet constant find applications in optical modulators, sensors and non-reciprocal devices, such as optical isolators. Here, we demonstrate that the plane of polarization of light exhibits a giant Faraday rotation of several degrees around the A exciton transition in hBN-encapsulated monolayers of WSe2 and MoSe2 under moderate magnetic fields. This results in the highest known Verdet constant of -1.9 × 107 deg T−1 cm−1 for any material in the visible regime. Additionally, interlayer excitons in hBN-encapsulated bilayer MoS2 exhibit a large Verdet constant (VIL ≈ +2 × 105 deg T−1 cm−2) of opposite sign compared to A excitons in monolayers. The giant Faraday rotation is due to the giant oscillator strength and high g-factor of the excitons in atomically thin semiconducting transition metal dichalcogenides. We deduce the complete in-plane complex dielectric tensor of hBN-encapsulated WSe2 and MoSe2 monolayers, which is vital for the prediction of Kerr, Faraday and magneto-circular dichroism spectra of 2D heterostructures. Our results pose a crucial advance in the potential usage of two-dimensional materials in ultrathin optical polarization devices.

Laboratory evidence of Weibel magnetogenesis driven by temperature gradient using three-dimensional synchronous proton radiography.

The origin of the cosmic magnetic field remains an unsolved mystery, relying not only on specific dynamo processes but also on the seed field to be amplified. Recently, the diffuse radio emission and Faraday rotation observations reveal that there has been a microgauss-level magnetic field in intracluster medium in the early universe, which places strong constraints on the strength of the initial field and implies the underlying kinetic effects; the commonly believed Biermann battery can only provide extremely weak seed of 10-21 G. Here, we present evidence for the spontaneous Weibel-type magnetogenesis in laser-produced weakly collisional plasma with the three-dimensional synchronous proton radiography, where the distribution anisotropy directly arises from the temperature gradient, even without the commonly considered interpenetrating plasmas or shear flows. This field can achieve sufficient strength and is sensitive to Coulomb collision. Our results demonstrate the importance of kinetics in magnetogenesis in weakly collisional astrophysical scenarios.

Space Domain Awareness Observations Using the Buckland Park VHF Radar

There is increasing interest in space domain awareness worldwide, motivating investigation of the use of non-traditional sensors for space surveillance. One such class of sensor is VHF wind profiling radars, which have a low cost relative to other radars typically applied to this task. These radars are ubiquitous throughout the world and may potentially offer complementary space surveillance capabilities to the Space Surveillance Network. This paper updates an initial investigation on the use of Buckland Park VHF wind profiling radars for observing resident space objects in low Earth orbit to further investigate the space surveillance capabilities of the sensor class. The radar was operated during the Australian Defence “SpaceFest” 2019 activity, incorporating new beam scheduling and signal processing functionality that extend upon the capabilities described in the initial investigation. The beam scheduling capability used two-line element propagations to determine the appropriate beam direction to use to observe transiting satellites. The signal processing capabilities used a technique based on the Keystone transform to correct for range migration, allowing the development of new signal processing modes that allow the coherent integration time to be increased to improve the SNR of the observed targets, thereby increasing the detection rate. The results reveal that 5874 objects were detected over 10 days, with 2202 unique objects detected, representing a three-fold increase in detection rate over previous single-beam direction observations. The maximum detection height was 2975.4 km, indicating a capability to detect objects in medium Earth orbit. A minimum detectable RCS at 1000 km of −10.97 dBm2 (0.09 m2) was observed. The effects of Faraday rotation resulting from the use of linearly polarised antennae are demonstrated. The radar’s utility for providing total electron content (TEC) measurements is investigated using a high-range resolution mode and high-precision ephemeris data. The short-term Fourier transform is applied to demonstrate the radar’s ability to investigate satellite rotation characteristics and monitor ionospheric plasma waves and instabilities.

Direct observation of the transition from spin waves to the magnon Bose condensate

Bose-Einstein condensation occurs at an appropriate density of bosonic particles, depending on their mass and temperature. The transition from the semiclassical paradigm of spin waves to the magnon Bose-Einstein condensed state (mBEC) was obtained experimentally with increasing magnon density. We used the Faraday rotation effect to study the spatial distribution of the magnon density and phase far from their excitation region. A coherent magnetization precession was observed throughout the sample, which indicates the formation of a magnon BEC. It is shown that this result under experimental conditions goes beyond the applicability of the Landau-Lifshitz-Gilbert semiclassical theory.

First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring

In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24%–28%, peaking at ∼40%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to ≈46° ± 12° rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow.

Deep Synoptic Array Science: Polarimetry of 25 New Fast Radio Bursts Provides Insights into Their Origins

We report on a full-polarization analysis of the first 25 as yet nonrepeating fast radio bursts (FRBs) detected at 1.4 GHz by the 110-antenna Deep Synoptic Array (DSA-110) during commissioning observations. We present details of the data-reduction, calibration, and analysis procedures developed for this novel instrument. Faraday rotation measures (RMs) are searched between ±106 rad m−2 and detected for 20 FRBs, with magnitudes ranging from 4 to 4670 rad m−2. Fifteen out of 25 FRBs are consistent with 100% polarization, 10 of which have high (≥70%) linear-polarization fractions and two of which have high (≥30%) circular-polarization fractions. Our results disfavor multipath RM scattering as a dominant depolarization mechanism. Polarization-state and possible RM variations are observed in the four FRBs with multiple subcomponents. We combine the DSA-110 sample with polarimetry of previously published FRBs, and compare the polarization properties of FRB subpopulations and FRBs with Galactic pulsars. Although FRB polarization fractions are typically higher than those of Galactic pulsars, and cover a wider range than those of pulsar single pulses, they resemble those of the youngest (characteristic ages <105 yr) pulsars. Our results support a scenario wherein FRB emission is intrinsically highly linearly polarized, and propagation effects can result in conversion to circular polarization and depolarization. Young pulsar emission and magnetospheric propagation geometries may form a useful analogy for the origin of FRB polarization.

Метод эффективных вычитаний: работа с данными Иркутского радара некогерентного рассеяния

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.

Effective subtraction technique: implementation for Irkutsk Incoherent Scatter Radar

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.