Faraday Rotation Research Articles

Magneto-optic fiber-coupled tuneable optical attenuation.

Tuneable, variable, optical attenuation through an optical circulator with a broad, linear attenuation range of Δα ∼ (30-40) dB is demonstrated using non-reciprocal Faraday rotation in a double-pass configuration with a combination of permanent magnets and an electromagnet. A fiber-coupled magneto-optical variable optical attenuator (MVOA) operates over the near IR with an attenuation tuning range of Δα > 30 dB, a resolution of Δα ∼ 0.02 dB, a response time of t < 2 ms, and a temperature dependence over T = 25-70°C of Δα / ΔT = -8 × 10-4 dB/°C. At λ = 1550 nm, the calculated Faraday material effective Verdet constant is (1/A)V eff = 109 × 103 dB/(T.m).

Generating 1.2 GHz, 38 fs stretched-pulse directly from a robust mode locked solid-state fiber laser.

We demonstrated what is believed to be the first 1.2 GHz nonlinear polarization rotation stretched-pulse mode-locked Yb:fiber laser with a compact design and innovative components. With a compact Faraday rotation angle has been used in NPR mode-locked lasers, and we find that incomplete isolation of backward-propagating light does not hinder self-starting. This laser directly outputs sub-40 fs pulses with a spectral bandwidth exceeding 70 nm, achieving over 1 W of average output power. The laser serves as a seed source, generating a supercontinuum over one octave-spanning range without external amplification or compression.

Interpolation Techniques for Reconstructing Galactic Faraday Rotation

The line-of-sight structure of the Galactic magnetic field (GMF) can be studied using Faraday rotation measure (RM) grids. We analyze how the choice of interpolation kernel can affect the accuracy and reliability of reconstructed RM maps. We test the following kernels: inverse distance weighting (IDW), natural neighbor interpolation (NNI), inverse multiquadric interpolation (IM), thin-plate spline interpolation (TPS), and a Bayesian rotation measure sky (BRMS); all techniques were tested on two simulated Galactic foreground RMs (one assuming the GMF has patchy structures and the other assuming it has filamentary structures) using magnetohydrodynamic simulations. Both foregrounds were sampled to form RM grids with densities of ∼40 sources deg−2 and area ∼144 deg2. The techniques were tested on data sets with different noise levels and Gaussian random extragalactic RM contributions. The data set that most closely emulates expected data from current surveys, such as the POlarization Sky Survey of the Universe’s Magnetism (POSSUM), had extragalactic contributions and a noise standard deviation of ∼1.5 rad m−2. For this data set, the accuracy of the techniques for the patchy structures is ranked from best to worst as BRMS, NNI, TPS, IDW, and IM; in the filamentary simulated foreground, the ordering is BRMS, NNI, TPS, and IDW. IDW is the most computationally expensive technique, while TPS and IM are the least expensive. BRMS and NNI have the same, intermediate computational cost. This analysis lays the groundwork for Galactic RM studies with large radio polarization sky surveys, such as POSSUM.

Semi-supervised rotation measure deconvolution and its application to MeerKAT observations of galaxy clusters

Context. Faraday rotation contains information about the magnetic field structure along the line of sight and is an important instrument in the study of cosmic magnetism. Traditional Faraday spectrum deconvolution methods such as RMCLEAN face challenges in resolving complex Faraday dispersion functions and handling large datasets. Aims. We developed a deep learning deconvolution model to enhance the accuracy and efficiency of extracting Faraday rotation measures from radio astronomical data, specifically targeting data from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). Methods. We used semi-supervised learning, where the model simultaneously recreates the data and minimizes the difference between the output and the true signal of synthetic data. Performance comparisons with RMCLEAN were conducted on simulated as well as real data for the galaxy cluster Abell 3376. Results. Our semi-supervised model is able to recover the Faraday dispersion for extended rotation measure (RM) components, while accounting for bandwidth depolarization, resulting in a higher sensitivity for high-RM signals, given the spectral configuration of MGCLS. Applied to observations of Abell 3376, we find detailed magnetic field structures in the radio relics, and several active galactic nuclei. We also applied our model to MeerKAT data of Abell 85, Abell 168, Abell 194, Abell 3186, and Abell 3667. Conclusions. We have demonstrated the potential of deep learning for improving RM synthesis deconvolution, providing accurate reconstructions at a high computational efficiency. In addition to validating our data against existing polarization maps, we find new and refined features in diffuse sources imaged with MeerKAT.

Making the Invisible Visible: Magnetic Fields in Accretion Flows Revealed by X-Ray Polarization

Large-scale, strong magnetic fields are often evoked in black hole accretion flows, for jet launching in the low/hard state and to circumvent the thermal instability in the high/soft state. Here, we show how these ideas are strongly challenged by X-ray polarization measurements from the Imaging X-ray Polarimetry Explorer (IXPE). Quite general arguments show that equipartition large-scale fields in the accretion flow should be of order 106–8 G. These produce substantial Faraday rotation and/or depolarization. Since IXPE observes polarization in both spectral states, this sets upper limits to coherent large-scale (vertical, radial, or azimuthal) magnetic fields in the photosphere of B ≲ 5 × 106 G. While we stress that Faraday rotation should be calculated for each individual simulation (density, field geometry, and emissivity), it seems most likely that there are no equipartition-strength large-scale ordered fields inside the photosphere of the X-ray-emitting gas. Strong poloidal fields can still power a Blandford–Znajek jet in the low/hard state if they thread the black hole horizon rather than the X-ray-emitting flow, but this could also be challenged by (lack of) depolarization from vacuum birefringence. Instead, an alternative solution is that the low/hard state jet is dominated by pairs, so can be accelerated by lower fields. Strong toroidal fields could still stabilize the disk in the high/soft state if they are buried beneath the photosphere, though this seems unlikely due to magnetic buoyancy. Fundamentally, polarization data from IXPE mean that magnetic fields in black hole accretion flows are no longer invisible and unconstrained.

Improved Computerized Ionospheric Tomography Based on GPS and PALSAR Data

AbstractDue to factors such as the uneven distribution of ground receiving stations and the lack of effective observation rays, Global Positioning System (GPS)‐based computerized ionospheric tomography (CIT) is typically of low quality and requires additional data sources. Recently, Faraday rotation angle (FRA) retrieval using the Phased Array L‐band Synthetic Aperture Radar (PALSAR) full‐pol data have emerged as a reliable technique for ionospheric detection. Similar to the total electron content (TEC), the FRA is the integral effect of the electron density and geomagnetic field, with the geomagnetic field being accurately estimated by the International Geomagnetic Reference Field (IGRF) model. Therefore, this paper proposes a 3‐D secondary CIT algorithm by integrating PALSAR and GPS data: first, the product of the electron density values obtained from GPS‐based CIT and the magnitude of geomagnetic field in corresponding voxel obtained from IGRF is used as the initial value. Then, the iterative algorithm is improved by using the FRA obtained from PALSAR data, rather than TEC, as the input for the second iteration, avoiding the approximation error caused by converting FRA into TEC. The geomagnetic field information is then separated by using the IGRF model, and the reconstructed spatial distribution is finally obtained. Experimental verification shows that the FRA can compensate for the lack of GPS observation rays to a certain extent and improve the accuracy of the reconstructed electron density. The results also indicate that the PALSAR can provide an effective and feasible data source for CIT.

Intergalactic Medium Rotation Measure of Primordial Magnetic Fields

The Faraday rotation effect, quantified by the rotation measure (RM), is a powerful probe of the large-scale magnetization of the Universe—tracing magnetic fields not only on galaxy and galaxy cluster scales but also in the intergalactic medium (IGM; referred to as RMIGM). The redshift dependence of the latter has extensively been explored with observations. It has also been shown that this relation can help to distinguish between different large-scale magnetization scenarios. We study the evolution of this RMIGM for different primordial magnetogenesis scenarios to search for the imprints of primordial magnetic fields (PMFs; magnetic fields originating in the early Universe) on the redshift-dependence of RMIGM. We use cosmological magnetohydrodynamic simulations for evolving PMFs during large-scale structure formation, coupled with the light-cone analysis to produce a realistic statistical sample of mock RMIGM images. We study the predicted behavior for the cosmic evolution of RMIGM for different correlation lengths of PMFs, and provide fitting functions for their dependence on redshifts. We compare these mock RM trends with the recent analysis of the the LOw-Frequency ARray RM Grid and find that large-scale-correlated PMFs should have (comoving) strengths ≲0.75 nG, if they originated during inflation with the scale-invariant spectrum and (comoving) correlation length of ∼19 h −1 cMpc or ≲30 nG if they originated during phase-transition epochs with the comoving correlation length of ∼1 h −1 cMpc. Our findings agree with previous observations and confirm the results of semi-analytical studies, showing that upper limits on the PMF strength decrease as their coherence scales increase.

Faraday Rotation Angle Measurement Based on Coupled Optoelectronic Oscillator with Temperature Compensation

Faraday Rotation Angle Measurement Based on Coupled Optoelectronic Oscillator with Temperature Compensation

A Repeating Fast Radio Burst Source in a Low-luminosity Dwarf Galaxy

We present the localization and host galaxy of FRB 20190208A, a repeating source of fast radio bursts (FRBs) discovered using CHIME/FRB. As part of the Pinpointing REpeating ChIme Sources with EVN dishes repeater localization program on the European VLBI Network (EVN), we monitored FRB 20190208A for 65.6 hr at ∼1.4 GHz and detected a single burst, which led to its very long baseline interferometry localization with 260 mas uncertainty (2σ). Follow-up optical observations with the MMT Observatory (i ≳ 25.7 mag (AB)) found no visible host at the FRB position. Subsequent deeper observations with the Gran Telescopio Canarias, however, revealed an extremely faint galaxy (r = 27.32 ± 0.16 mag), very likely (99.95%) associated with FRB 20190208A. Given the dispersion measure of the FRB (∼580 pc cm−3), even the most conservative redshift estimate ( zmax∼0.83 ) implies that this is the lowest-luminosity FRB host to date (≲108 L ⊙), even less luminous than the dwarf host of FRB 20121102A. We investigate how localization precision and the depth of optical imaging affect host association and discuss the implications of such a low-luminosity dwarf galaxy. Unlike the other repeaters with low-luminosity hosts, FRB 20190208A has a modest Faraday rotation measure of a few tens of rad m−2, and EVN plus Very Large Array observations reveal no associated compact persistent radio source. We also monitored FRB 20190208A for 40.4 hr over 2 yr as part of the Extragalactic Coherent Light from Astrophysical Transients repeating FRB monitoring campaign on the Nançay Radio Telescope and detected one burst. Our results demonstrate that, in some cases, the robust association of an FRB with a host galaxy will require both high localization precision and deep optical follow-up.

Polycrystalline magneto-optical transparent Pr2Zr2O7 pyrochlore ceramic for Faraday rotation.

To design an innovative magneto-optical material aimed at a large Verdet constant coincides with the development trend of state-of-the-art modern optical devices. In this work, a magneto-optical transparent Pr2Zr2O7 ceramic with pyrochlore structure was successfully fabricated by vacuum sintering plus hydrogen reduction for the first time to our knowledge. The two- and three-dimensional images observed on the laser scanning confocal microscopy reveal that the grain-boundary dent depth of the polished Pr2Zr2O7 ceramic is only ∼1.6 µm upon thermal etching at a high temperature of 1675°C for 2 h, showing excellent heat-resistance ability. The crystal-clear Pr2Zr2O7 ceramic has a high in-line transmittance of ∼71.6% at 780 nm (∼92.3% of the theoretical value), a high refractive index of ∼2.1, and an effective magnetic moment of ∼5.28 µ B. In the visible region, the O2- polarizability and optical basicity of the Pr2Zr2O7 compound generally retain constants around 2.37 ± 0.07 Å3 and 0.965 ± 0.015, respectively. The magneto-optical transparent Pr2Zr2O7 ceramic exhibits high Verdet constants of -336 ± 4, -208 ± 3, -108 ± 1, and -48 ± 2 rad·T-1·m-1 at 515, 635, 780, and 1064 nm, respectively, which were ∼1.55-fold higher than the commercial Tb3Ga5O12 single crystal. Our developed new-type ceramic material has excellent potential application for Faraday rotation.

Coenhancement of optical transmission and Faraday effect with magnetic plasmonic nanopillars

Coenhancement of optical transmission and Faraday effect with magnetic plasmonic nanopillars

Kilogauss magnetic field and jet dynamics in the quasar NRAO 530

The advancement of the Event Horizon Telescope has enabled the study of relativistic jets in active galactic nuclei down to sub-parsec linear scales even at high redshift. Quasi-simultaneous multifrequency observations provide insights into the physical conditions in compact regions and allow accretion theories to be tested. Initially, we aimed to measure the magnetic field strength close to the central supermassive black hole in by studying the frequency-dependent opacity of the jet matter, Faraday rotation, and the spectral index in the millimeter-radio bands. was observed quasi-simultaneously at 15, 22, 43, 86, and 227\,GHz at four different very long baseline interferometer (VLBI) networks. By means of imaging and model-fitting, we aligned the images, taken at different frequencies. We explored opacity along the jet and the distribution of the linearly polarized emission in it. Our findings reveal that the jet of at 86 and 227\,GHz is transparent down to its origin, with 70\,mJy emission detected at 227\,GHz potentially originating from the accretion disk. The magnetic field strength near the black hole, estimated at $5r_ g $, is $3 (depending on the central black hole mass). These values represent some of the highest magnetic field strengths reported for active galaxies. We also report the first ever VLBI measurement of the Faraday rotation at 43--227\,GHz, which reveals rotation measure values as high as -48000 rad/m2, consistent with higher particle density and stronger magnetic fields at the jet's outset. The complex shape of the jet in is in line with the expected behavior of a precessing jet, with a period estimated to be around $6 years.

Magnetooptical gyrotropic effects in nanosized BiYIG films and diamagnetic YAG substrates

Magneto-optical gyrotropic Faraday and Kerr effects are studied in the BiY2Fe5O12 films with thicknesses ranging from 16 to 55 nm, in the wavelength range of 295 nm &amp;lt; λ &amp;lt; 830 nm (4.2–1.5 eV), and under magnetic fields of up to 1.2 T. It is shown that films produced by ac magnetron sputtering on the single-crystalline diamagnetic yttrium aluminum garnet substrates Y3Al5O12 (001) exhibit high structural and magneto-optical quality. The Verdet constant for diamagnetic Y3Al5O12 is determined, and the magnitude of the Kerr effect is estimated for the polished substrate. It is shown experimentally that for a substrate with diffusely reflective backside, the Kerr effect is about zero, except in the high-energy region. For all BiY2Fe5O12 films investigated, in the saturating magnetic fields of approximately 0.16–0.2 T, the value of specific Faraday rotation reaches 20 deg/μm (200 000 deg/cm), while the value of the Kerr effect reaches approximately 20 min (5.8 mrad). The critical thickness of the film–substrate interface was estimated, highlighting variations in the Kerr effect spectra associated with a decrease in the Bi content in thin films with the thicknesses of below 27 nm.

Going deeper on magneto-optical Faraday effect analysis to detect fatigue crack with high-spatial resolution for non-destructive inspection

In this study, we introduce a high-resolution technique for defect detection that uses the magneto–optical (MO) Faraday effect. Our system combines a portable polarized microscope and an MO sensor for the high spatial observation of a magnetic domain structure. We accurately localized and characterized the fatigue defects through integrated image pre-processing and cross-power spectral density analysis. This approach enhances our analysis of the magnetic domain structure, increasing the spatial capabilities of the microscope to detect fatigue defects. We conducted experiments on fatigue cracks with defect depth angles of 0°, 30°, and 60°, analyzing their relationship through signal amplitude and the tendency of the signal shift with increasing defect angle. Our findings were validated using a tunnel magnetoresistance sensor. Future research will focus on the optimization of feature extraction complexity, considering the limited computational power available for portable non-destructive testing devices.

TIME REFRACTION and SPACETIME OPTICS

A review of recent advances in spacetime optics is given, with special emphasis on time refraction. This is a basic optical process, occurring at a temporal discontinuity or temporal boundary, which is able to produce various different effects, such as frequency shifts, energy amplification, time reflection, and photon emission. If, instead of a single discontinuity, we have two reverse temporal boundaries, we can form a temporal beam splitter, where temporal interferences can occur. It will also be shown that, in the presence of an axis of symmetry, such as a magnetic field, the temporal beam splitter can induce a rotation of the initial polarization state, similar to a Faraday rotation. Recent work on time crystals, superluminal fronts, and superfluid light will be reviewed. Time gates based on spacetime optical effects will be discussed. We also mention recent work on optical metamaterials. Finally, the quantum properties of time refraction, which imply the emission of photon from vacuum, are considered, while similar problems in high-energy QED associated with electron–positron pairs are briefly mentioned.

High-precision measurement of the magneto-optical Faraday effect via difference weak measurements

We propose a modified difference weak measurement scheme that permits precise measurements of the magneto-optical Faraday effect. By making normalized difference processing for a set of post-selected light intensity, a linear-response regime with a significant weak-value amplification effect is established. In the proof-of-principle experiment, we measure the magnetic intensity using the polarization system and achieve precision at the order of ∼10−7 T. Our scheme can be applied to measure other magneto-optical effects, providing a method for future ultra-sensitive sensing and metrology in magnetic physics.

On-chip deep subwavelength optomagnetic bistable memory based on inverse Faraday effect related nonlinearity in graphene waveguide ring resonators

Integrated optical devices that possess bistable characteristics are key elements for optical digital signal processing and all-optical computing. In this paper we report on an optomagnetic bistable memory based on the inverse Faraday effect related nonlinearity in graphene waveguide ring resonators. The effective magnetic field via the plasmon-induced inverse Faraday effect in the graphene resonator has two discrete stable states that represent logic one and logic zero and magnetic switching for memory operation can be achieved by injecting an optical pulse and momentarily blocking the bias input light. Our proposed optomagnetic bistable device based on a graphene magnetoplasmonic configuration has great potential for the development of next generation magnetic memory. It has benefits of ultrafast magnetization switching, simplicity of the considered structure, on-chip compatibility, and a deep subwavelength platform. It also enhances the nonlinear interaction due to strong confinement of the graphene plasmon modes and high-quality factor of traveling modes in the graphene ring resonator, and tunability and robustness by adjusting the gate voltages of the graphene sheets. These advantages will satisfy the demand for fast magnetization switching, low-energy consumption, and high-density recording required in future magnetic memories. Published by the American Physical Society 2024

Temperature stability analysis of the all-fiber current sensor with a loop structure

Abstract All-fiber optical current sensor (AFOCS) is a perfect product formed by the combination of fiber-optic sensing technology and the Faraday effect. It boasts significant advantages such as resistance to electromagnetic interference, a high measurement dynamic range and precision, low power consumption, low cost, and insulation. Additionally, it enables long-distance transmission, making it one of the main devices for current monitoring in smart grids. However, the birefringence within the sensing fiber is highly susceptible to changes in temperature, causing the polarization state of light to be extremely sensitive to temperature variations. This sensitivity significantly impacts the accuracy of current measurements. A novel loop structure AFOCS with a coupled fiber polarization rotator (FPR) is introduced in this paper. The operating principle of this structure is theoretically analyzed, and the Jones matrix is used to analyze the output light intensity signal and derive the error formula. After comparing the measurement accuracy of the basic AFOCS and the loop structure AFOCS, it is demonstrated that this novel structure can improve current sensitivity by enhancing the temperature robustness of the system. Additionally, the error generated by the FPR is controlled below 1%, meeting the requirements for stable system operation. Therefore, this novel structure effectively improves the accuracy of current measurement and exhibits strong temperature stability.

Response of a relativistically streaming pulsar plasma

The response tensor is derived for a relativistically streaming, strongly magnetized, one-dimensional Jüttner distribution of electrons and positrons, referred to as a pulsar plasma. This is used to produce a general treatment of wave dispersion in a pulsar plasma. Specifically, relativistic streaming, the spread in Lorentz factors in a pulsar rest frame and cyclotron resonances are taken into account. Approximations to the response tensor are derived by making approximations to relativistic plasma dispersion functions appearing in the general form of the response tensor. The cold-plasma limit, the highly relativistic limit and limits related to cyclotron resonances are considered. The theory developed in this paper has applications to generalized Faraday rotation in pulsars and magnetars.

Single-Defect-Induced Peculiarities in Inverse Faraday-Based Switching of Superconducting Current-Carrying States near a Critical Temperature

The Inverse Faraday Effect (IFE) is a phenomenon that enables non-thermal magnetization in various types of materials through the interaction with circularly polarized light. This study investigates the impact of single defects on the ability of circularly polarized radiation to switch between distinct superconducting current states, when the magnetic flux through a superconducting ring equals half the quantum flux, Φ0/2. Using both analytical methods within the standard Ginzburg–Landau theory and numerical simulations based on the stochastic time-dependent Ginzburg–Landau approach, we demonstrate that while circularly polarized light can effectively switch between current-carrying superconducting states, the presence of a single defect significantly affects this switching mechanism. We establish critical temperature conditions above which the switching effect completely disappears, offering insights into the limitations imposed by a single defect on the dynamics of light-induced IFE-based magnetization in superconductors.