Magnetic Birefringence Research Articles

Study of the birefringence noise in high-finesse ULE cavity

High-finesse ultra-low expansion (ULE) cavities are important components in many precision optical experiments, and the cavity length noise in ULE cavities has been intensively studied. However, some experiments, such as vacuum magnetic birefringence measurements, have focused on the phase difference between orthogonal polarizations. To determine the effect of high-reflectivity mirrors on birefringence noise, we investigated the birefringence noise of a ULE cavity with the finesse of 531000(1000) and obtained the noise spectrum of the intrinsic birefringence of the cavity. The single-pass phase difference due to the birefringence of the cavity mirror is (21.3±0.2)μrad and the noise for the birefringent cavity is 81.3prad/Hz at 0.1Hz and 2.6prad/Hz at 40Hz. These results may draw attention when considering noise in cavity-based optical experiments.

Magnetic field induced isotropic ferrofluid to ferronematic phase transition in thermotropic liquid crystal

Experiments on liquid crystals doped with ferromagnetic nanoparticles predicted the isotropic ferrofluid to ferronematic phase transition. The magnetic field induced isotropic ferrofluid to ferronematic phase transition in thermotropic liquid crystal has been studied theoretically. Theoretical model is based on Flory–Huggins theory of isotropic mixing and Landau-de Gennes theory. The impact of ferromagnetic nanoparticles and magnetic field on the isotropic ferrofluid to ferronematic phase transition and transition temperature has been discussed. Theoretical results predict the magnetic field induced critical point of the isotropic ferrofluid to ferronematic phase transition. The temperature and volume fraction of ferromagnetic nanoparticles dependence of the magnetic birefringence and Cotton-Mouton constant are calculated.

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.

The average magnetic anisotropy of polystyrene in polymersomes self-assembled from poly(ethylene glycol)-b-polystyrene.

Using the diamagnetic anisotropy of polymers for the characterization of polymers and polymer aggregates is a relatively new approach in the field of soft-matter and polymer research. So far, a good and thorough quantitative description of these diamagnetic properties has been lacking. Using a simple equation that links the magnetic properties of an average polymer repeating unit to those of the polymer vesicle of any shape, we measured, using magnetic birefringence, the average diamagnetic anisotropy of a polystyrene (PS) repeating unit, ΔχPS, inside a poly(ethylene glycol)-polystyrene (PEG-PS) polymersome membrane as a function of the PS-length and as a function of the preparation method. All obtained values of ΔχPS have a negative sign which results in polymers tending to align perpendicular to an applied magnetic field. Combined, the same order of magnitude of ΔχPS (10-12 m3 mol-1) for all polymersome shapes proves that the individual polymers are organized similarly regardless of the PS length and polymersome shape. Furthermore, the value found is only a fraction (∼1%) of what it can maximally be due to the random coiling of the polymers. We, therefore, predict that further ordering of the polymers within the membrane could lead to similar responses at much lower magnetic fields, possibly obtainable with permanent magnets, which would be highly advantageous for practical applications.

Simultaneous measurement of polarization rotation angle and ellipticity at the quantum noise limit

An experiment has been proposed for laser polarization signal measurement, with the rotation angle and ellipticity being measured simultaneously. The proposed experiment is immune to signal-to-noise ratio degradation due to the finite extinction ratio of polarizing elements used to construct the composite polarization measurement setup. Noise analysis is carried out to show that the proposed scheme allows one to reach the quantum noise limit in the simultaneous measurement of the polarization angle and ellipticity. This work should be of great interest for experiments such as observation of vacuum magnetic birefringence, spin-orbital interaction, material characterization, polarization microscopy, or biomedical optics.

Minimal length corrections to magnetic birefringence in vacuum

Minimal length corrections to magnetic birefringence in vacuum

Effects of wave propagation in canonical Poisson gauge theory under an external magnetic field

The non-commutative electrodynamics based on the canonical Poisson gauge theory is studied in this paper. For a pure spatial non-commutativity, we investigate the plane wave solutions in the presence of a constant and uniform magnetic background field for the classical electrodynamics in canonical Poisson gauge theory. We obtain the properties of the medium ruled by the permittivity and the permeability tensors in terms of the non-commutative parameter, with the electrodynamics equations in the momentum space. Using the plane wave solutions mentioned, the dispersion relations are modified by the magnetic background, and the correspondent group velocity is affected by the spatial non-commutative parameter. We construct the energy-momentum tensor and discuss the conserved components of this tensor in the spatial non-commutative case. The birefringence phenomenon is showed through the modified dispersion relations, that depends directly on the non-commutative corrections and also on the magnetic background field. Using the bound of the polarized vacuum with laser (PVLAS) experiment for the vacuum magnetic birefringence, we estimate a theoretical value for the spatial non-commutative parameter.

Liquid Crystalline Magneto-Optically Active Peralkylated Azacoronene.

Organic Faraday rotators have gained significant attention in recent years as a promising alternative to traditional inorganic magneto-optical (MO) materials as a result of their lower cost, superior mechanical properties, and potential for large-scale deployment. This interest is peaked by the fact that a number of high symmetry, rigid, strongly optically absorbing organic chromophores display Verdet constants an order of magnitude higher than commercial inorganic Faraday rotators. Critical to the development of new generations of organic materials is the ability to organize them in optimal structures for optical coupling/measurements. We report herein the synthesis of a dodecyl-substituted hexapyrrolohexaazacoronene (C12-HPHAC) displaying discotic liquid crystalline (LC) properties and large Faraday rotation. Thin films with a redox mixed C12-HPHAC/C12-HPHAC+2 composition display a discotic columnar LC phase, are stable to air and moisture in the solid and solution states, and achieve a maximum Verdet constant of 3.36 × 105 deg T-1 m-1 at 700 nm. This result is consistent with Serber's model of magnetic circular birefringence and displays one of the largest reported Verdet constants for organic materials in the UV-Vis range. The LC phase aligns the molecules and leads to gains in Verdet constants of up to 105% through the favorable orientation of the molecules' magnetic and electric transition dipole moments with respect to the applied magnetic field.

Observation of the Strong Magneto-Optical Rotation of the Polarization of Light in Rubidium Vapor for Applications in Atomic Magnetometry

Nonlinear resonances in alkali metal vapor, which are detected by the magneto-optical rotation of the linear polarization of light, are actively used in quantum magnetometry to fabricate atomic magnetometers. The magneto-optical rotation in most such sensors is due to magnetic birefringence, and rotation angles usually do not exceed tens of milliradians. In this work, an experiment where magneto-optical resonances of linear polarization rotation of a probe wave are due to strong dichroism induced in a medium by a counterpropagating pump wave has been proposed. Both waves are in resonance with the Fg = 2 → Fe = 1 optical transition in the 87Rb D1 line (λ ≈ 795 nm). Experiments have been carried out with a 2-cm-long cylindrical cell filled with a buffer gas, and the maximum rotation angle is ≈390 mrad (22°) at a width of resonance of about 300 nT. The results show that the configuration proposed for the observation of magneto-optical rotation is promising for the fabrication of compact high-sensitivity atomic magnetometers.

Observation of the Strong Magneto-Optical Rotation of the Polarization of Light in Rubidium Vapor for Applications in Atomic Magnetometry

Nonlinear resonances in alkali metal vapor, which are detected by the magneto-optical rotation of the linear polarization of light, are actively used in quantum magnetometry to fabricate atomic magnetometers. The magneto-optical rotation in most such sensors is due to magnetic birefringence, and rotation angles usually do not exceed tens of milliradians. In this work, an experiment where magneto-optical resonances of linear polarization rotation of a probe wave are due to strong dichroism induced in a medium by a counterpropagating pump wave has been proposed. Both waves are in resonance with the Fg = 2 → Fe = 1 optical transition in the 87Rb D1 line (λ ≈ 795 nm). Experiments have been carried out with a 2-cm-long cylindrical cell filled with a buffer gas, and the maximum rotation angle is ≈390 mrad (22°) at a width of resonance of about 300 nT. The results show that the configuration proposed for the observation of magneto-optical rotation is promising for the fabrication of compact high-sensitivity atomic magnetometers.

Spectra of the Effects of Magnetic Birefringence and Dichroism in Magnetic Colloids with Different Particle Sizes

Spectra of the Effects of Magnetic Birefringence and Dichroism in Magnetic Colloids with Different Particle Sizes

Spectra of the effects of magnetic birefringence and dichroism in magnetic colloids with different particle sizes

Experimental studies of the spectral dependences of the effects of birefringence and dichroism in magnetic colloids with magnetite nanoparticles with an average size of 5.5 and 8 nm have been carried out. It is shown that the magnitude of the effects in a sample with larger particles is approximately two times greater at the same volume concentration. Possible reasons for this difference are analyzed, considering the polydispersity of the samples, as well as the possibility of the presence of magnetically hard and superparamagnetic particles in them. The calculations of the spectra of the effects of birefringence and dichroism showed good agreement with the experimental data.

Effect of antiferromagnetic order on a propagating single-cycle THz pulse

Employing polarization sensitive terahertz (THz) transmission spectroscopy, we explored how the waveform of initially single-cycle linearly polarized THz pulses changes upon propagation through a thick antiferromagnetic crystal of CoF2. The changes upon propagation through CoF2 are found to depend strongly on both the incoming polarization and temperature. In particular, the ellipticity and polarization rotation acquired by initially linearly polarized light are quantified and explained in terms of magnetic linear birefringence and dichroism. Although the magneto-optical effects are often considered to be relatively weak, our experiments reveal that the polarization of the THz pulse substantially changes along the pulse duration. The pulse shape is further complicated by features assigned to the formation of magnon-polaritons. The findings clearly show the importance of accounting for propagation effects in antiferromagnetic spintronics and magnonics.

Quantum theory of cross correlation heterodyne detection

Cross correlation heterodyne detectors exhibit the potential for suppression of the detection quantum noise below shot noise without use of optical squeezing for capturing weak optical signals in low frequency bands. To understand the underlying mechanism, we develop a quantum theory to describe the noise performance of cross correlation heterodyne detectors. By calculating the cross spectral density (CSD) of the photocurrent fluctuations from a cross correlation heterodyne detector, we prove that its noise performance can break the shot noise limit and exceed that of a regular heterodyne detector for detection of coherent light. When the detected light signal is in a squeezed state, we show that the corresponding CSD value is negative and discuss how a negative CSD may be explored to improve the output signal-to-noise ratio of the detector contaminated by classical noises through tuning the parameter of the degree of squeezing. This work may find itself useful in space-based gravitational wave searching and a variety of other scientific research activities, such as observation of vacuum magnetic birefringence and telecommunications.

First- and second-order magneto-optical effects and intrinsically anomalous transport in the two-dimensional van der Waals layered magnets CrXY (X=S,Se,Te;Y=Cl,Br,I)

Recently, the two-dimensional magnetic semiconductor CrSBr has attracted considerable attention due to its excellent air-stable property and high magnetic critical temperature. Here, we systematically investigate the electronic structure, magnetocrystalline anisotropy energy, first-order magneto-optical effects (Kerr and Faraday effects), and second-order magneto-optical effects (Sch\"afer-Hubert and Voigt effects) as well as intrinsically anomalous transport properties (anomalous Hall, anomalous Nernst, and anomalous thermal Hall effects) of two-dimensional van der Waals layered magnets $\mathrm{Cr}\mathit{XY} (X=\mathrm{S},\mathrm{Se},\mathrm{Te};Y=\mathrm{Cl},\mathrm{Br},\mathrm{I})$ by using first-principles calculations. Our results show that monolayer and bilayer $\mathrm{Cr}\mathit{XY} (X=\mathrm{S},\mathrm{Se})$ are narrow-band-gap semiconductors, whereas monolayer and bilayer $\mathrm{CrTe}Y$ are multiband metals. The magnetic ground states of bilayer $\mathrm{Cr}\mathit{XY}$ and the easy magnetization axis of monolayer and bilayer $\mathrm{Cr}\mathit{XY}$ are confirmed by the magnetocrystalline anisotropy energy calculations. Utilizing magnetic group theory analysis, the first-order magneto-optical effects as well as anomalous Hall, anomalous Nernst, and anomalous thermal Hall effects are identified to exist in a ferromagnetic state with out-of-plane magnetization. The second-order magneto-optical effects are not restricted by the above symmetry requirements, and therefore they can arise in ferromagnetic and antiferromagnetic states with in-plane magnetization. The calculated results are compared with the available theoretical and experimental data of other two-dimensional magnets and some conventional ferromagnets. The present work reveals that monolayer and bilayer $\mathrm{Cr}\mathit{XY}$ with superior magneto-optical responses and anomalous transport properties provide an excellent material platform for the promising applications of magneto-optical devices, spintronics, and spin caloritronics.

Self-temperature compensation approach for fiber specklegram magnetic field sensor based on polarization specklegram analysis

A self-temperature compensation method based on polarization specklegram analysis and magnetic birefringence effect of magnetic fluid (MF) is proposed for a fiber speckle sensor (FSS). The temperature compensation is achieved by measuring the variation difference of the two specklegrams with vertical linear polarization state. A fiber specklegram magnetic field sensor has been designed with this method and the magnetic-birefringence effect of MF. The measurement of magnetic field with high stability and good repeatability has been successfully achieved, which demonstrates the effectiveness of the proposed method. Due to the merits of low cost, ease of implement and system simplicity, the proposed method can promote the practical use of the FSS in long term monitoring.

Laser-induced THz magnetism of antiferromagnetic CoF2

Excitation, detection, and control of coherent THz magnetic excitation in antiferromagnets are challenging problems that can be addressed using ever shorter laser pulses. We study experimentally excitation of magnetic dynamics at THz frequencies in an antiferromagnetic insulator CoF2 by sub-10 fs laser pulses. Time-resolved pump-probe polarimetric measurements at different temperatures and probe polarizations reveal laser-induced transient circular birefringence oscillating at the frequency of 7.45 THz and present below the Néel temperature. The THz oscillations of circular birefringence are ascribed to oscillations of the magnetic moments of Co2+ ions induced by the laser-driven coherent E g phonon mode via the THz analogue of the transverse piezomagnetic effect. It is also shown that the same pulse launches coherent oscillations of the magnetic linear birefringence at the frequency of 3.4 THz corresponding to the two-magnon mode. Analysis of the probe polarization dependence of the transient magnetic linear birefringence at the frequency of the two-magnon mode enables identifying its symmetry.

Magneto-optical study of metamagnetic transitions in the antiferromagnetic phase of \u03b1-RuCl3

α-RuCl3 is a promising candidate material to realize the so far elusive quantum spin liquid ground state. However, at low temperatures, the coexistence of different exchange interactions couple the effective pseudospins into an antiferromagnetically zigzag (ZZ) ordered state. The low-field evolution of spin structure is still a matter of debate and the magnetic anisotropy within the honeycomb planes is an open and challenging question. Here, we investigate the evolution of the ZZ order parameter by second-order magneto-optical effects, the magnetic linear dichroism and magnetic linear birefringence. Our results clarify the presence and nature of metamagnetic transitions in the ZZ phase of α-RuCl3. The experimental observations show the presence of initial magnetic domain repopulation followed by a spin-flop transition for small in-plane applied magnetic fields (≈1.6 T) along specific crystallographic directions. In addition, using a magneto-optical approach, we detected the recently reported emergence of a field-induced intermediate phase before suppressing the ZZ order. The results disclose the details of various angle-dependent in-plane metamagnetic transitions quantifying the bond-anisotropic interactions present in α-RuCl3.

Magnetic birefringence of montmorillonite dispersion

Compared with unadulterated polymers, filler/polymer composites can exhibit superior properties. Modulating the orientation of montmorillonite (MMT) filler may maximize this filler’s properties in shape-anisotropic applications. We measured the magnetic birefringence of MMT dispersions in water with custom magnetic birefringence equipment and estimated the inherent birefringence and anisotropic magnetic susceptibility of MMT. We classified polydisperse MMT to prepare MMT dispersions with a narrow size distribution. From the relationship between the retardation obtained by magnetic birefringence measurements and the reciprocal of the square of the magnetic field, we estimated the inherent birefringence of MMT to be −0.060. Considering the size distribution, and by setting the anisotropic magnetic susceptibility to −1.5 × 10−5, we reproduced the magnetic flux density dependence of the magnetic birefringence of MMT with a particle size of ≤300 nm.

Polarimetry for measuring the vacuum magnetic birefringence with quasi-static fields: a systematics study for the VMB@CERN experiment

We present an experimental systematics study of a polarimetric method for measuring the vacuum magnetic birefringence based on a pair of rotating half-wave plates. The presence of a systematic effect at the same frequency as the sought for magneto-optical effect inhibits the use of strictly constant magnetic fields. We characterise this systematic, discuss its origin and propose a viable workaround.