Magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulators

Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator Mn Bi2Te4.We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment,Kerr and Faraday effects occur.Under perpendicular electric field,antiferromagnetic topological insulators(AFMTI)show sharp peaks at the interband transition threshold,whereas trivial insulators show small adjacent positive and negative peaks.Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators.We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr(Faraday)angles and vanishing ellipticity.Under external magnetic moment,AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity.For the qualitative behaviors,AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change.These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.

Low Gilbert damping in Bi/In-doped YIG thin films with giant Faraday effect

Magnetic films with low Gilbert damping are crucial for magnonic devices,which provide a promising platform forrealizing ultralow-energy devices.In this study,low Gilbert damping and coercive field were observed in Bi/In-dopedyttrium iron garnet(BiIn:YIG)thin films.The BiIn:YIG(444)films were deposited onto different substrates using pulsedlaser deposition.Low coercivity(<1 Oe)with saturation magnetization of 125.09 emu/cc was achieved along the in-planedirection of BiIn:YIG film.The values of Gilbert damping and inhomogeneous broadening of ferromagnetic resonance inBiIn:YIG films were obtained to be as low as 4.05×10^(-4)and 5.62 Oe,respectively.In addition to low damping,the giantFaraday rotation angles(up to 2.9×10^(4)deg/cm)were also observed in the BiIn:YIG film.By modifying the magneticstructure and coupling effect between Bi^(3+)and Fe^(3+)of Bi:YIG,doped In^(3+)plays a key role on variation of the magneticproperties.The low damping and giant Faraday effect made the BiIn:YIG film an appealing candidate for magnonic andmagneto-optical devices.

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

A narrow linewidth Faraday anomalous dispersion optical filter(FADOF)with reflection configuration is achieved for the first time based on the cesium(Cs)ground state 6S_(1/2) to the excited state 6P_(3/2) transition at 852 nm.Compared with the conventional FADOF with transmission configuration,reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters,because it allows signal light to go and return through the atomic vapor cell.In our experiment,peak transmittance at Cs 6S_(1/2) F=4-6P_(3/2) transition is 81%for the reflection-type FADOF,and while 54%for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60℃and 19 G.The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter

We demonstrate an 852-nm external cavity diode laser（ECDL） system whose wavelength is mainly determined by an interference filter instead of other wavelength selective elements. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 28.3 k Hz. Moreover, we test the application of the ECDL in the Faraday atomic filter.Besides saturated absorption spectrum, the transmission spectrum of the Faraday atomic filter at 852 nm is measured by using the ECDL. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.

Ramsey-CPT spectrum with the Faraday effect and its application to atomic clocks

A method that obtains the Ramsey-coherent population trapping （CPT） spectrum with the Faraday effect is investi- gated. An experiment is implemented to detect the light polarization components generated from the Faraday effect. The experimental results agree with the theoretical calculations based on the Liouville equation. By comparing with the method without using the Faraday effect, the potential of this method for a CPT-based atomic clock is assessed. The results indicate that this method should improve the short-term frequency stability by several times.

Gravitational Faraday effect in curved space-time induced by high-power lasers

Gravitational field produced by high-power laser is calculated according to the linearized Einstein field equation in weak field approximation. Gravitational Faraday effect of electromagnetic wave propagating in the above gravitational field is studied and the rotation angle of polarization plane of electromagnetic wave is derived. The result is discussed and estimated under the condition of present experiment facility.

Simulation of magnetization process and Faraday effect of magnetic bilayer films

We described ferromagnetic film and bilayer films composed of two ferromagnetic layers coupled through antiferromagnetic interfacial interaction by classical Heisenberg model and simulated their magnetization state,magnetic permeability,and Faraday effect at zero and finite temperature by using the Landau–Lifshitz–Gilbert(LLG)equation.The results indicate that in a microwave field with positive circular polarization,the ferromagnetic film has one resonance peak while the bilayer film has two resonance peaks.However,the resonance peak disappears in ferromagnetic film,and only one resonance peak emerges in bilayer film in the negative circularly polarized microwave field.When the microwave field’s frequency exceeds the film’s resonance frequency,the Faraday rotation angle of the ferromagnetic film is the greatest,and it decreases when the thickness of the two halves of the bilayer is reduced.When the microwave field’s frequency remains constant,the Faraday rotation angle fluctuates with temperature in the same manner as spontaneous magnetization does.When a DC magnetic field is applied in the direction of the anisotropic axis of the film,the Faraday rotation angle varies with the DC magnetic field and shows a similar shape of the hysteresis loop.

Study of magnetic and magneto-optical properties of heavily doped bismuth substitute yttrium iron garnet (Bi∶YIG) film

The magnetic and magneto-optical properties of heavily doped Bi∶YIG film were studied. The film was deposited by radio frequency magnetron sputtering method and crystallized by rapid recurrent thermal annealing (RRTA). The results show that the RRTA treated film has good properties both in microwave and optical wave band. The saturation magnetization of the film on different substrates varies from 135.7 to 138.6 kA·m-1. The coercive field of the film on GGG substrate is about 0.32 kA·m-1, while about 0.8-1.43 kA·m-1 on YAG substrate and 1.75 kA·m-1 on Al2O3 substrate. The Faraday angle is about 3-5 (°)·μm-1 when optical wavelength ranges at 450-600 nm. The transmission spectra of the Bi∶YIG films on three substrates has similar change as annealing temperature below 800 ℃. Specially, when annealing temperature is above 800 ℃ a step is observed between 550 and 650 nm wavelength for the film deposited on Al2O3 substrate.Three results are very useful in magneto-optical recording application and integrated microwave devices.

Magneto-Optic Fiber Bragg Gratings with Application to High-Resolution Magnetic Field Sensors

Magneto-optic fiber Bragg gratings （MFBG） based on magneto-optic materials have a lot of potential applications for sensing and optical signal processing. The transmission and reflection spectra of guided optical waves in the MFBG are investigated. According to the sensitivity of MFBG spectral lines to the magneto-optic coupling intensity varying with applied magnetic field, a novel magnetic field sensor of high-resolution up to 0.01 nm/（kA/m） is predicted.

Tunability of One-Dimensional Plasma Photonic Crystals with an External Magnetic Field

We investigated in detail how photonic band structures （PBSs） of one dimensional plasma photonic crystals （PPCs） are tuned after being exposed to an external magnetic field. We showed that the properties of PBSs of PPCs are tuned correspondingly because the dielectric constant of the micro plasma layer is modified differently in different frequency ranges due to magneto-optical effects. Two numerical cases are calculated and discussed to study the magneto-optical effects on the properties of PBSs, including the Faraday and Voigt effects.

Recent Progress of the HL-2A Multi-Channel HCOOH Laser Interferometer/Polarimeter

A multichannel methanoic acid （HCOOH, λ=432.5 μm） laser interferometer/polarimeter is being developed from the previous eight-channel hydrogen cyanide （HCN, λ=337 μm） laser interferometer in the HL-2A tokamak. A conventional Michelson-type interometer is used for the electron density measurement, and a Dodel-Kunz-type polarimeter is used for the Faraday rotation effect measurement, respectively. Each HCOOH laser can produce a linearly polarized radiation at a power lever of -30 mW, and a power stability 〈10% in 50 rain. A beam waist （diameter d0 ≈12.0 mm, about 200 mm away from the outlet） is finally determined through a chopping modulation technique. The latest optical layout of the interferometer/polarimeter has been finished, and the hardware data processing system based on the fast Fourier transform phase- comparator technique is being explored. In order to demonstrate the feasibility of the diagnostic scheme, two associated bench simulation experiments were carried out in the laboratory, in which the plasma was simulated by a piece of polytetrafluoroethene plate, and the Faraday rotation effect was simulated by a rotating half-wave plate. Simulation results agreed well with the initial experimental conditions. At present, the HCOOH laser interferometer/polarimeter system is being assembled on HL-2A, and is planned to be applied in the 2014-2015 experimental campaign.

Principle of adaptive optical current transducer on independent variables and its test

In order to improve the measurement precision of the optical current transducer （ OCT）, the adaptive optical transducing principle on independent variables is presented in this paper. And one of the adaptive optical current transducer（AOCT） on the independent variables of the output of the electricmegnet current transducer is introduced. According to IEC660044-8, the performance of AOCT was examined roundly applying the standard testing system authenticated by the state authority. The results indicate that the measurement precision of the AOCT has already reached 0. 2 class under the temperature from -40℃ to 60℃ ,which proves the feasibility of the method.

Magneto－optic Current Sensor Based on Total Reflections in a Quadrangular Bulk Glass

A novel optical device of a bulk glass Faraday current sensor is presented,which has a accuracy of 0. 5 in the current region of 1 000- 8 000 A and over a temperature range from-30℃ to + 40℃. The new sensing device can compensate the phase difference between p and s components of the incident light caused by total internal reflections in a glass. The self-correction, auto-correlation and auto-amplification techniques are used in the signal treatment with the help of a computer.

A Passive Optical Fiber Current Sensor Based on YIG

A research on passive optical fiber current sensor based on magneto-optical crystal and a new design of light path of the sensor head are presented. Both methods of dual-channel optical detection of the polarization state of the output light and signal processing are proposed. Signal processing can obtain the linear output of the current measurement of the wire more conveniently. Theoretical analysis on the magnetooptical fiber current sensor is given, followed by experiments. After that, further analysis is made according to the results, which leads to clarifying the exiting problems and their placements.

2.32W anti-misaligned Er:LuAG single-longitudinal-mode laser in the double corner-cube-retroreflector resonator and MOPA system

We demonstrate a high power,Er:Lu AG single-longitudinal-mode laser in an anti-misaligned resonator.Based on the Faraday effect,a 1.61 W single-longitudinal-mode(SLM)laser is obtained with the double corner-cube-retroreflector(CCR)structure,and the tunable wavelength is 1649.2-1650.3 nm.Additionally,we investigate the anti-misalignment characteristics when the CCR moves and rotates along the optical axis.Furthermore,by utilizing the Er:Lu AG amplifier,the maximum 2.32 W single-longitudinal-mode laser at 1649.6 nm is achieved.The beam quality factors M^(2) of the 2.32 W Er:Lu AG single-longitudinal-mode laser are 1.23 and 1.25 along the horizontal(x)and vertical(y)directions,respectively.

Optical Sensor with Wide Range and High Sensitivity for Internal Magnetic Field Detection of Transformer

The deterioration of winding defects is one of the important causes of power transformer fires and even explosion failures.The change of leakage magnetic field distribution is the most direct response to winding defects.Currently there are few sensors suitable for online measurement of the internal magnetic field of transformers.Based on the Faraday magneto-optical effect,a magnetic field sensor with wide range and high sensitivity is proposed in this paper,which is suitable for the interior use of transformers.The straight-through optical structure with interior polarizer is adopted,and the sensor has a measurement range of 1.5 T and a sensitivity of 1 mT.It also possesses a small size,with a length of about 30 mm after encapsulation.The influence mechanism of vibration and temperature is revealed through theoretical analysis and numerical simulation.It is proposed to filter out the interference of vibration by characteristic frequency analysis and to compensate for temperature by a two-probe structure.An anti-interference test verifies the effectiveness of this method,and it can reduce the error from 80.56%to 2.63%under the combined interference of vibration and temperature.

Ultranarrow bandwidth Faraday atomic filter approaching natural linewidth based on cold atoms

An ultranarrow bandwidth Faraday atomic filter is realized based on cold 87Rb atoms. The atomic filter operates at 780 nm on the 52 S1/2, F = 2 to 52 P3/2, F’= 3 transition with a bandwidth of 7.1(8) MHz, which is approaching the natural linewidth of the transition. The peak transmission achieves 2.6(3)% by the multi-pass probe method. This atomic filter based on cold atoms may find potential applications in self-stabilizing lasers in the future.

Mossbauer Faraday Effect in Fe_3O_4

We have observed the Mossbauer Faraday effect in nonstoichiometric Fe_3O_4 by the Mossbauer polarimeter. Experimental results demonstrate that the electronic hopping above Verwey temperature within Fe^(2+)-Fe^(3+) ions on the octahedral sites is only a localized phenomenon and the recoilless fractions of ^(57)Fe nuclei in Fe_(3-0.02v)O_4 are 0.71 for A sites and 0.62 for B sites, respectively.

Faraday effect measurements of holmium oxide(Ho2O3) ceramics-based magneto-optical materials

Faraday effect measurements of holmium oxide(Ho_2O_3) ceramics-based magneto-optical materials, highly potential material candidates for high-energy laser Faraday isolators, are presented in this paper. Temperature dependence of the Verdet constant of nondoped Ho_2O_3 ceramics was measured for temperatures 15–305 K at 1.064 μm wavelength.The Verdet constant dispersion for wavelengths 0.5–1 μm and 1.064 μm was measured for both nondoped Ho_2O_3 ceramics and Ho_2O_3 ceramics doped with terbium Tb3+(0.2 at. %) and cerium Ce3+(0.1 at. %) ions. The results suggest that the relatively low level of doping of Ho_2O_3 with these ions has no significant boosting impact on the Faraday effect. Therefore, other compositions of Ho_2O_3 ceramics-based magneto-optical materials, as well as various doping concentrations, should be further examined.

Distributed parametric modeling and simulation of light polarization states using magneto-optical sensing based on the Faraday effect

To solve the problems encountered in practical processes of magneto-optical sensing, the infinitesimal distributed-parameter model and finite-element accumulation of different dielectric properties of micromaterials were used to describe the evolution of light polarization states, instead of the previously commonly used method of lumped-parameter simulation, thus essentially explaining the mechanism of sensing, magneto-optical effects, and related factors, and achieving multiphysics coupling using the COMSOL finite-element analysis method. Considering the cases of the Faraday effect without and with line birefringence, the magneto-optical effect and output characteristics of an infinitesimal magneto-optical sensor were simulated and studied. The results verified the effectiveness of the infinitesimal sensor model. Because the magnetic field, stress, and temperature changes alter the dielectric properties of magneto-optical materials, the finite-element accumulation method lays a good foundation for research on theoretical analysis and performance of magneto-optical sensors affected by factors such as the magnetic field, temperature, and stress.