Magneto-optical Control Research Articles

Evaluation of the characteristics of ferrite garnet films for magneto-optical control of materials

A setup based on a polarization microscope was developed to study the characteristics of two types of ferrite-garnet films with the chemical composition Lu1.51Ho0.56Bi0.93Fe4.1Al0.9O12. The parameters of the hysteresis loop, values of residual magnetization, and the saturation field of the studied films were determined experimentally. The domain structure period was estab-lished, and a compact device for visualizing defects in steel samples was created. Using this device, a series of experiments were conducted on test samples with cracks of various sizes, and magneto-optical images of the cracks were obtained. The hysteresis loop of the two types of ferrite-garnet films was constructed in the “magnetiza-tion coefficient-magnetic field induction” coordinates. The magnetization coefficient was cal-culated based on the relative change in the area of bright and dark domains when the external magnetic field, directed perpendicular to the film plane, was varied. The efficiency of using two types of films, grown under different technological conditions but having the same chemical composition, in non-destructive testing methods was analyzed. It was found that the investigated films had the same domain period, but their residual magnetization and saturation field values varied significantly. Diagrams of the experimental setup and the developed device, as well as the characteristics of some of their components, are presented. To generate the magnetic field in the test samples, a coil wound on a U-shaped ferrite core was used, pressed against the sample surface on the opposite side relative to the crack location. The experiments were conducted under constant magnetic fields of varying intensity. The device was tested on specially prepared test samples with pre-grown cracks of known sizes. The tests demonstrated that films with higher residual magnetization and saturation field values were more sensitive to detecting defects such as enclosed cracks.

Magneto-optical induced supermode switching in quantum fluids of light

The insensitivity of photons towards external magnetic fields forms one of the hardest barriers against efficient magneto-optical control, aiming at modulating the polarization state of light. However, there is even scarcer evidence of magneto-optical effects that can spatially modulate light. Here, we demonstrate the latter by exploiting strongly coupled states of semimagnetic matter and light in planar semiconductor microcavities. We nonresonantly excite two spatially adjacent exciton-polariton condensates which, through inherent ballistic near field coupling mechanism, spontaneously synchronise into a dissipative quantum fluidic supermode of definite parity. Applying a magnetic field along the optical axis, we continuously adjust the light-matter composition of the condensate exciton-polaritons, inducing a supermode switch into a higher order mode of opposite parity. Our findings set the ground towards magnetic spatial modulation of nonlinear light.

Optimal photon-magnon mode matching in whispering-gallery mode cavities.

Optomagnonic structures are widely studied in the field of nanophotonics and quantum information science. They are the key platforms for the realization of magnon-mediated microwave to optical transducers in various applications of quantum computing. In order to enhance the coupling between light (photons) and spin waves (magnons), here in this work, we use the Lagrange multiplication method to find the optimum matching condition between the optical whispering-gallery mode and the magnon with Kittle and higher-order modes in microresonators. It is found that the magnon modes located near the edge of the resonator exhibits stronger coupling strength with the optical modes. Numerically, we find the coupling constant can approach 87.6×2π H z in Kittle mode, and 459×2π H z in high-order magnon mode for a yttrium iron garnet (YIG, Y3Fe5O12 ) microdisk cavity with a radius of 300 microns and a thickness of 10 microns. We believe these results may provide an efficient way for enhancing the magneto-optical interaction in the optical devices, which will facilitate the development of magneto-optical control, optical-microwave interaction, and optical nonlinearity.

Magneto-Optical Control of Radiation in Photonic Crystal Structures via the Excitation of Surface Modes

It is shown that the intensity of magneto-optical effects is enhanced by structures containing photonic crystal layers and an iron garnet ferromagnetic dielectric as they support the excitation of quasi-surface Tamm modes at the boundary between the two. Such structures have high Q-factor resonances and can enhance the transverse magneto-optical Kerr effect. Up to 100% magneto-optical modulation can be achieved due to near-surface localization of the electromagnetic field.

Optical bistability and self-opacity in magnetically doped monolayer transition metal dichalcogenides

Magneto-optical control of optical absorption spectra is theoretically investigated in two-dimensional (2D) dilute magnetic semiconductors such as monolayer transition metal dichalcogenides (TMDs) doped with magnetic ions. The underlying mechanism relies on efficient spin transfer between spin-polarized photoexcited carriers and localized magnetic ions via exchange scattering, and subsequent shifts in the electronic band structure induced by the resulting time-reversal symmetry breaking. A self-consistent model based on a rate equation is developed to analyze dynamical polarization of itinerant carrier spins and localized magnetic moments under circularly polarized optical excitation and the corresponding band modifications. The results illustrate that nonlinear effects such as optical bistability and self-opacity can indeed be achieved efficiently for a range of excitation power and frequency. In particular, the addition of magnetic dopants is shown to reduce the optical power required for the necessary band shifts by four orders of magnitude compared to that via the optical Stark effect in a nonmagnetic counterpart. Further investigation in a multidimensional parameter space elucidates the conditions for practical realization of the desired nonlinear effects in 2D TMD monolayers.

Magneto-optical control and spin coupling with non-reciprocal surface waves for nanoscale thermotronics -INVITED

Magneto-optical materials have been proposed as promising candidates for an active control of the directionality of nanoscale heat radiation. Here, we discuss the possibility to rectify nanoscale radiative heat fluxes by means of non-reciprocal surface waves and propose a nanoscale heat flux rectifier or diode which can be controlled actively by means of externally applied fields. We furthermore, reveal the spin coupling mechanism behind the observed heat flux rectification

Active Magneto-Optical Control of Near-Field Radiative Heat Transfer between Graphene Sheets

Graphene provides an ideal platform for active modulation of near-field radiative heat transfer. While much research here focuses on tuning the chemical potential by doping or gating, this work proposes using a magnetic field to control near-field heat flux between graphene sheets. The authors predict giant thermal magnetoresistance and negative thermal magnetoresistance of the near-field radiative heat flux for different Fermi energies, and Shubnikov-de-Haas-like oscillations in the spectral heat flux. In a static magnetic field, coupling of excited magnetoplasmon-polariton modes of graphene boosts radiative heat transfer beyond the blackbody limit by several orders of magnitude.

Magneto-optical control decoupled from the optical response in magnetic metallic gratings

Structured metallic and magnetic materials have attracted increasing attention due to their potential for label-free molecular detection, based on the control of the phase of light. Traditionally, tuning magneto-optical signals via magnetoplasmon leads to an excessively low light energy at the critical position in the spectrum. Thus, improving the reflectivity of magnetoplasmon-based photonic devices is a promising method to enhance their environmental adaptability. Here, we introduce a strategy for decoupling magneto-optical signal control and modulation of the reflection spectral line shape in ferromagnetic metallic gratings. This strategy is based on the sensibility of metallic gratings to the incident polarization state and the conclusion that the spin-orbit coupling induced orthogonal plasmon mode can be treated as from a pseudolight source. The decoupling and other phenomena of the oft-repeated magneto-optical Kerr rotation reversals and sensitivity to incident angle are validated using a cobalt grating.

Magneto-optical control of Imbert–Fedorov shifts of a light beam reflected from interfaced monolayer graphene

We theoretically investigate the Imbert–Fedorov (IF) shifts of a reflected light beam from the dielectric interface containing a planar anisotropic monolayer graphene sheet that is subject to an external perpendicular magnetic field. We calculate and discuss the dependence of the IF shifts on the intensity of the magnetic field, the incidence angle of the beam, and the central frequency of the beam. It is shown that IF shifts can be controlled by modifying the intensity of the magnetic field and the incidence angle without changing the material and the structure of the dielectric interface. Moreover, there exists an optimum nonzero control magnetic field under which the IF shift can reach maximum value.

Active magneto-optical control of spontaneous emission in graphene

We investigate the spontaneous emission rate of a two-level quantum emitter near a graphene-coated substrate under the influence of an external magnetic field or strain induced pseudo-magnetic field. We demonstrate that the application of the magnetic field can substantially increase or decrease the decay rate. We show that a suppression as large as 99$\%$ in the Purcell factor is achieved even for moderate magnetic fields. The emitter's lifetime is a discontinuous function of $|{\bf B}|$, which is a direct consequence of the occurrence of discrete Landau levels in graphene. We demonstrate that, in the near-field regime, the magnetic field enables an unprecedented control of the decay pathways into which the photon/polariton can be emitted. Our findings strongly suggest that a magnetic field could act as an efficient agent for on-demand, active control of light-matter interactions in graphene at the quantum level.

Magneto-optical switching and routing via coherently induced photonic band gaps in a driven Fe = 0↔Fg = 1 transition

In an Fe = 0↔Fg = 1 transition interacting with a weak π-polarized probe and a strong σ-polarized standing-wave coupling, we obtain single or double photonic band gaps depending on the applied magnetic field. Moreover, the coherently induced two-photonic-band gap structure can be tuned by the magnitude of the magnetic field. Such a magnetic-field-dependent feature is exploited to devise magneto-optical switching and routing of two light pulses. The efficient magneto-optical control of light propagation may have applications in an optical network and optical information processing.

Temporal solitons in magnetooptic and metamaterial waveguides

The important topic of temporal soliton propagation in double-negative metamaterials is discussed with an emphasis upon short pulses that exhibit self-steepening controlled by the frequency dependence of the relative permittivity and permeability. In addition, magnetooptic control is included, leading to some fascinating outcomes that should have practical application. The role of self-steepening, Raman scattering, third-order dispersion and magnetooptics is thoroughly investigated, and it is shown that pulses can acquire signatures in the form of additional velocities with respect to the moving frame. The metamaterial influence upon self-steepening has such a strong frequency dependence that it can be used to combat Raman scattering. The self-steepening can change sign, and it is shown that it is possible to arrange pulses in special switching formats to organise the output times. The metamaterial influence upon bit-patterns admits an important degree of control over multi-pulse interactions, and this is combined with magnetooptics to restore patterns. The role of third-order dispersion is also presented. Again, a control of the pulse behaviour in the neighbourhood where the frequency dependence causes the group-velocity dispersion parameter to approach zero is a direct consequence of using this kind of metamaterial. Finally, a Lagrangian analysis is used to support simulations of the positions of the pulse maxima.

Magneto-optical control of the group velocity of light in an inhomogeneously broadened medium

We investigate the use of a magnetic field, in conjunction with an elliptically polarized laser field, to control the group velocity of light in an inhomogeneously broadened medium. We show both theoretically and experimentally that the dispersion and hence, the speed of light in an atomic system, having V-configuration with Zeeman sublevels as their excited states, can be effectively controlled magneto-optically. We present approximate analytical solutions for a homogeneously broadened medium and numerical solutions for both a homogeneously and an inhomogeneously broadened medium. We show that while one can tune the speed of light from subluminal to superluminal with the magnetic field in a static or cooled medium with V-type atoms, in hot atoms one can achieve an efficient magneto-optical tunability in the subluminal regime. We experimentally demonstrate such control of light speed using a single elliptically polarized light and a moderately strong magnetic field in a 87Rb vapor cell. We propose to use the optical field for coarse control and the magnetic field for finer control of the light speed in an atomic medium.

Magneto-optical control of atomic spin mixing in dipolar spinor Bose-Einstein condensates

We study the role in an external photoassociation light field in the spin mixing dynamics of a spin-one Bose condensate with long-range magnetic dipole-dipole interaction. The mean-field energy functional of the system is found to be formally identical to that of two coupled nonrigid pendulums, manifesting either constructive or destructive interferences. The interplay between photoassociation and the magnetic dipole-dipole interaction provides a novel route to the magneto-optical quantum control of atomic spin mixing in dipolar spinor condensates.

Bright spatial solitons in controlled negative phase metamaterials

A fundamental discussion of linearly polarised bright spatial soliton beams that are localised in a planar waveguide is developed in a special way that leads to the introduction of nonlinear diffraction. It is emphasised, throughout, that this kind of diffraction dominates influences from non-paraxiality and typical quintic contributions to the nonlinearity. A major discussion is given that is based upon double-negative metamaterials and makes contact with previous literature. Both homogeneous and inhomogeneous diffraction-managed, planar waveguides are investigated with a view to examining the behaviour of narrow beam production and propagation. It is also shown that a Voigt configuration of an externally applied magnetic field can be used to create significant magnetooptic control over spatial soliton propagation in asymmetric waveguides. Both this type of control and diffraction-management lie at the heart of the numerical simulations given here. In all of these cases it is shown that nonlinear diffraction has a very important influence and will create an impact upon future applications.

Magneto-optical Control of Light Collapse in Bulk Kerr Media

The Cotton-Mouton (Voigt) and Faraday effects induce adjustable linear and circular birefringence in optical media with external magnetic fields. We consider these effects as a technique for magneto-optical control of the transmission of bimodal light beams through Kerr-nonlinear crystals. Numerical analysis suggests that a properly applied magnetic field may accelerate, delay, or arrest the collapse of (2+1)D beams. Experimentally, the magnetic collapse acceleration is demonstrated in a bulk yttrium iron garnet (YIG) crystal.

Ring gas lasers with magneto-optical control for laser gyroscopy (invited paper)

The main physical principles of the operation of ring gas lasers in the laser-gyroscope regime are examined. The influence of nonreciprocal effects on the operational parameters of ring gas lasers and the methods of controlling, with the aid of the nonreciprocal magneto-optical Zeeman effect, the parameters of these lasers used in gyroscopes are discussed.

Magneto-Optical Control for Frequency Scanning in Patch Antenna Array

A novel technique is proposed for frequency scanning using active patch antenna array on ferrite substrate. The system consists of a FET oscillator integrated to the array elements via amplifiers. The oscillator can be optically tuned over a band of frequency to which the antennas can also be tuned by proper magnetic biasing of the substrate. A system description with predicted and observed performance is presented.

Intracavity magnetooptical control of the intensity of the radiation of a gas laser with a high-gain active medium

In connection with the possibility of intracavity polarization control of the intensity of radiation [5, 6], it is of great interest to study also the energy characteristics of a laser whose cavity contains both amplitude and circular phase anisotropy. In spite of the fact that the intensity of the radiation as a function of the magnitude of the single-pass Faraday rotation and the parameters of the anisotropic cavity have been studied in a number of works [7-10], the approximations made in them limit the range of application of the results obtained. In particular, there are no published studies of the static characteristics of amplitude modulation with intraeavity magnetooptical control of the intensity of the output radiation of the laser with high gains in the active medium and both constant, introduced into the cavity by a real modulator, and controllable, arising under the action of the modulating radiation, significan t modulation losses. These conditions of internal modulation are present in a standard He-Ne laser when the Faraday effect in an yttrium-iron garnet single crystal Y~FesO12 is used to control the intensity of the output radiation at ~ = 3.39 ~m [5, 6].