Magneto-optical Configuration Research Articles

Atom-based optical polarization modulator.

In this work, we employ 87Rb atoms as rotation media to manipulate the polarization of optical fields in both magnetic and magnetic-free environments. Employing the nonlinear magneto-optical rotation mechanism, we achieve a state-of-the-art magneto-optical rotation coefficient of 1.74×108 rad⋅T-1⋅m-1 which is four orders of magnitude higher than commonly employed materials. Additionally, in a magnetic-free environment, we achieve all-optical cross-polarization modulation between the pump and probe light via Rb atoms. The nonlinear magneto-optical rotation configuration introduces inventive techniques for a new type of magneto-optical modulator while the all-optical configuration paves the way for exploring photonic integrated circuit (PIC) devices free from disruptions caused by electrical or magnetic crosstalk.

Trace of evanescent wave polarization by atomic vapor spectroscopy

Various efforts have been made to determine the polarization state of evanescent waves in different structures. The present study shows the reliability of magneto-optical spectroscopy of D1 and D2 lines of rubidium metal and polarization-dependent transitions to investigate and trace the changes in the polarization state of evanescent fields during total internal reflection over different angles. For this purpose, we design and fabricate atomic- evanescent Rb vapor cells and examine the effect of polarization changes of evanescent waves, depending on the propagation direction of evanescent waves in anisotropic rubidium vapor media under 88 mT external magnetic field by different configurations theoretically and experimentally. The results confirm the dependency of allowed sigma^{ pm } { };{text{and}};pi transitions on the magneto optical configuration as a tool to determine changes in the polarization of evanescent waves in more complicated wave states in anisotropic media.

A Compact Laser Pumped 4He Magnetometer with Laser-Frequency Stabilization by Inhomogeneous Light Shifts

We propose a compact 4He magnetometer realizing magnetic field measurement and laser-frequency stabilization simultaneously in a single 4He atomic cell. The frequency stabilization scheme is based on the asymmetric line shape of magnetic resonance which is induced by spatially inhomogeneous light shifts. We investigate the asymmetric line shape of the magnetic resonance signal theoretically and experimentally in laser pumped 4He magnetometer with the magneto-optical double-resonance configuration. Notice that, due to the asymmetric line shape, the in-phase component of the magnetic resonance signal is shown to have a linear dependence with respect to the laser frequency detuning and is used to actively lock the laser frequency to the resonant point. The method reduces the complexity of the system and improves the stability of the magnetometer, making the laser-pumped 4He magnetometer more compact and portable.

Ultrahigh-quality electromagnetically induced absorption resonances in a cesium vapor cell

Electromagnetically induced absorption (EIA) of cesium atoms exposed to counter-propagating light waves with orthogonal linear polarizations is studied. Probe beam transmission through a buffer gas-filled vapor cell is monitored as a function of a static magnetic field applied parallel to the wave vectors. The light waves are tuned to a single dipole transition Fg → Fe in the D1 line (λ = 894.6 nm). The proposed magneto-optical configuration helps overcome a long-standing problem in obtaining high-contrast EIA resonances in conjunction with narrow linewidths. Our experiments demonstrate EIA contrast with respect to a broad Doppler absorption background (CD) as high as 1630%. Thus, a high value of CD means that background absorption is almost absent, and the vapor cell transmission profile represents only a single narrow resonance. This result is unique for EIA as well as for electromagnetically induced transparency (EIT) effects, because usually in a resonant medium, narrow EIT or EIA resonances are accompanied by natural-linewidth or other broad spectral features, even in the case of cold atoms. The resonance contrast with respect to the light transmission background (Cback) is also high enough, reaching 75% in the experiments. The full width at half maximum of the narrowest observed EIA is approximately 0.77 mG (0.7 × 0.77 = 540 Hz in the frequency domain). The considered simple scheme has good prospects for the development of various quantum magneto-optical devices such as optical switches and atomic magnetometers.

Characteristics of unconventional Rb magneto-optical traps

We study several new magneto-optical trapping configurations in $^{87}$Rb. These unconventional MOTs all use type-II transitions, where the angular momentum of the ground state is greater than or equal to that of the excited state, and they may use either red-detuned or blue-detuned light. We describe the conditions under which each new MOT forms. The various MOTs exhibit an enormous range of lifetimes, temperatures and density distributions. At the detunings where they are maximized, the lifetimes of the various MOTs vary from 0.1 to 15 s. One MOT forms large ring-like structures with no density at the centre. The temperature in the red-detuned MOTs can be three orders of magnitude higher than in the blue-detuned MOTs. We present measurements of the capture velocity of a blue-detuned MOT, and we study how the loss rate due to ultracold collisions depends on laser intensity and detuning.

Supermodes in Coupled Bigyrotropic Slab Waveguides

We consider a system of two coupled magneto-optical single-mode slab waveguides separated by an isotropic dielectric spacer. In the transverse magneto-optical configuration, the TE/TM states of polarization can be handled separately. The even/odd supermodes are derived in much the same way as in similar non-magnetic coupled systems; perfect phase-matching ensures a total transfer of energy from one waveguide to the other. The coupling constant can be related to the difference between the propagation constants of the even (slow) and odd (fast) supermodes. Besides, while reversing the magnetization in one of the two waveguides does not affect the phase-matching, it does change the coupling mechanism in a subtle way, thus allowing a magnetic control of the supermodes and of the polarization-dependent coupling efficiency.

Nonreciprocal waveguiding structures for THz region based on InSb.

We have studied theoretically and numerically surface magnetoplasmons in three types of THz guiding structures, namely, InSb/dielectric planar boundary, InSb/air/metal planar waveguide, and symmetric InSb/air/InSb planar waveguide, in the presence of an external magnetic field. We consider the Voigt magneto-optic configuration in which these structures provide a frequency range where only one propagation direction is allowed to support one-way propagation of the surface plasmon polariton, due to nonreciprocity of the structures. To study the dispersion properties associated with unidirectional propagation of magnetoplasmons in finite-size nanostructured waveguides, we have developed an efficient two-dimensional numerical technique based on the magneto-optic aperiodic rigorous coupled-wave analysis. We have shown that the one-way bandwidth can be controlled by an external magnetic field and by the permittivity and thickness of the dielectric guiding layer. To enable numerical simulation, we have utilized the configuration in which the magnetized section of a waveguide is along the direction of propagation sandwiched by the identical waveguide segments without a magnetic field. We have also shown that the one-way bandwidth can be controlled by an external magnetic field and by the permittivity and thickness of the dielectric guiding layer.

Relationships between the magnetic structure parity of an easy-axis antiferromagnet and the refraction mode of electromagnetic waves of the TM and TE types

The role of antisymmetry in the refraction processes of electromagnetic waves of the TM and TE type that recede from nonmagnetic media at an arbitrary angle on the surface of a compensated antiferromagnet for a longitudinal magnetooptical configuration is examined.

High Transmission Enhanced Faraday Rotation in Coupled Resonator Magneto-Optical Waveguides

We propose a novel magneto-optical waveguide configuration consisting of coupled-resonator magneto-optical waveguides to obtain enhanced transmission and Faraday rotation. We show theoretically that such a configuration can enhanced the localization of light and as a result, enhanced Faraday rotation and transmittance simultaneously. The calculations revealed that required optical isolator performance, transmittance 95%, Faraday rotation angle 22.81 degree and large amount of magneto-optical figure of merit, can be fulfilled with our optimized waveguide. Since our investigation showed that the use of optimized one dimensional coupled resonator magneto-optical waveguide with a rotation of half of 45 degree would make it possible to assemble low loss magneto-optical isolators.

Dispersion of bulk and surface electromagnetic waves in bigyrotropic finely stratified ferrite-semiconductor medium

Expressions for effective parameters are derived for a medium composed of alternating layers of a uniaxial ferromagnet and a semiconductor. The medium under investigation is a biaxial bigyrotropic crystal. In the case of a transverse magnetooptical configuration, bulk and surface waves at the vacuum-periodic structure interface are considered. Numerical analysis of dispersion relations for intrinsic TE and TM modes controlled in different frequency ranges is carried out.

Modeling of magneto-optical properties of lamellar nanogratings

Optical and magneto-optical (MO) properties of the MO nanometer-size gratings (nanogratings) are modeled using improved rigorous couple wave analysis (RCWA). The improvements include S-matrix propagation algorithm and Fourier factorization rules and lead to necessary numerical precision for the modeled quantities. The rigorous model is compared with effective medium approximation (EMA), used for simple description of the grating parameters, and the areas of differences are discussed. Dependence of optical and MO elements of permittivity tensor on the fill factor is presented together with comparison to the EMA. Basic polar, longitudinal, and transverse MO configuration are studied.

Spectra of bigyrotropic magnetic photonic crystals

We calculated the photonic band gap spectra of a one-dimensional magnetic photonic crystal made of alternating layers of bigyrotropic magnetic yttrium-iron garnet and nonmagnetic gadolinium gallium garnet. The forbidden regimes or band gaps in the electromagnetic wave spectrum were numerically obtained for the transversal magneto-optical configuration and compared with those for the polar and longitudinal magneto-optical configurations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

First-Principles Calculation of Nonlinear Surface Magneto-Optical Response of a Ferromagnetic Multilayer

First-principles calculations, based on the full-potential linearized augmented plane wave (FLAPW) method, including spin-orbit coupling (SOC) as second variational treatment within a self-consistent procedure, were carried out to obtain the nonlinear optical (NLO) response from the fcc multilayer structure [Ni(1 ML)/Cu(1 ML)]2, grown on Cu(001). Within the framework of a supercell approach we obtain the wave unctions and the bandstructure for further calculation of the spectra of the nonlinear optical susceptibility tensor χijk(2). The reflected electric field at the frequency of the second harmonic (SHG) 2ω is calculated on the basis of the surface-sheet model and the resulting SHG intensities, azimuthal dependence for main experimental geometries and Kerr angles are presented for the cases of the in-plane and out-of-plane magnetization of the multilayer, which correspond to longitudinal and polar magneto-optical configurations (MOC) respectively. We compare current results with previously obtained ones for the single fcc Ni/Cu(001) bilayer. It is shown, that in the case of the out-of-plane magnetization the magnetic tensor elements of the χijk(2) tensor are smaller than the nonmagnetic ones by only one order of magnitude. In the case of in-plane magnetization the magnetically induced components of χijk(2) become even comparable in magnitude with the nonmagnetic ones, confirming the important role of magnetic properties in the NLO response.

Nonlinear surface magneto-optics of ferromagnetic Ni/Cu(001) from first principles

We present first-principles calculations of the nonlinear optical (NLO) response of a Ni/Cu(001) bilayer. The calculations are based on the full potential linearized augmented plane wave (FLAPW) method with the additional implementation of spin–orbit coupling (SOC). On the basis of this set of eigenstates the magneto-optical transition-matrix elements are evaluated. Using the surface-sheet model the optical reflection properties are determined for the cases of the magnetization vector perpendicular to the surface (polar magneto-optical configuration (MOC)) and for the in-plane magnetization (longitudinal MOC). The nonlinear optical susceptibility tensor elements χ(2) ijk for different magnetization directions as well as the spectral dependence of χ(2) ijk, the resulting intensities, and Kerr angles are presented for the Ni/Cu(001) bilayer. The results show that the magnetic tensor elements of the χ(2) ijk tensor are smaller than the nonmagnetic ones by only one order of magnitude, confirming the important role of magnetic properties in the NLO response.

Integrated magnetooptic cross strip isolator

A bimodal planar waveguide segment of specific length and thickness between two thinner single mode sections can serve as an interferometer. Depending on the phase gain of the two modes in the thick region, these fields can interfere destructively or constructively at the transition from the bimodal to the single mode section. We employ this geometry to realize a simple magnetooptic isolator configuration, using a wide strip that is etched into a double layer in-plane magnetized magnetooptic film. The magnetization is oriented parallel to the strip; the light traverses the strip perpendicularly. Then the magnetooptic effect causes the phase velocities of TM polarized waves to be different for opposite directions of light propagation, resulting in a nonreciprocal power transfer across the strip. For a properly selected geometry one can expect isolator performance. If the strip width varies slightly, then adjusting the beam incoupling position means to change the distance which the light travels in the two mode segment. This offers a convenient tuning possibility, which may be a means to overcome the strict fabrication tolerances that apply usually to interferometric integrated isolator concepts.

Wide aperture kinematic separator COMBAS realized on the strong focusing principle

The COMBAS large solid angle and high momentum acceptance and high-resolving kinematic separator has been created at the Flerov Laboratory of Nuclear Reactions, JINR, to efficiently collect extremely short-lived nuclei near the zero angle which are produced in intermediate energy fragmentation reactions with wide momentum and wide angular distributions. For the first time the M 1M 2M 3M 4F dM 5M 6M 7M 8F a magneto-optical configuration of the COMBAS separator has been realized on the strong focussing principle. The separation and trajectory analysis of particles by the separator are carried out by three parameters: the magnetic rigidity (B· ρ), the energy loss difference in the degrader (Δ E/Δ x) and the time-of-flight (Δ T) of the analyzed particles. The COMBAS separator can be used efficiently both in the mode of a high- resolving spectrometer to study reaction mechanisms and in the mode of an in-flight separator in experiments on the synthesis and study of properties of short-lived exotic nuclei near the drip-lines.

Noncollinear coplanar magneto-optic interaction of guided optical wave and magnetostatic surface waves in yttrium iron garnet-gadolinium gallium garnet waveguides

Wideband noncollinear coplanar guided-wave magneto-optic diffraction and mode conversion by magnetostatic surface waves at multigigahertz (3–7 GHz) carrier frequencies in yttrium iron garnet-gadolinium gallium garnet waveguides have been observed and measured in detail for the first time. Interaction configuration, physical mechanisms, summary of a theoretical treatment, and some experimental results obtained at 1.152 μm optical wavelength are presented. This noncollinear coplanar magneto-optic interaction configuration should result in a number of integrated optic devices for wideband communications and signal processing applications at electronically tunable microwave carrier frequencies. The potential advantages of the resulting magneto-optic devices over the existing acousto-optic devices are also discussed.

New Methods of Magneto-optical Signal Modulation and Detection

Methods of modulating magneto-optical signals are useful in improving the signal-to-noise ratio of practical systems. Using the longitudinal or polar magneto-optical orientation and incident light polarized out of the plane of incidence (say at 45°), an intensity-modulated magneto-optical signal can be generated by modulating the phase of the component of light which is ‖ (or ⊥) to the plane of incidence. No analyzer is required with the consequence that this type of modulation can be used in fully focused light if axial symmetry is maintained. Signal modulation can also be obtained by thermal modulation of the magnetic material. For a 1-μ-diam region of a thin film the frequency response is calculated to be ∼500 MHz. Various magneto-optical configurations are readily devised which yield the value of a bit (1 or 0) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. If the thermal modulation is effected by an electron beam, the need for a high-resolution optical deflector is eliminated in a high-bit-density computer-memory application.

Proposal for a magnetic-film memory accessed by combined photon and electron beams

A magnetic-film memory accessed by combined photon and electron beams is proposed. The electron beam is used to heat a selected bit, which results in lowering the switching threshold so that information can be written selectively into that bit by means of an external magnetic field. Reading is accomplished by simultaneously illuminating a bit with an electron and a photon beam. Then a thermally modulated magnetic-optical signal is generated by intensity modulation of the electron beam. This arrangement is advantageous since a high-resolution photon beam and photon deflector are not required. The frequency response for thermally modulating a 1-μm bit is calculated to be ∼500 MHz; the necessary temperature dependence of the magneto-optical coefficient and the coercive force can be obtained by using composite films made from layers having different Curie points. Various magneto-optical configurations are readily devised which yield the value of a bit (one or zero) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. The shot noise limited signal-to-noise ratio (SNR) is determined by heating of a bit from the photon beam. It is calculated that for a low-loss magnetooptical material such as EuO a 1-μm bit can be read in 1 μs when illuminated with a 1000-μm photon beam. The base-line temperature rise due to heating from the photon beam can be kept small by using narrow pulses of light (width \sim10^{-11} second), as, for example, from a mode-locked laser.