Nonlinear Magneto-optics Research Articles

Giant and controllable nonlinear magneto-optical effects in two-dimensional magnets

The interplay of polarization and magnetism in materials with light can create rich nonlinear magneto-optical (NLMO) effects, and the recent discovery of two-dimensional (2D) van der Waals magnets provides remarkable control over NLMO effects due to their superb tunability. Here, based on first-principles calculations, we reported giant NLMO effects in CrI3-based 2D magnets, including a dramatic change of second-harmonics generation (SHG) polarization direction (90°) and intensity (on/off switch) under magnetization reversal and a 100% SHG circular dichroism effect. We further revealed that these effects could not only be used to design ultra-thin multifunctional optical devices but also to detect subtle magnetic orderings. Remarkably, we analytically derived conditions to achieve giant NLMO effects and proposed general strategies to realize them in 2D magnets. Our work not only uncovers a series of intriguing NLMO phenomena but also paves the way for both fundamental research and device applications of ultra-thin NLMO materials.

Stern-Gerlach deflection of vector spatio-temporal soliton pairs in cold Rydberg gases

We propose a scheme to investigate vector spatio-temporal soliton pairs via double Rydberg electromagnetically induced transparency (EIT). We show that three dimensional (3D) vector monopole and vortex solitons, with ultralow generation power and ultraslow speed, have been found under three response regions. In particular, these spatio-temporal soliton pairs experience a significant Stern-Gerlach deflection when a gradient magnetic field is applied to the system. The results reported here are useful not only for extending the research realm of nonlinear magneto-optics but also for the application in the detection of microgradient magnetic fields.

Giant Kerr nonlinearities and magneto-optical rotations in a Rydberg-atom gas via double electromagnetically induced transparency

We investigate the Kerr and magneto-optical effects for a probe laser field with two orthogonally polarized components, propagating in a cold Rydberg atomic gas with an inverted-Y-type level configuration via double electromagnetically induced transparency (EIT). Through an approach beyond both mean-field and ground-state approximations, we make detailed calculations on third-order nonlinear optical susceptibilities and show that the system possesses giant nonlocal selfand cross-Kerr nonlinearities contributed by Rydberg-Rydberg interaction. The theoretical result of the cross-Kerr nonlinearity obtained for 85Rb atomic gas is very close to the experimental one reported recently. Moreover, we demonstrate that the probe laser field can acquire a very large magnetooptical rotation via the double EIT, which may be used to design atomic magnetometers with high precision. The results presented here are promising not only for the development of nonlocal nonlinear magneto-optics but also for applications in precision measurement and optical information processing and transmission based on Rydberg atomic gases.

Stern-Gerlach deflection of optical Thirring solitons in a coherent atomic system

We propose a scheme to realize an optical Thirring model and create temporal optical Thirring solitons in a tripod-type atomic gas via double electromagnetically induced transparency (EIT). We show that giant enhancement of the cross-phase modulation for the two polarization components of the probe pulse can be obtained under the condition of the double EIT, and hence the optical Thirring model can be realized. We also show that the system supports stable temporal optical Thirring solitons, which have ultralow generation power and ultraslow propagation velocity. In particular, these temporal optical Thirring solitons may experience a significant Stern-Gerlach deflection when a gradient magnetic field is applied to the system. The results reported here are useful not only for extending the research realm of nonlinear magneto-optics but also for the application in precision measurements, such as the detection of microgradient magnetic fields.

Magneto-conductive encryption assisted by third-order nonlinear optical effects in carbon/metal nanohybrids

The influence of a magnetic field on electrical conductivity and the third-order nonlinear optical properties exhibited by carbon nanotubes decorated with platinum nanoparticles is reported. The experimental and numerical results of the nonlinear magneto-optics, magneto-conductivity and photo-thermal processes were analyzed. The simultaneous impact of optical absorptive nonlinearities and the magnetic field in the sample allowed us to encrypt information in the electronic signals by designing an exclusive-OR logic gate scheme. The samples were prepared in film form using a spray pyrolysis route and a chemical vapor deposition approach. The characterization of the morphological nature of the multiwall nanotubes was evaluated by transmission electron microscopy and x-ray techniques. A vectorial two-wave mixing method was conducted by using nanosecond pulses at 532 nm in order to estimate the nonlinear optical behavior in the nanohybrid materials explored. An important enhancement in the phonon-band-structured transport from the inclusion of nanoparticles in the nanotubes was numerically calculated. A distinguished modification in the transient dynamics of the photo-thermal transitions and Kerr nonlinearities was pointed out to be due to the metallic nanoparticles incorporated in the sample. An extraordinary evolution of the magneto-conductivity, together with a strong change in the optical Kerr transmittance exposed to the magnetic field in propagation through the nanostructures, was observed.

Ultrafast inhomogeneous magnetization dynamics analyzed by interface-sensitive nonlinear magneto-optics

We analyze laser-induced ultrafast, spatially inhomogeneous magnetization dynamics of epitaxial Co/Cu(001) films in a 0.4–10 nm thickness range with time-resolved magnetization-induced second harmonic generation, which probes femtosecond spin dynamics at the vacuum/Co and Co/Cu interfaces. The interference of these two contributions makes the overall signal particularly sensitive to differences in the transient magnetization redistribution between the two interfaces, i.e., ultrafast magnetization profiles in the ferromagnetic film. We conclude that the magnetization dynamics within the first several hundred femtoseconds is characteristically dependent on the Co film thickness. In films up to 3 nm thickness, we find a stronger demagnetization at the film surface compared to the Cu/Co interface, which we explain by a spin current from Co into the Cu substrate with an effective mean free path of about 3 nm. For film thicknesses larger than 3 nm, the transient magnetization profile over the Co film reverses its sign since spins can be transferred into the substrate only from the interface near region. Our work emphasizes that spatial inhomogeneities in the dynamic magnetic response to femtosecond laser excitation allow conclusions on the underlying microscopic processes.

Surface nonlinear optics and nonlinear magneto-optics at Moscow State University [Invited

In this paper, we present a brief review of the launch of surface nonlinear optics and nonlinear magneto-optics at Moscow State University in the 1980s and further development of these areas in Russia. The history of these branches of modern nonlinear optics cannot be separated from the history of Russia’s School of Nonlinear Optics founded by Rem V. Khokhlov and his colleagues and partners Sergey A. Akhmanov and David N. Klyshko. After a brief description of the basic contributions of the founding fathers, we present retrospection of surface nonlinear-optical and magneto-optical studies performed at the Physics Department of Moscow State University. In the last section, we present results of our recent studies of the relation between surface plasmons and magnetization-induced second-harmonic generation in magnetic nanoparticles.

Linear and nonlinear magneto-optics of ferritin

Measurements of Rayleigh light scattering and Cotton-Mouton (CM) effect are carried out at room temperature for 100 mM NaCl solutions of apoferritin/ferritin loaded with 0, 90, 100, 500, 700, and 1500 Fe atoms/molecule. Because of the spherical shape, ferritin macromolecule should not manifest magnetic anisotropy; however, in solution it shows the induced magnetic birefringence (CM effect) and changes in intensity of the scattered light components. The newly obtained data support the previously reported conclusions indicating that the deformation of linear optical polarizability induced in the ferritin by a magnetic field and the orientation of the induced magnetic dipole moment by this field are the main sources of the magneto-optical phenomena observed. Nevertheless, it is also found that the orientation of the permanent magnetic dipole moment contributes to both effects. The magnetic field induced changes in the light scattering and the CM effect theoretically depend on the linear magneto-optical polarizability, chi, on the nonlinear magneto-optical polarizability, eta, and square of the permanent magnetic dipole moment value of the macromolecule, mu(2). On the basis of the theory describing both effects as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizabilities components, the values of the linear optical polarizability and its anisotropy, nonlinear magneto-optical polarizability and its anisotropy, are estimated. Also the magnetic dipole moment of the ferritin macromolecule is found. Interestingly, not all iron atoms in the ferritin are indicated to be in the superparamagnetic state, some of them occur in the diamagnetic form.

Linear and nonlinear magnetooptics of planar Au/Co/Si nanostructures

Linear and nonlinear magnetooptics are applied to study the magnetic properties of Au/Co/Si planar nanostructures. The dependence of the nonlinear magneto-optical Kerr effect on the thickness of the cobalt layer, d Co, reaches a maximum at d Co ≈ 2 nm. This characteristic thickness is consistent with the formation of surface magnetization. An enhancement of the second harmonic generation (SHG) intensity and of magnetization-induced SHG is attained for an island-like structure of the cobalt layer, and is associated with the excitation of localized surface plasmons in cobalt nanoislands.

Nonlinear and Integrated Magneto-Optics

Nonlinear and Integrated Magneto-Optics

Dynamic effects in nonlinear magneto-optics of atoms and molecules: review

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Evgeniy B. Alexandrov, Marcis Auzinsh, Dmitry Budker, Derek F. Kimball, Simon M. Rochester, and Valeriy V. Yashchuk, "Dynamic effects in nonlinear magneto-optics of atoms and molecules: review," J. Opt. Soc. Am. B 22, 7-20 (2005) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Relation between electromagnetically induced absorption resonances and nonlinear magneto-optics inΛsystems

Recent work on Lambda-resonances in alkali metal vapors (E. Mikhailov, I. Novikova, Yu. V. Rostovtsev, and G. R. Welch, quant-ph/0309171, and references therein) investigated a type of electromagnetically induced absorption resonance that occurs in three-level systems under specific conditions normally associated with electromagnetically induced transparency. In this note, we show that these resonances have a direct analog in nonlinear magneto-optics, and support this conclusion with a calculation for a J=1->J'=0 system interacting with a single nearly circularly polarized light field in the presence of a weak longitudinal magnetic field.

Resonant nonlinear magneto-optical effects in atoms

The authors review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. They begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances. These effects are then contrasted with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultranarrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms.

Effective-medium theory for nonlinear magneto-optics in magnetic granular alloys: cubic nonlinearity

We propose a simple effective-medium approach for calculating the effective dielectric function of a magnetic metal–insulator granular alloy in which there is a weakly nonlinear relation between electric displacement D and electric field E for both constituent materials of the form D i=ε i (0) E i +χ i (3)| E i| 2 E i . We assume that linear ε i (0) and cubic nonlinear χ i (3) dielectric functions are diagonal and linear with magnetization non-diagonal components. For such metal–insulator composite magneto-optical effects depend on a light intensity and the effective cubic dielectric function χ eff (3) can be significantly greater (up to 10 3 times) than that for constituent materials. The calculation scheme is based on the Bergman and Stroud-Hui theory of nonlinear optical properties of granular matter. The giant cubic magneto-optical nonlinearity is found for composites with metallic volume fraction close to the percolation threshold and at a resonance of optical conductivity. It is shown that a composite may exhibit nonlinear magneto-optics even when both constituent materials have no cubic magneto-optical nonlinearity.

Detection of coherent and incoherent spin dynamics during the magnetic switching process using vector-resolved nonlinear magneto-optics

It is usually assumed that magnetic switching proceeds via coherent rotation under conditions of high symmetry. There is no a priori reason to expect an inhomogeneous response when a uniform magnetic torque is applied to a homogeneous ferromagnet. We test this assumption using vector- and time-resolved nonlinear magneto-optic measurements on a continuous Ni–Fe film. While coherent dynamics are observed when the magnetization M is initially oriented along the easy axis (the preferred axis of M in the absence of external fields), we find evidence for inhomogeneous spin dynamics when M is initially oriented perpendicular to the easy axis, which suggests the generation of incoherent spin waves during the magnetic reorientation process. The inhomogeneity is sufficient to reduce the spatially averaged magnetic moment within the measured area by almost 50%.

Phase transitions of MnO3 compounds revealed by nonlinear magnetooptics

Magnetic second-harmonic generation (SHG) and three-photon difference-frequency generation (DFG) are used to investigate the magnetic phase diagrams of MnO3 3- compounds with five- and sixfold coordination of the Mn3+ (3d4) ion. In the hexagonal manganites, the six basic antiferromagnetic structures following from a one-dimensional representational analysis of the hexagonal unit cell are clearly distinguished on the basis of their different selection rules for SHG. All structures break the geometric frustration of the unit cell by triangular antiferromagnetic ordering of the Mn spins. The stability and the mutual interactions of in-plane and inter-plane exchange and the in-plane anisotropy are investigated. The three quantities act as almost decoupled degrees of freedom, which leads to independent in-plane and inter-plane reorientations of the Mn spin lattice. DFG was observed in the orthorhombic manganites Pr1-xCaxMnO3 and Nd1-xSrxMnO3. The DFG reflects the fourfold anisotropy of the quasicubic crystal, and the independent tensor elements for DFG are determined quantitatively. A metal–insulator transition with a two-order-parameter coupling to antiferromagnetism and charge ordering leads to additional difference-frequency contributions, which allow us to observe the formation of ∼100 μm magnetic domains. The variety of results gained from the two vastly different groups of manganite compounds, with spectral and spatial resolution used as additional degrees of freedom, demonstrates the versatility of nonlinear magnetooptical experiments for the investigation of magnetic structures and symmetries.

Non-linear optics and magneto-optics on nano-structured interfaces

The behaviour of the reflectivity and Kerr magneto-optic effects in the non-linear second-harmonic (SH) field diffracted from nano-scale structured ferromagnetic interfaces is reported. Measurements are made in both the linear and non-linear fields at two different fundamental wavelengths (1064 nm and 800 nm) and their associated harmonics. Resonant behaviour observed as a function of angle of incidence is identified with surface-plasmon production that is known to intensify the local field within the interface. Radiation incident at angles of incidence that optimise coupling to the electron plasma produces an increase in the SH field radiated in the vicinity of those angles. Similarly, at those angles of incidence where radiation at the SH wavelengths (532 nm and 400 nm) couples optimally to the electron plasma, troughs are seen in the angular spectrum of the generated SH radiation. Kerr magneto-optic measurements taken in both the linear field and the SH field both show very significant enhancement at angles meeting the plasma-resonance condition. The totality of experimental data presented allows the conclusion that intensification of the interface electric field due to plasmon creation enhances not only the SH reflection coefficient, as was already known, but also the magneto-optic reflection coefficients in both linear and SH fields.

Magnetic second harmonic study of Cr/Fe and Ag/Fe buried interfaces

The magnetic properties of Ag/Fe/MgO and Cr/Fe/MgO multilayers have been studied in air by both linear (MOKE) and non-linear (MSHG) magneto-optics. Thanks to the different probing sensitivities of the two techniques, film and interface properties can be separately measured. In the Ag/Fe/MgO case, coercive field values measured with linear and non-linear optics are very similar, indicating that a sharp interface is formed and that the presence of silver on top of iron does not alter its magnetic properties. The values of coercive field measured with MOKE for the Cr/Fe/MgO multilayer differ significantly with respect to the Ag case, and furthermore different coercive fields have been measured on this system with MOKE and MSHG. We ascribe the observed effects to spin frustration caused the layered antiferromagnetic Cr spin structure along with the presence of steps at the Cr/Fe interface.

Nonlinear magneto-optics in magnetic nanoparticles

In this paper, the results of our recent studies of the magnetization-induced nonlinear optical effects in magnetic nanoparticles are surveyed. There are three aspects of nonlinear magneto-optics of nanoparticles, which attract attention in this review being interdisciplinary in terms of magnetism, low-dimensionality, nonlinear and coherent optics. The first is the fact that the nonlinear magneto-optical Kerr effect (NOMOKE), i.e. magnetization-induced second-harmonic generation (MSHG), exists in magnetic nanogranular films simultaneously with giant magnetoresistance effect (GMR). Moreover, the NOMOKE contrast attains maximum at the same content of magnetic component in magnetic nanogranular films as the maximum of GMR coefficient. Up to now nonlinear magneto-optics was concentrated on the regular magnetic systems and as a consequence described a coherent nonlinear response. On the contrary, in recent studies an attention is turned to the random magnetic nanostructures and, in particular, to the random two-dimensional arrays of magnetic nanoparticles fabricated by Self-Assembly techniques. Thus, an incoherent analog of MSHG, which can be called: magnetization-induced hyper-Rayleigh scattering, is observed. And finally a general issue of intrinsic weakness of magnetization-induced nonlinear optical effects governed by the fine structure parameter is discussed in terms of internal homodyne effect as one of the mechanisms of an enhancement of the magnetic effects in nonlinear optics.

Nonlinear magneto-optical properties of colossal magnetoresistive manganites.

Pr(1--x)CaxMnO(3) and Nd(1--x)SrxMnO(3) were investigated with three-photon difference frequency generation (DFG). This method allows one to determine both the crystalline and the magnetic symmetry. In the highly ordered low-temperature phase of Nd(0.50)Sr(0.50)MnO(3), a DFG contribution coupling simultaneously to antiferromagnetic and charge ordering was observed and used to reveal the formation of domains. Thus, magnetically induced three-photon processes are introduced into the fields of both nonlinear magneto-optics and colossal magnetoresistance as a powerful new method.