Cotton-Mouton Effect Research Articles

Megagauss magnetic fields in ultra-intense laser generated dense plasmas

Table-top terawatt lasers can create relativistic light intensities and launch megaampere electron pulses in a solid. These pulses induce megagauss (MG) magnetic pulses, which in turn strongly affect the hot electron transport via electromagnetic instabilities. It is therefore crucial to characterize the MG magnetic fields in great detail. Here, we present measurements of the spatio-temporal evolution of MG magnetic fields produced by a high contrast (picosecond intensity contrast 10−9) laser in a dense plasma on a solid target. The MG magnetic field is measured using the magneto-optic Cotton–Mouton effect, with a time delayed second harmonic (400 nm) probe. The magnetic pulse created by the high contrast laser in a glass target peaks much faster and has a more rapid fall than that induced by a low contrast (10−6) laser.

Theoretical and numerical evaluation of polarimeter using counter-circularly-polarized-probing-laser under the coupling between Faraday and Cotton-Mouton effect.

This study evaluated an effect of an coupling between the Faraday and Cotton-Mouton effect to a measurement signal of the Dodel-Kunz method which uses counter-circular-polarized probing-laser for measuring the Faraday effect. When the coupling is small (the Faraday effect is dominant and the characteristic eigenmodes are approximately circularly polarized), the measurement signal can be algebraically expressed and it is shown that the finite effect of the coupling is still significant. When the Faraday effect is not dominant, a numerical calculation is necessary. The numerical calculation under an ITER-like condition (Bt = 5.3 T, Ip = 15 MA, a = 2 m, ne = 10(20) m(-3) and λ = 119 μm) showed that difference between the pure Faraday rotation and the measurement signal of the Dodel-Kunz method was an order of one degree, which exceeds allowable error of ITER poloidal polarimeter. In conclusion, similar to other polarimeter techniques, the Dodel-Kunz method is not free from the coupling between the Faraday and Cotton-Mouton effect.

Design of a collective scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research.

The design characteristics of a multi-channel collective (or coherent) scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research (KSTAR), which is planned to be installed in 2017, are given in this paper. A few critical issues are discussed in depth such as the Faraday and Cotton-Mouton effects on the beam polarization, radial spatial resolution, probe beam frequency, polarization, and power. A proper and feasible optics with the 300 GHz probe beam, which was designed based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wavenumbers up to 24 cm(-1). The upper limit corresponds to the normalized wavenumber kθρe of ∼0.15 in nominal KSTAR plasmas. To detect the scattered beam power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed.

Magneto-optical switching devices based on Si resonators

The magneto-optical switching devices based on Si ring and Si photonic crystal resonators have been fabricated using a Bi3Fe5O12 (BIG) film deposited by the metal organic decomposition (MOD) method. The quality of the obtained BIG film was evaluated by X-ray diffraction and the magneto-optical Kerr effect and relatively good results were obtained. The light modulations of both devices were ≦20% at a wavelength of ∼1.5 µm. The operation mechanisms of both devices are explained by the Cotton–Mouton effect where the magnetic field direction is perpendicular to the light propagation direction.

Pulsed field probe of real time magnetization dynamics in magnetic nanoparticle systems

Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field “snapshot” is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

Circular and linear magnetic birefringences in xenon at λ = 1064 nm.

The circular and linear magnetic birefringences corresponding to the Faraday and the Cotton-Mouton effects, respectively, have been measured in xenon at λ = 1064 nm. The experimental setup is based on time dependent magnetic fields and a high finesse Fabry-Pérot cavity. Our value of the Faraday effect is the first measurement at this wavelength. It is compared to theoretical predictions. Our uncertainty of a few percent yields an agreement at better than 1σ with the computational estimate when relativistic effects are taken into account. Concerning the Cotton-Mouton effect, our measurement, the second ever published at λ = 1064 nm, agrees at better than 1σ with theoretical predictions. We also compare our error budget with that established for other experimental published values.

Inside Cover: Nuclear‐Spin‐Induced Cotton–Mouton Effect in a Strong External Magnetic Field (ChemPhysChem 11/2014)

Inside Cover: Nuclear‐Spin‐Induced Cotton–Mouton Effect in a Strong External Magnetic Field (ChemPhysChem 11/2014)

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed for excitation fluences higher than 100 mJ/cm2.

Dissimilar permittivity and permeability sensitivities in nonlinear plasmons and spoof plasmons.

We show that employing localized surface plasmon resonators to probe environmental media will always lead to dissimilar optical sensitivities to permittivity and permeability. We find that while the permittivity sensitivities of diverse plasmonic structures display a geometry-independent universal scaling relation, the permeability sensitivities are highly dependent on the metals' geometries and resonant modes. Similar results are also found in mixed real/spoof localized surface plasmon resonators, and the phenomena can be universally scaled to the normalized effective plasmon frequencies. Importantly, the results put a fundamental constraint for all plasmonic-assisted nonlinear magneto-optical phenomena, including the Faraday effect, magneto-optical Kerr effect, and Cotton-Mouton effect.

Magnetic instability in AdS/CFT: Schwinger effect and Euler-Heisenberg Lagrangian of supersymmetric QCD

To reveal the Schwinger effect for quarks, i.e., pair creation process of quarks and antiquarks, we derive the vacuum decay rate at strong coupling using AdS/CFT correspondence. Magnetic fields, in addition to the electric field responsible for the pair creation, causes prominent effects on the rate, and is important also in experiments such as RHIC/LHC heavy ion collisions. In this paper, through the gravity dual we obtain the full Euler-Heisenberg Lagrangian of N=2 supersymmetric QCD and study the Schwinger mechanism with not only a constant electric field but also a constant magnetic field as external fields. We determine the quark mass and temperature dependence of the Lagrangian. In sharp contrast with the zero magnetic field case, we find that the imaginary part, and thus the vacuum decay rate, diverges in the massless zero-temperature limit. This may be related to a strong instability of the QCD vacuum in strong magnetic fields. The real part of the Lagrangian serves as a generating function for non-linear electro-magnetic responses, and is found such that the Cotton-Mouton effect vanishes. Interestingly, our results of the Schwinger / Cotton-Mouton effects coincide precisely with those of N=2 supersymmetric QED.

Nuclear-spin-induced cotton-mouton effect in a strong external magnetic field.

Novel, high-sensitivity and high-resolution spectroscopic methods can provide site-specific nuclear information by exploiting nuclear magneto-optic properties. We present a first-principles electronic structure formulation of the recently proposed nuclear-spin-induced Cotton-Mouton effect in a strong external magnetic field (NSCM-B). In NSCM-B, ellipticity is induced in a linearly polarized light beam, which can be attributed to both the dependence of the symmetric dynamic polarizability on the external magnetic field and the nuclear magnetic moment, as well as the temperature-dependent partial alignment of the molecules due to the magnetic fields. Quantum-chemical calculations of NSCM-B were conducted for a series of molecular liquids. The overall order of magnitude of the induced ellipticities is predicted to be 10(-11) -10(-6) rad T(-1) M(-1) cm(-1) for fully spin-polarized nuclei. In particular, liquid-state heavy-atom systems should be promising for experiments in the Voigt setup.

Magneto-Elastic Effects in Tb3Ga5O12

We report new results for the elastic constants studied in Faraday and Cotton–Mouton geometry in Tb3Ga5O12 (TGG), a frustrated magnetic substance with strong spin–phonon interaction and remarkable crystal-electric-field (CEF) effects. We analyze the data in the framework of CEF theory taking into account the individual surroundings of the six inequivalent Tb3+-ion positions. This theory describes both, elastic constants in the magnetic field and as a function of temperature. Moreover we present sound-attenuation data for the acoustic Cotton–Mouton effect in TGG.

Spin dynamics of antiferromagnets under action of femtosecond laser pulses (Review Article)

Investigations of excitation of spin dynamics in transparent antiferromagnets (AFM) under the action of femtosecond laser pulses are reviewed. A variety of observed effects is considered in the context of a unified approach. The analysis is based on the nonlinear sigma model for the antiferromagnetism vector L with taking into account effective fields induced in a magnetic material due to the interaction between light and the spin system of the magnetic material. The contributions of various magneto-optical effects (both standard Faraday or Cotton-Mouton (Voigt) effects and specific L-dependent effects for AFM) are considered as characteristic contributions to the effective field within the sigma model. The most typical experimental data for real AFM are discussed.

Nuclear quadrupole moment-induced Cotton-Mouton effect in molecules

Nuclear magneto-optic effects could make important contributions to novel, high-sensitivity, and high-resolution spectroscopic and imaging methods that provide nuclear site-specific structural and dynamic information on molecular and materials systems. Here we present a first-principles electronic structure formulation of nuclear quadrupole moment-induced Cotton-Mouton effect in terms of response theory, as well as ab initio and density-functional theory calculations of this phenomenon for a series of molecular liquids: H2O, CH3NO2, CH3CH2OH, C6H6, C6H12 (cyclohexane), HI, XeF2, WF5Cl, and Pt(C2dtp)2. The roles of basis-set convergence, electron correlation, and relativistic effects are discussed. The estimated order of magnitude of the overall ellipticities induced to linearly polarized light is 10(-3)-10(-7) rad/(M cm) for fully spin polarized nuclei. The cases with the largest presently obtained ellipticities should be detectable with modern instrumentation in the Voigt magneto-optic setup, particularly for the heavy nuclei.

Polarization tomography of the tokamak plasma magnetic field

Optical polarization tomography of the tokamak plasma magnetic field is considered in the context accepted for large magnetic fields. Two models of the interaction between the magnetic field and radiation are studied: (1) the Faraday rotation (FR) of the polarization plane is imposed on birefringence caused by the toroidal component and (2) the Cotton-Mouton effect (CME) is imposed on the FR. Previously, these problems were solved with allowance for only one of the optical effects. New integrals caused by the amplification of the magnetic field are added to ray integrals used earlier. The retrieval of the magnetic field is based on the vector Radon transform (VRT) of imaginary absorption. Formulas of the inverse VRT are derived using generalized conditions from R. Novikov on the Radon transform with absorption.

High-resolution measurements of the spatial and temporal evolution of megagauss magnetic fields created in intense short-pulse laser-plasma interactions

A pump-probe polarimetric technique is demonstrated, which provides a complete, temporally and spatially resolved mapping of the megagauss magnetic fields generated in intense short-pulse laser-plasma interactions. A normally incident time-delayed probe pulse reflected from its critical surface undergoes a change in its ellipticity according to the magneto-optic Cotton-Mouton effect due to the azimuthal nature of the ambient self-generated megagauss magnetic fields. The temporal resolution of the magnetic field mapping is typically of the order of the pulsewidth, limited by the laser intensity contrast, whereas a spatial resolution of a few μm is achieved by this optical technique. High-harmonics of the probe can be employed to penetrate deeper into the plasma to even near-solid densities. The spatial and temporal evolution of the megagauss magnetic fields at the target front as well as at the target rear are presented. The μm-scale resolution of the magnetic field mapping provides valuable information on the filamentary instabilities at the target front, whereas probing the target rear mirrors the highly complex fast electron transport in intense laser-plasma interactions.

Measurement of the Cotton Mouton effect of water vapour

In this Letter we report on a measurement of the Cotton Mouton effect of water vapour. Measurements performed at room temperature (T=301K) with a wavelength of 1064nm gave the value Δnu=(6.67±0.21)·10-15 for the magnetic birefringence at 1T magnetic field and atmospheric pressure.

Biaxiality-induced magnetic field effects in bent-core nematics: Molecular-field and Landau theory

Nematic liquid crystals composed of bent-core molecules exhibit unusual properties, including an enhanced Cotton-Mouton effect and an increasing isotropic (paranematic)-nematic phase transition temperature as a function of magnetic field. These systems are thought to be good candidate biaxial liquid crystals. Prompted by these experiments, we investigate theoretically the effect of molecular biaxiality on magnetic-field-induced phenomena for nematic liquid crystals, using both molecular field and Landau theory. The geometric mean approximation is used in order to specify the degree of molecular biaxiality using a single parameter. We reproduce experimental field-induced phenomena and predict also an experimentally accessible magnetic critical point. The Cotton-Mouton effect and temperature dependence of the paranematic-nematic phase transition are more pronounced with increased molecular biaxiality. We compare our theoretical approaches and make contact with recent relevant experimental results on bent-core molecular systems.

Communication: Nuclear quadrupole moment-induced Cotton-Mouton effect in noble gas atoms

New, high-sensitivity and high-resolution spectroscopic and imaging methods may be developed by exploiting nuclear magneto-optic effects. A first-principles electronic structure formulation of nuclear electric quadrupole moment-induced Cotton-Mouton effect (NQCME) is presented for closed-shell atoms. In NQCME, aligned quadrupole moments alter the index of refraction of the medium along with and perpendicular to the direction of nuclear alignment. The roles of basis-set convergence, electron correlation, and relativistic effects are investigated for three quadrupolar noble gas isotopes: (21)Ne, (83)Kr, and (131)Xe. The magnitude of the resulting ellipticities is predicted to be 10(-4)-10(-6) rad/(M cm) for fully spin-polarized nuclei. These should be detectable in the Voigt setup. Particularly interesting is the case of (131)Xe, in which a high degree of spin polarization can be achieved via spin-exchange optical hyperpolarization.

Faraday and Cotton-Mouton effects of helium atλ=1064nm

We present measurements of the Faraday and the Cotton-Mouton effects of helium gas at $\lambda =~1064$\,nm. Our apparatus is based on an up-to-date resonant optical cavity coupled to longitudinal and transverse magnetic fields. This cavity increases the signal to be measured by more than a factor of 270\,000 compared to the one acquired after a single path of light in the magnetic field region. We have reached a precision of a few percent both for Faraday effect and Cotton-Mouton effect. Our measurements give for the first time the experimental value of the Faraday effect at $\lambda$=\,1064\,nm. This value is compatible with the theoretical prediction. Concerning Cotton-Mouton effect, our measurement is the second reported experimental value at this wavelength, and the first to agree at better than 1$\sigma$ with theoretical predictions.