Cotton-Mouton Effect Research Articles

Analysis and improvements of fringe jump corrections by electronics on the JET tokamak far infrared interferometer

For the Tore Supra interferometer phase measurements, an electronics had been developed electronics using field programmable gate array processors. The embedded algorithm can correct the fringe jumps. For comparison, the electronics ran at JET during the 2009 campaign. The first analysis concluded that the electronics was not correcting all the fringe jumps. An analysis of the failures led to improvements in the algorithm, which was tested during the rest of the campaign. In this article, we evaluate the increases in the performance. From the analysis of the remaining faults, further improvements are discussed for designing future boards that are foreseen for JET using the second wavelength and the Cotton–Mouton effect information.

Accuracy of Cotton-Mouton polarimetry in sheared toroidal plasma of circular cross-section

Abstract The Cotton-Mouton effect in sheared plasma with helical magnetic lines is studied on the basis of the equation for complex amplitude ratio (CAR). A simple model for helical magnetic lines in sheared plasma of toroidal configuration is suggested. The equation for CAR in the sheared plasma is solved by perturbation method, using the small shear angle deviations as is characteristic for tokamak plasma. It is shown that the inaccuracy in polarization measurements caused by deviations of the sheared angle amounts to some percentage of the shearless Cotton-Mouton phase shift. One suggested method is to subtract the “sheared” term, which may improve the accuracy of the Cotton-Mouton measurements in the sheared plasma.

ChemInform Abstract: Cotton-Mouton Effect, Magnetic Anisotropy and Charge Delocalization of 2,4,6-Tris(dimethylamino)-1,3,5-triazine (I). Comparison with 1,3,5- Triazine.

ChemInform Abstract: Cotton-Mouton Effect, Magnetic Anisotropy and Charge Delocalization of 2,4,6-Tris(dimethylamino)-1,3,5-triazine (I). Comparison with 1,3,5- Triazine.

FARADAY AND COTTON–MOUTON ROTATIONS IN RELATIVISTIC MEDIUM

The rotation of the polarization vector for light propagating in an external constant magnetic field B in relativistic media is discussed in the two main cases: Faraday and Cotton–Mouton effects. Faraday rotation is circular and arises whenever the medium is not invariant under charge conjugation, whereas Cotton–Mouton rotation arises due to the breaking of the space symmetry in any transparent medium, and describes a sort of ellipse whose axes vary periodically in time from zero to two maximum values. The discussion starts from the expressions for the photon energy eigenvalues in vacuum as well as in a relativistic electron–positron gas, which remain valid in the low energy, low density limits. Values for the rotation frequencies are estimated in some specific cases. Our studies might be of interest both in experimental studies about light propagation in ultrahigh vacuum, as well as in astrophysics.

AXION SEARCH WITH Q & A EXPERIMENT

Dark matter is a focused issue in galactic evolution and cosmology. Axion is a viable particle candidate for dark matter. Its interaction with photon is an effective way to detect it, e.g., pseudoscalar-photon interaction will generate vacuum dichroism in a magnetic field. Motivated to measure the QED vacuum birefringence and to detect pseudoscalar-photon interaction, we started to build up the Q & A experiment (QED [Quantum Electrodynamics] and Axion experiment) in 1994. In this talk, we first give a brief historical account of planet hunting and dark matter evidence. We then review our 3.5 m Fabry-Perot interferometer together with our results of measuring vacuum dichroism and gaseous Cotton-Mouton effects. Our first results give (-0.2 ± 2.8) × 10-13 rad/pass, at 2.3 T with 18,700 passes through a 0.6 m long magnet, for vacuum dichroism measurement. We are upgrading our interferometer to 7 m arm-length with a new 1.8 m 2.3 T permanent magnet capable of rotation up to 13 cycles per second. We aim at [Formula: see text] optical sensitivity with 532 nm cavity finesse around 100,000. When achieved, vacuum dichroism would be measured to 8.6 × 10-17 rad/pass in about 50 days, and QED birefringence would be measured to 28%.

TheIn VivoDiagnosis of Malaria: Feasibility Study Into a Magneto-Optic Fingertip Probe

An in-depth analysis is presented into the feasibility of implementing a new magneto-optic test diagnostic for malaria in the form of a noninvasive finger probe. The diagnostic principle quantifies the malaria pigment hemozoin concentration in the blood stream by measuring the fractional change in transmitted optical intensity arising from the Cotton-Mouton effect on application of a magnetic field. Hemozoin is, to varying degrees, responsive to probing in this manner whether free in the blood plasma following lysis or, more commonly, contained in intracellular vacuoles of erythrocytes or leukocytes. Measurements made on living tissue and sophisticated phantoms, which mix solid and liquid phase media to mimic fingertip physiology, demonstrate that hemozoin concentrations less than 0.02 μg/ml may be readily detectable when blood, caused to pool in the capillary loop arterioles of the extensively vascularized nail bed, is interrogated through the fingernail. On conservative assumptions regarding the relationship between hemozoin production and parasitemia and taking account of the effect of locale on hemozoin responsivity the study indicates that an instrument built on this premise may in principle offer rapid non-invasive detection of malaria at parasitemia levels below 100 parasitized red blood cells per ml.

Control of nonlinear collapse in magnetooptical Kerr media

We demonstrate a novel approach to the control of the collapse of optical beams in Kerr media. To this end, we consider a combination of two magnetooptical (MO) phenomena, the Cotton-Mouton and Faraday effects, in order to introduce a suitable and tunable interplay between the induced linear and circular birefringences. Our numerical analysis confirms that a properly applied external magnetic field may alter the dynamics of the beam propagation in magnetic self-focusing bulk Kerr media. For a chosen value of the optical power, the acceleration, the delay or even the arrest of the collapse can be achieved. We demonstrate experimentally the magnetically-induced acceleration of the collapse in a ferrimagnetic yttrium iron garnet crystal (YIG). Full Text: PDF

Nuclear-spin-induced optical Cotton–Mouton effect in fluids

Relation between the optical detection of NMR signals by the Faraday and Cotton–Mouton effects in fluids and nuclear spin–spin coupling tensors is theoretically explored. An expression is derived for nuclear-spin-induced optical Cotton–Mouton (NSIOC-M) effect from molecules with the prepolarized nuclear magnetic moments. That contains two parts. The temperature independent part is related to hypermagnetizability due to the nuclear magnetic moments. The temperature dependent part is proportional to product between nuclear spin–spin coupling tensors and anisotropy of molecular polarizabilities. NSIOC-M effect can give information on molecular structures in fluids, such as bond lengths and angles. Order of magnitude of the new effect are estimated.

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.

Systematic comparison between line integrated densities measured with interferometry and polarimetry at JET

A systematic comparison between the line integrated electron density derived from interferometry and polarimetry at JET has been carried out. For the first time the reliability of the measurements of the Cotton-Mouton effect has been analyzed for a wide range of main plasma parameters and the possibility to evaluate the electron density directly from polarimetric data has been studied. The purpose of this work is to recover the interferometric data with the density derived from the measured Cotton-Mouton effect, when the fringe jump phenomena occur. The results show that the difference between the line integrated electron density from interferometry and polarimetry is with one fringe (1.143 x 10(19) m(-2)) for more than 90% of the cases. It is possible to consider polarimetry as a satisfactory alternative method to interferometry to measure the electron density and it could be used to recover interferometric signal when a fringe jumps occurs, preventing difficulties for the real-time control of many experiments at the JET machine.

Measurement of the Cotton–Mouton effect in nitrogen, oxygen, carbon dioxide, argon, and krypton with the Q & A apparatus

Experiments for vacuum birefringence and vacuum dichroism have been set up with high-finesse high magnetic experimental apparatuses, which seem to be ideal for small gaseous Cotton–Mouton effect (CME) measurements. PVLAS Collaboration has measured CMEs in krypton, xenon and neon at the wavelength of 1064 nm. In this Letter, we report on our measurement of CMEs in nitrogen, oxygen, carbon dioxide, argon, and krypton at the same wavelength in a magnetic field B = 2.3 T at pressure P = 0.5–300 Torr and temperature T = 295−298 K. Our results agree with the PVLAS results in the common cases.

New precise measurement of the Cotton–Mouton effect in helium

We report a new precise measurement of the Cotton–Mouton effect in helium at T ≃ 290 K for the two wavelengths λ = 532 nm and λ = 1064 nm. The hypermagnetizability anisotropy Δ η for helium is 0.92 ± 0.07 au at the wavelength of 532 nm and 0.98 ± 0.07 au at the wavelength of 1064 nm: these values agree well with the theoretical calculations.

The Cotton-Mouton effect in ferrofluids containing rod-like magnetite particles

Ferrofluids with rod-like nano-sized magnetite particles were prepared by precipitation from aqueous solutions of ferrous hydroxide and aging them in the presence of a magnetic field. We studied the Couton-Mouton effect measuring the azimuthally distribution of the transmitted light intensity and obtained that its magnetic field dependence differs considerably for ferrofluids containing rod-like and spherical magnetic nanoparticles, respectively. After switching off the magnetizing field, the relaxation of the birefringence was observed, measured and analysed.

Analytical calculations of frequency-dependent hypermagnetizabilities and Cotton–Mouton constants using London atomic orbitals

We present the first gauge-origin-independent, frequency-dependent calculations of the hypermagnetizability anisotropy, which determines the temperature-independent contribution to magnetic-field-induced linear birefringence, the so-called Cotton-Mouton effect. A density-matrix-based scheme for analytical calculations of frequency-dependent molecular properties for self-consistent field models has recently been developed, which is also valid with frequency- and field-dependent basis sets. Applying this scheme to Hartree-Fock wave functions and using London atomic orbitals in order to obtain gauge-origin-independent results, we have calculated the hypermagnetizability anisotropy. Our results show that the use of London orbitals leads to somewhat better basis-set convergence for the hypermagnetizability compared to conventional basis sets and that London orbitals are mandatory in order to obtain reliable magnetizability anisotropies.

Real-time electron density measurements from Cotton–Mouton effect in JET machine

Real-time density profile measurements are essential for advanced fusion tokamak operation and interferometry is a proven method for this task. Nevertheless, as a consequence of edge localized modes, pellet injections, fast density increases, or disruptions, the interferometer is subject to fringe jumps, which produce loss of the signal preventing reliable use of the measured density in a real-time feedback controller. An alternative method to measure the density is polarimetry based on the Cotton-Mouton effect, which is proportional to the line-integrated electron density. A new analysis approach has been implemented and tested to verify the reliability of the Cotton-Mouton measurements for a wide range of plasma parameters and to compare the density evaluated from polarimetry with that from interferometry. The density measurements based on polarimetry are going to be integrated in the real-time control system of JET since the difference with the interferometry is within one fringe for more than 90% of the cases.

Short wavelength far infrared laser polarimeter with silicon photoelastic modulators

A short wavelength far infrared laser whose wavelength lambda is about 50 microm is preferable for a polarimeter and an interferometer for high density operations in the Large Helical Device (LHD) and on future large fusion devices such as ITER. This is because the beam bending effect (proportional to lambda(2)) in a plasma, which causes fringe jump errors, is small and the Faraday and the Cotton-Mouton effects are moderate. We have developed a polarimeter with highly resistive silicon photoelastic modulators (PEMs) for the CH(3)OD laser (lambda=57.2 and 47.7 microm). We performed bench tests of the polarimeter with a dual PEM and demonstrated the feasibility for the polarimeter. Good linearity between actual and evaluated polarization angles is achieved with an angular resolution of 0.05 degrees and a temporal resolution of 1 ms. The baseline drift of the polarization angle is about 0.1 degrees for 1000 s.

Forward modeling of JET polarimetry diagnostic

An analytical Bayesian inversion of the JET interferometry line integrated densities into density profiles and associated uncertainty information, is demonstrated. These are used, with a detailed model of plasma polarimetry, to predict the rotation and ellipticity for the JET polarimeter. This includes the lateral channels, for over 45,000 time points over 1313 JET pulses. Good agreement with measured values is shown for a number of channels. For the remaining channels, the requirement of a more detailed model of the diagnostic is demonstrated. A commonly used approximation for the Cotton-Mouton effect on the lateral channels is also evaluated.

Plasma polarimetry with retroreflection

A formalism is described to provide the evolution of the polarization of probing radiation propagating in magnetized plasma where retroreflection is used. It is found that when the retroreflector involves an odd number of reflections, such as occurs in the cube-corner retroreflector, both the Faraday and the Cotton–Mouton effects are additive. However, only in special cases are the effects of the double crossing twice those of a single crossing.

Magnetoelectric birefringence revisited

Electromagnetic wave propagation inside isotropic material media characterized by dielectric coefficients ${\ensuremath{\epsilon}}_{\ensuremath{\mu}\ensuremath{\nu}}(E,B)$ and ${\ensuremath{\mu}}_{\ensuremath{\mu}\ensuremath{\nu}}(E,B)$ is examined. The regime of the eikonal approximation is considered. The Hadamard method of field disturbances is used and the dispersion relations are obtained by solving the Fresnel equation. Some applications of the formalism are presented. Particularly, birefringence phenomena induced by applied external fields are derived and discussed. It is shown that the magnetoelectric birefringence effect can occur even without the presence of Kerr and Cotton-Mouton effects, provided the physical system satisfies certain conditions.

Magnetoelectric Jones spectroscopy of alkali atoms

The Jones effect in a medium of free atoms exposed to static electric and magnetic fields is a useful tool for determining details of an atomic structure. For atoms in their nS ground states irradiated by a monochromatic wave in resonance with a single-photon transition to an n′ D state, the bilinear Jones effect is not shaded by the quadratic Kerr and Cotton–Mouton effects, nor by the linear in magnetic field Faraday effect. The position and shape of the amplitude resonance may provide information on spectroscopic properties of atomic levels. We generalize equations for the Jones-effect amplitude to the case of a doublet structure of energy levels and calculate corresponding parameters for alkali atoms. General equations are derived for the amplitude dependence on the relative orientation of the static electric and magnetic fields and on the angle between the static field and the major axis of the wave polarization vector. These equations demonstrate explicitly that the three bilinear-in-static-fields optical birefringence effects—(i) the Jones birefringence (in parallel fields), (ii) the linear birefringence and (iii) the directional birefringence (the last two in perpendicular fields)—correspond to particular cases of the bilinear-in-static-fields correction to the amplitude of Rayleigh forward scattering.