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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nonlinear coupling of left and right handed circularly polarized dispersive Alfvén wave

The nonlinear phenomena are of prominent interests in understanding the particle acceleration and transportation in the interplanetary space. The ponderomotive nonlinearity causing the filamentation of the parallel propagating circularly polarized dispersive Alfvén wave having a finite frequency may be one of the mechanisms that contribute to the heating of the plasmas. The contribution will be different of the left (L) handed mode, the right (R) handed mode, and the mix mode. The contribution also depends upon the finite frequency of the circularly polarized waves. In the present paper, we have investigated the effect of the nonlinear coupling of the L and R circularly polarized dispersive Alfvén wave on the localized structures formation and the respective power spectra. The dynamical equations are derived in the presence of the ponderomotive nonlinearity of the L and R pumps and then studied semi-analytically as well as numerically. The ponderomotive nonlinearity accounts for the nonlinear coupling between both the modes. In the presence of the adiabatic response of the density fluctuations, the nonlinear dynamical equations satisfy the modified nonlinear Schrödinger equation. The equations thus obtained are solved in solar wind regime to study the coupling effect on localization and the power spectra. The effect of coupling is also studied on Faraday rotation and ellipticity of the wave caused due to the difference in the localization of the left and the right modes with the distance of propagation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2006

Polarization Rotation and the Third Stokes Parameter: The Effects of Spacecraft Attitude and Faraday Rotation

The third Stokes parameter of ocean surface brightness temperatures measured by the WindSat instrument is sensitive to the rotation angle between the polarization vectors at the ocean surface and the instrument. This rotation angle depends on the spacecraft attitude (roll, pitch, yaw) as well as the Faraday rotation of the electromagnetic radiation passing through the Earth's ionosphere. Analyzing the WindSat antenna temperatures, we find biases in the third Stokes parameter as function of the along-scan position of up to 1.5 K in all feedhorns. This points to a misspecification of the reported spacecraft attitude. A single attitude correction of -0.16deg roll and 0.18deg pitch for the whole instrument eliminates all the biases. We also study the effect of Faraday rotation at 10.7 GHz on the accuracy of the third Stokes parameter and the sea surface wind direction retrieval and demonstrate how this error can be corrected using values from the International Reference Ionosphere for the total electron content when computing Faraday rotation.

Meissner, Thomas↗
DOE OSTI2015

Study of ablation and implosion stages in wire arrays using coupled ultraviolet and X-ray probing diagnostics

Star and cylindrical wire arrays were studied using laser probing and X-ray radiography at the 1-MA Zebra pulse power generator at the University of Nevada, Reno. The Leopard laser provided backlighting, producing a laser plasma from a Si target which emitted an X-ray probing pulse at the wavelength of 6.65 Å. A spherically bent quartz crystal imaged the backlit wires onto X-ray film. Laser probing diagnostics at the wavelength of 266 nm included a 3-channel polarimeter for Faraday rotation diagnostic and two-frame laser interferometry with two shearing interferometers to study the evolution of the plasma electron density at the ablation and implosion stages. Dynamics of the plasma density profile in Al wire arrays at the ablation stage were directly studied with interferometry, and expansion of wire cores was measured with X-ray radiography. The magnetic field in the imploding plasma was measured with the Faraday rotation diagnostic, and current was reconstructed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1961

A General Computer Program for Ionospheric Ray-Tracing

The study of the ionosphere using the Faraday rotation effect has been undertaken recently by means of rocket, satellite, and moon echo experiments. Different approximations have been used by different authors, resulting in methods with different degrees of complexity, and it is possible to say that the more accurate a method is, the more difficult its application becomes. However, the use of modern high-speed digital computers offers the possibility of using more complex methods in the solution of this problem, The program described in this report was written for the ILLIAC, the digital computer of the University of Illinois. Only the general features common to most digital computers will be mentioned. This program was prepared having in mind the analysis of the Faraday rotation effect, as recorded from artificial satellites. It is intended to be as general as possible in the conditions imposed on the assumed propagating medium: specifically there are no restrictions on the models of the electron density distribution and the earth's magnetic fields. long as the ray theory Ls valid. The program will trace separately the ordinary and the extraordinary mode, and it will find the virtual phase path length of a ray of each mode between the transmitter (satellite) and a receiver (station). The difference between respective phase path-lengths is related to the Faraday rotation through a constant which depends on the frequency.

Gonzales, Victor H.↗
NASA NTRS1998

An Investigation of Magneto-Optical Effects

We exhibit the effects of Faraday rotation on the direction of the transverse component of the magnetic field in a simple, symmetric sunspot. A set of 35 polarization filtergrams of NOAA active region 4662 (June 9, 1985) were obtained with the Marshall Space Flight Center (MSFC) vector magnetograph. These filtergrams measured the Stokes I, Q, U, and V intensities averaged over the instrument's filter bandpass (0.0125 nm) for wavelengths from 0.017 nm in the red wing to 0.017 nm in the blue wing of the Lambda525.22 nm spectral line in steps of 0.001 nm. These data were used to derive the azimuth phi of the vector field as a function of wavelength over the field of view of the sunspot. We interpret the observed variations of this azimuth with wavelength as the effects of Faraday rotation and verify this interpretation by comparing these variations with those predicted from magneto-optical theory. In the theoretical calculations we use the line-profile parameters and magnetic field strength derived in previous work by Balasubramaniam and West (Astrophys. J 382, p. 699, 1991).

Adams, Mitzi L.↗
DOE OSTI2017

The Co-evolution of a Magnetized Intracluster Medium and Hot Galactic Coronae: Magnetic Field Amplification and Turbulence Generation

We use adaptive-mesh magnetohydrodynamic simulations to study the effect of magnetic fields on ram pressure stripping of galaxies in the intracluster medium (ICM). Although the magnetic pressure in typical clusters is not strong enough to affect the gas mass loss rate from galaxies, magnetic fields can affect the morphology of stripped galaxies. ICM magnetic fields are draped around orbiting galaxies and aligned with their stripped tails. Magnetic fields suppress shear instabilities at the galaxy-ICM interface, and magnetized tails are smoother and narrower than tails in comparable hydrodynamic simulations in Vijayaraghavan and Ricker. Orbiting galaxies stretch and amplify ICM magnetic fields, amplifying magnetic power spectra on 10–100 kpc scales. Galaxies inject turbulent kinetic energy into the ICM via their turbulent wakes and g-waves. The magnetic energy and kinetic energy in the ICM increase up to 1.5--2 Gyr of evolution, after which galaxies are stripped of most of their gas, and do not have sufficiently large gaseous cross sections to further amplify magnetic fields and inject turbulent kinetic energy. The increase in turbulent pressure due to galaxy stripping and generation of g-waves results in an increase in the turbulent volume fraction of the ICM. This turbulent kinetic energy is not a significant contributor to the overall ICM energy budget, but greatly impacts the evolution of the ICM magnetic field. Additionally, the effect of galaxies on magnetic fields can potentially be observed in high resolution Faraday rotation measure (RM) maps as small-scale fluctuations in the RM structure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Optically induced magnetic polarons in EuTe

Direct measurements of the photoinduced magnetization in EuTe, using a two color pump-and-probe technique, are presented. The photoinduced effect was pumped using photons of above-the-bandgap energy, and detected by the Faraday rotation of a probe beam of energy below-the-bandgap. The photoinduced Faraday rotation changes sign, as expected from our model for the optically induced magnetic polaron. The EuTe spin-flop transition at low fields is also detected as a sharp step in the photoinduced Faraday rotation, and its observation provides additional supports for the photoinduced polaron model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Zinc oxide based diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, microstructural and optical properties

Nanoparticles of ZnO and ZnO doped with transition metals (Mn, Co) were synthesized by laser ablation in liquid medium. Scanning electron microscopy (SEM) showed formation of nanostructures with different shapes. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. Absorption edge of ZnO, ZnO:Mn and ZnO:Co colloidal nanoparticles exhibits blue shift due to confinement effect. In photoluminescence spectra three peaks are attributed to the band-edge transitions and defect states. The Faraday rotation in ZnO:Mn nanoparticles gives evidence for paramagnetic behavior at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Plasma physics in strong-field regimes: Theories and simulations

In strong electromagnetic fields, unique plasma phenomena and applications emerge whose description requires recently developed theories and simulations [Y. Shi, Ph.D. thesis, Princeton University (2018)]. In the classical regime, to quantify effects of strong magnetic fields on three-wave interactions, a convenient formula is derived by solving the fluid model to the second order in general geometry. As an application, magnetic resonances are exploited to mediate laser pulse compression, whereby higher intensity pulses can be produced in wider frequency ranges, as confirmed by particle-in-cell simulations. In even stronger fields, relativistic-quantum effects become important, and a plasma model based on scalar quantum electrodynamics (QED) is developed which unveils observable corrections to Faraday rotation and cyclotron absorption in strongly magnetized plasmas. Beyond the perturbative regime, lattice QED is extended as a numerical tool for plasma physics, using which the transition from wakefield acceleration to electron-positron pair production is captured when laser intensity exceeds the Schwinger threshold.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A method for eliminating Faraday rotation in cryostat windows in longitudinal magneto-optical Kerr effect measurements

A solution to the problem of disturbing effect of the background Faraday rotation in the cryostat windows on longitudinal magneto-optical Kerr effect (LMOKE) measured under vacuum conditions and/or at low temperatures is proposed. The method for eliminating the influence of Faraday rotation in cryostat windows is based on special arrangement of additional mirrors placed on sample holder. In this arrangement, the orientation of the cryostat window is perpendicular to the light beam direction and parallel to an external magnetic field generated by the H-frame electromagnet. The operation of the LMOKE magnetometer with the special sample holder based on polarization modulation technique with a photo-elastic modulator is theoretically analyzed with the use of Jones matrices, and formulas for evaluating of the actual Kerr rotation and ellipticity of the sample are derived. The feasibility of the method and good performance of the magnetometer is experimentally demonstrated for the LMOKE effect measured in Fe/Au multilayer structures. The influence of imperfect alignment of the magnetometer setup on the Kerr angles, as derived theoretically through the analytic model and verified experimentally, is examined and discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1989

Effects of irregularity anisotropy on Faraday polarization fluctuations

The previous model (Lee et al., 1982) of the Faraday polarization fluctuations (FPF) is extended after taking into account the anisotropic nature of the commonly observed, rodlike and sheetlike ionospheric irregularities. Striking effects of irregularity anisotropy are found in the longitudinal radio propagation. However, if the wave propagation angle is not small (say, greater than 5 deg), the effects of irregularity anisotropy on FPF introduced by rodlike irregularities weaken significantly, while those caused by sheetlike irregularities remain prominent. Therefore, under the same ionospheric propagation conditions, sheetlike ionospheric irregularities are more effective than rodlike ionospheric irregularities in causing the FPF of radio waves. It is expected that intense FPF of VHF radio signals can be observed not only near the equatorial anomaly but also in the auroral region.

Lee, M. C.↗
NASA NTRS2013

Ionospheric Specifications for SAR Interferometry (ISSI)

The ISSI software package is designed to image the ionosphere from space by calibrating and processing polarimetric synthetic aperture radar (PolSAR) data collected from low Earth orbit satellites. Signals transmitted and received by a PolSAR are subject to the Faraday rotation effect as they traverse the magnetized ionosphere. The ISSI algorithms combine the horizontally and vertically polarized (with respect to the radar system) SAR signals to estimate Faraday rotation and ionospheric total electron content (TEC) with spatial resolutions of sub-kilometers to kilometers, and to derive radar system calibration parameters. The ISSI software package has been designed and developed to integrate the algorithms, process PolSAR data, and image as well as visualize the ionospheric measurements. A number of tests have been conducted using ISSI with PolSAR data collected from various latitude regions using the phase array-type L-band synthetic aperture radar (PALSAR) onboard Japan Aerospace Exploration Agency's Advanced Land Observing Satellite mission, and also with Global Positioning System data. These tests have demonstrated and validated SAR-derived ionospheric images and data correction algorithms.

Pi, Xiaoqing↗
NASA NTRS1979

Rocket radio measurement of electron density in the nighttime ionosphere

One experimental technique based on the Faraday rotation effect of radio waves is presented for measuring electron density in the nighttime ionosphere at midlatitudes. High frequency linearly-polarized radio signals were transmitted to a linearly-polarized receiving system located in a spinning rocket moving through the ionosphere. Faraday rotation was observed in the reference plane of the rocket as a change in frequency of the detected receiver output. The frequency change was measured and the information was used to obtain electron density data. System performance was evaluated and some sources of error were identified. The data obtained was useful in calibrating a Langmuir probe experiment for electron density values of 100/cu cm and greater. Data from two rocket flights are presented to illustrate the experiment.

Gilchrist, B. E.↗
DOE OSTI2021

Dynamic Nuclear Polarization Enhanced Nuclear Spin Optical Rotation

Here, nuclear spin optical rotation (NSOR) has been investigated as a magneto-optical effect, which holds the potential for applications, including hybrid optical-nuclear magnetic resonance (NMR) spectroscopy and gradientless imaging. The intrinsic nature of NSOR renders its detection relatively insensitive, which has prevented it moving from a proof of concept to a method supporting chemical characterizations. In this work, the dissolution dynamic nuclear polarization technique is introduced to provide nuclear spin polarization, increasing the signal-to-noise ratio by several thousand times. NSOR signals of 1 H and 19 F nuclei are observed in a single scan for diluted compounds, which has made this effect suitable for the determination of electronic transitions from a specific nucleus in a large molecule.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1992

On neutralized currents in the solar corona

Using Ampere's integral law applied to vector magnetograph transverse field data, the current pattern in an active region associated with flaring activity is analyzed. The greater sensitivity of this integral formalism of Ampere's law may allow one to identify regions of weak return current around the actual positive current region. The effects of Faraday rotation on the inferred magnetic field measurements, and hence on the deduced current pattern, are discussed. It is concluded that the current patterns in the region consist either of a neutralized current system, well modeled by a coaxial cable, or of a potential field, with the apparent currents in the core an artifact induced by magneto-optical effects. In either case, the data do not convincingly show an unneutralized current system.

Wilkinson, Ladye K.↗
DOE OSTI2020

A graphene-based magnetoplasmonic metasurface for actively tunable transmission and polarization rotation at terahertz frequencies

The rise of terahertz (THz)-based technologies has prompted intense interest in methods for manipulating the properties of THz radiation. In this Letter, we experimentally demonstrate a graphene micro-ribbon-based metasurface that allows us to tailor and dynamically tune the transmission and polarization rotation spectra of impinging THz pulses. This is achieved by controlling the geometry of the ribbon pattern and the applied DC magnetic field, both of which strongly influence the magnetoplasmonic response of the metasurface. The properties of the metasurface can be accurately modeled using an effective medium approach that considers the capacitive interaction of the ribbons resulting from the THz electric field. Furthermore, our results highlight the promise of graphene-based THz devices that leverage the strongly enhanced light–matter interactions resulting from patterning.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Study of magneto-optic effect on Mn{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4} nanoferrofluids

Mn{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4} nanoparticles (with x varying as 0.1, 0.3, 0.5, 0.7 and 0.9) have been synthesized by co- precipitation method using polyvinyl alcohol as surfactant. Structural analysis and surface morphology of the samples were analysed using X-ray diffraction and scanning electron microscope respectively. The Scherer approximation was used to obtain crystallite sizes and found to decrease from 8.9 nm to 4.3 nm with increase in zinc substitution. The chemical composition of samples obtained through EDAX was comparable with the initial substitutions. Saturation magnetization (M{sub s}), Remanence (M{sub r}) and Coercivity (H{sub c}) were measured using VSM at room temperature and found to decrease with increase in zinc substitution. Verdet constant of the samples are obtained from Faraday rotation for various magnetic fields and it varies from 18 × 10{sup −4} to 3 × 10{sup −4}deg/Gcm with zinc substitution.

77 NANOSCIENCE AND NANOTECHNOLOGY↗