No description available.

No description available.

A suspended ionic solution of 1-butyl-3-methylimidazolium iron tetrachloride [BMIM][FeCl4] provides a novel medium for achieving Faraday rotation under small magnetic fields at pump wavelengths of 980nm. As verified with spectrophotometry, transmission at telecommunication wavelengths makes the solution applicable across multiple applications. A cryostation was used to measure the sample up to a 340K and under field at 600mT, the ionic sample shows the necessary temperature stability and enables compact formats suitable for potential industrial applications. With a rotation of linearly polarized light of 0.04° over a 450um path length, a full 45° rotation requires only a 50.6cm path length and with only a 0.000175°/K temperature dependence. The observation of polarization effects in real time using lock-in amplifiers, and a photo-elastic modulator demonstrates the scalability, responsiveness, and stability of the ionic liquids for photonic integration. The test set up provides a convenient way to expand the research on ionic liquid Faraday rotation materials and other Faraday liquids ideally leading to a compact in-line isolator solution.

Knowledge of the coronal magnetic field is crucial for understanding (1) the heating mechanism(s) of the solar corona, (2) the acceleration of the fast solar wind, and (3) the structure and dynamics of coronal mass ejections (CMEs). Observation of Faraday rotation (FR) is one of the best remote-sensing techniques for determining plasma properties in the corona and can provide information on the plasma structure of a CME shortly after launch, shedding light on the initiation process. I used the Karl G. Jansky Very Large Array (VLA) to make sensitive Faraday rotation measurements to investigate the general plasma structure of the corona, properties of coronal plasma inhomogeneities and waves, and transients associated with coronal mass ejections. To enhance my measurements of FR transients, I also developed an algorithm in the Common Astronomy Software Applications (CASA) package to mitigate ionospheric Faraday rotation. In August, 2011, I made FR observations at 5.0 and 6.1 GHz of the radio galaxy 3C 228 through the solar corona at heliocentric distances of 4.6 - 5.0 solar radii using the VLA. Observations at 5.0 GHz permit measurements deeper in the corona than previous VLA observations at 1.4 and 1.7 GHz. These FR observations provided unique information on the magnetic field in this region of the corona. My data on 3C 228 provide two lines of sight (separated by 46 arcseconds, 33,000 km in the corona). I detected three periods during which there appeared to be a difference in the Faraday rotation measure between these two closely spaced lines of sight, which I used to estimate coronal currents; these values (ranging from 2.6 to 4.1 GA) are several orders of magnitude below that which is necessary for significant coronal heating (assuming the Spitzer resistivity). I also used the data to determine upper limits (3.3 and 6.4 rad/m⁻²along the two lines of sight) on FR fluctuations caused by coronal waves. These upper limits are comparable to and, thus, not inconsistent with the theoretical models for Alfvén wave heating of the corona by Hollweg et al. (2010). To support the needs of the low frequency radioastronomical community as well as my own research of coronal FR transients, I developed a new calibration algorithm for CASA that uses GPS-based global ionosphere maps of the Total Electron Content (TEC) to mitigate ionospheric Faraday rotation. The Earth's ionosphere introduces direction- and time-dependent effects over a range of physical and temporal scales and so is a major source for unmodeled phase offsets for low frequency radioastronomical observations. It has become common practice to use global ionospheric models derived from the Global Positioning System (GPS) to provide a means of externally calibrating low frequency data. However, CASA, which was developed to meet the data post-processing needs of next generation telescopes such as the VLA and the Atacama Large Millimeter/submillimeter Array (ALMA), did not have the capability to make ionospheric corrections before I implemented this calibration algorithm. I investigated several data centers as potential sources for global ionospheric models and chose the International Global Navigation Satellite System Service data product because data from other sources are generally too sparse to use without additional interpolation schemes. I employed these ionospheric corrections in reducing VLA observations made in August, 2012, at 1 - 2 GHz of a “constellation” of radio sources through the solar corona at heliocentric distances that ranged from 5 - 15 solar radii. Of the nine sources observed, three were occulted by CMEs: 0842+1835, 0900+1832, and 0843+1547. In addition to my radioastronomical observations, which represent one of the first active hunts for CME Faraday rotation since Bird et al. (1985) and the first active hunt using the VLA, I obtained white-light coronagraph images from the LASCO/C3 instrument aboard SOHO to determine the Thomson scattering brightness, BT. BT is proportional to the electron plasma density and provides a means to independently estimate the plasma density and determine its contribution to the observed Faraday rotation. A constant density force-free flux rope embedded in the background corona was used to model the effects of the CMEs on BT and FR. In the case of 0842+1835, the flux rope model underestimated the peak value in BT and did not reproduce the decreasing BT inside the inner cavity region of the CME; however, there was satisfactory agreement between the model and the observed FR. The single flux rope model successfully reproduces both the observed BT and FR profiles for 0900+1832. 0843+1547 was occulted by two CMEs. Therefore, I modeled observations of 0843+1547 using two flux ropes embedded in the background corona. The two flux rope model successfully reproduces both BT and FR profiles for 0843+1547 and, in particular, the two flux rope model successfully replicates the appropriate slope in FR before and after occultation by the second CME and predicts the observed change in sign to FR > 0 at the end of the observing session. I briefly discuss the plasma densities ( 6 - 22 x 10³ cm⁻³) and axial magnetic field strengths (2 - 12 mG) inferred from my models and compare them to the modeling work of Liu et al. (2007) and Jensen et al. (2008), as well as previous CME FR observations by Bird et al. (1985).

The advancement of photonics technologies depends on synthesis of novel materials and processes for device fabrication. The characterization techniques of the optical, electrical and magnetic properties of the synthesized materials and devices, by non-contact, non-invasive and nondestructive methods plays a significant role in development of new photonics technologies. The research reported in this thesis focuses on two such aspects of photonic materials characterization: Magneto-Optic characterization and Spectroscopic Ellipsometry. The theoretical and experimental basis of these two techniques, and experimental data analysis are presented in two parts. In Part 1, the changes in magneto-optic parameters of FePT PS-P2VP block copolymer nanocomposites with increasing concentrations of FePt nanoparticles in the block copolymer are analyzed. We present the results of change in MO anisotropy factor with the wt% of FePt and try to analyze these changes with further experimentation. Part 2 presents the results of spectroscopic ellipsometry of group III-IV multilayered thin film materials to give their precise thicknesses and optical constants. Both these techniques are unique ways to understand novel material characteristics for future use in device development.

O spin de um elétron confinado em uma ilha quântica (do inglês, quantum dot ou QD) oferece a oportunidade de armazenamento e manipulação de coerência de fase em escalas fe tempo muito mais longas do que aquelas encontradas em dispositivos convencionais. A natureza zero-dimensional dessas estruturas pode ser explorada em dispositivos optoeletrônicos baseados na manipulação de spin pela luz, tais como QD lasers,emissores de fóton-único e transistores de elétron-único. Desta maneira, o entendimento da física por trás do controle do magnetismo pela luz torna-se essencial no avanço do campo de manipulação de spin e no desenvolvimento de aparelhos tecnológicos. Em particular, o enfoque dessa tese, se refere à geração induzida de magnetização em um conjunto de ilhas quânticas, mediante a iluminação por um pulso de luz circularmente polarizado ressonante com a energia de transição dos QD\'s. Neste trabalho em questão, dois modelos quânticos para a magnetização induzida pela luz são apresentados. Para ambos os modelos, a fase de precessão da magnetização em função do campo magnético apresentou excelente concordância com os dados experimentais referentes a um conjunto de ilhas quânticas carregadas de (In, Ga)As. Demonstramos ainda, que a precessão do buraco participante do tríon desempenha um papel fundamental na determinação da amplitude e fase da precessão da magnetização. Ressaltamos também a aplicabilidade do modelo na descrição de ilhas carregadas positivamente. E por fim, sugerimos que a teoria desenvolvida pode ser utilizada como técnica de medição do tempo de vida ressonante do tríon em função da energia de emissão do QD. / The spin of an electron confined in a quantum dot (QD) offers the opportunity to store and manipulate phase coherence over much longer time scales than it is typically possible in charge based devices. The zero-dimensional nature of these nanostructures can be exploited in optoeletronic devices, such as quantum dot laser, single-photon emitters, single-electron transistor and spin-manipulation. Thus, understanding the physics behind light control of magnetism is essential to advance this field and device applications based on it. In particular, magnetization generation can be induced in an ensemble of quantum dots, each charged with a single electron, when illuminated with a short circularly polarized light pulse resonant with the fundamental gap of the QDs. In this work, two quantum-mechanical models for the light-induced magnetization are presented. For both models, the phase of magnetization precession as a function of the strength of the magnetic field in a Voigt geometry is in excellent agreement with experimental data measured on (In, Ga)As singly charged quantum dot ensemble. It is demonstrated that the precession of the hole in the trion plays a vital role because it determines the amplitude and phase of the magnetization precession. The model could also be easily extended to describe positively charged quantum dots. We also suggest that our theory, can be used as technique to measure the resonante trion lifetime as a function of QD emission energy.

Neste trabalho, são apresentados os resultados experimentais de medições de densidade eletrônica no tokamak TBR-l, obtidas por meio de rotação de Faraday num feixe de micro-ondas. O feixe (65 GHz, 500 m W) é gerado por uma klystron e atravessa o plasma no plano médio horizontal. Os valores obtidos para a densidade concordam bem com as medições feitas com um interferômetro de micro-onda o; convencional. A partir das simulações numéricas e das medições, conclui-se ser recomendável o uso de comprimentos de onda menores, para minimizar a refração do feixe no plasma, Os resultados obtidos demonstram a viabilidade do método de medição de densidade por rotação de Faraday. em experiência feita pela primeira vez em tokamak, para a geometria considerada. / In this work, the experimental results of electronic density measurements in the TBR-l tokamak, obtained by Faraday rotation of a microwave beam, are presented. The beam (65 GHz, 500 mW) is generated by a klystron and crosses the plasma in the horizontal plane. The density values obtained are in agreement with the measurements of a conventional microwave interferometer. As a result of numerical simulations and measurements, it can be concluded that it would be advisable the use of lower wavelengths, to minimize the beam refraction when it crosses the plasma. The results show the feasability of the Faraday rotation method for density measurement, in the first experiment performed in a tokamak for the geometry considered.

Neste trabalho, são apresentados os resultados experimentais de medições de densidade eletrônica no tokamak TBR-l, obtidas por meio de rotação de Faraday num feixe de micro-ondas. O feixe (65 GHz, 500 m W) é gerado por uma klystron e atravessa o plasma no plano médio horizontal. Os valores obtidos para a densidade concordam bem com as medições feitas com um interferômetro de micro-onda o; convencional. A partir das simulações numéricas e das medições, conclui-se ser recomendável o uso de comprimentos de onda menores, para minimizar a refração do feixe no plasma, Os resultados obtidos demonstram a viabilidade do método de medição de densidade por rotação de Faraday. em experiência feita pela primeira vez em tokamak, para a geometria considerada. / In this work, the experimental results of electronic density measurements in the TBR-l tokamak, obtained by Faraday rotation of a microwave beam, are presented. The beam (65 GHz, 500 mW) is generated by a klystron and crosses the plasma in the horizontal plane. The density values obtained are in agreement with the measurements of a conventional microwave interferometer. As a result of numerical simulations and measurements, it can be concluded that it would be advisable the use of lower wavelengths, to minimize the beam refraction when it crosses the plasma. The results show the feasability of the Faraday rotation method for density measurement, in the first experiment performed in a tokamak for the geometry considered.

Knowledge of energy dissipation and relaxation in electron, spin, and lattice degrees of freedom is of fundamental importance from both a technological and scientific point of view. In this dissertation, the electronic and magnetization dynamics of photoexcited colloidal cobalt substituted iron oxide nanocrystals, CoxFe3-xO4, were investigated through transient absorption and pump-probe Faraday rotation measurements. In this dissertation, linearly polarized femtosecond optical pulses at 780 nm were used to excite the weak absorption originating from the intervalence charge transfer transition (IVCT) between Fe2+ and Fe3+ ions of Fe3O4 nanocrystals. The timescale and corresponding relaxation processes of electronic relaxation dynamics of the excited IVCT state were first discussed. Size effect on electronic relaxation dynamics in Fe3O4 nanocrystals is not distinct on the basis of result from this study. One interesting feature of electronic dynamics data of photoexcited Fe3O4 nanocrystals is the creation of coherent acoustic phonons. Information on lattice temperature was obtained by measuring the period of coherent acoustic phonon as a function of excitation fluence and fit into a simple model based on Lamb’s theory. Since optical control of the magnetization can be either through optical or heating mechanisms, quantitative estimation of degree of demagnetization caused by lattice temperature is made by using Langevin function. The result from such estimation indicates the effect of lattice temperature rise on magnetization is too small to significantly affect the magnetization of Fe3O4 nanocrystals. Magnetization dynamics were studied via pump-probe Faraday rotation measurements. Optical excitation with near-infrared pulse resulted in an ultrafast demagnetization in 100fs. The energy of the excited state then relaxed through spin-lattice relaxation (SLR). Effects of surface spin and chemical tuning on the SLR were investigated by comparing the magnetization recovery timescales of nanocrystal with different particle sizes and cobalt concentration respectively. The experimental result is explained by a simple model where interior and surface spins contributed to the spin-lattice relaxation process differently. The observations suggest that spin-orbit coupling of the surface is stronger and less sensitive to stoichiometric variation than the interior spins of the nanocrystals.

The main aim of this work was to develop a method of screening HgCdTe materials for carrier concentration and mobility using Faraday rotation θ and absorption α. Faraday rotation provides N/m*2, where N is the carrier concentration and m* is the effective mass. Since m* was not known in HgCdTe, a Faraday rotation spectrometer was developed to systematically measure it as a function of temperature and Cd mole fraction. Effective masses in n-InSb, and n-GaAs were measured and compared with known values in the literature to validate the method. Mobility is proportional to θ/α. The proportionalities were determined in HgCdTe, n-InSb, and n-GaAs at infrared wavelengths. The dissertation consists of the preface, introduction, three chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian).