Neste trabalho estudamos, experimental e teoricamente, as flutuações de campos eletromagnéticos após a interação com sistemas atómicos em configuração de dois níveis com degenerescências. Estes sistemas atómicos eram preparados em superposições coerentes de seus estados obtidas através dos fenômenos de Transparência e Absorção Eletromagneticamente Induzidas. O sistema físico foi considerado em dois modelos teóricos semiclássicos distintos: resposta atómica linear e difusão de fase. Estes modelos se baseiam no fato de que lasers de díodo possuem excesso de ruído na fase, que durante o processo de interação coerente com o sistema atómico é transferido ressonantemente para o ruído de intensidade. Em nossa análise, observamos resultados não triviais em relação aos sinais de ruído e correlação entre os campos medidos. Verificamos que, num vapor atómico, a largura Doppler associada à transição tem um papel fundamental na composição elo sinal ele ruído. Observamos que mesmo transições que, a priori, estariam não ressonante podem ter contribuição significativa para o sinal ele ruído. Os modelos teóricos desenvolvidos apresentaram um bom acordo qualitativo com parte dos dados experimentais e se mostraram uma ferramenta útil para a análise da influência dos efeitos coerentes nas flutuações elos campos, quando o laser possui excesso de ruído ele fase. / We present a theoretical and experimental investigation of the fluctuations of electromagnetic fields after the interaction with degenerate two-level atomic systems. These atomic systems were prepared in coherent superpositions of the states obtained through Electromagnetically Induced Transparency (EIT) and Absorption (EIA). The physical system was studied in two semi-classical models: linear atomic response and phase diffusion. These models are based on the fact that diode lasers have excess phase noise, which in the interaction process is transferred to intensity noise. We observed non trivial results about the noise signals and the correlations between the fields. We showed that, in atomic vapor, the Doppler width has a fundamental role in the origin of the noise signal. The theoretical models show good qualitative agreement with part of the experimental result features and are a powerful tool to analyze field fluctuations, when the laser has excess phase noise.

The determination of plasma equilibrium profiles is necessary to evaluate the properties of the confinement and to investigate perturbation effects. Optical diagnostics can be used to determine some of these profiles. However, these diagnostics measure all emitted radiation at a solid angle that illuminate each diagnostic channel through a slit. Therefore, the real measured quantity is the emissivity integrated along the line-of-sight and some unfolding procedure, like Abels inversion, is commonly used to recover the emissivity profile. In TCABR tokamak, at the Physics Institute of the University of São Paulo, a 24-channel bolometer and a 20-channel soft X-ray optical diagnostics are used to measure the plasma emissivity in wavelength range from 1.0 to 1000 nm, depending on the used filters. In this work, a numerical simulation is used to compute the signal measured by the diagnostics for a given emissivity profile, allowing direct comparison with the experimental data and avoiding the use of the Abel\'s inversion directly and the numerical difficulties associated with unfolding procedures. By considering TCABR tokamak geometry, spatial coordinates can be related to the normalized linear coordinates of the plasma by imposing a plasma emissivity model that depends on some free parameters, allowing the emissivity resulting in each point can be calculated. Thus, the luminosity of each channel is calculated by the integral of the emissivity modeled in each line-of-sight (Radon Transformation). Emissivity model free parameters are determined by fitting calculated luminosity to measured one. We considered three types of emissivity profiles: a parabolic model in law of power, a Gaussian model and a model based on Bessel functions. We observed that the parabolic profile fits well the bolometer data, while the Gaussian profile is adequate to describe the data obtained with the soft X-ray detector. / A determinação dos perfis de equilíbrio do plasma é necessária para avaliar as propriedades do confinamento e para investigar os efeitos de perturbações. Diagnósticos ópticos podem ser usados para determinar alguns desses perfis. No entanto, esses diagnósticos medem toda a radiação luminosa emitida em um ângulo sólido que ilumina cada canal do detector através de uma fenda. Assim, a verdadeira grandeza física medida é a emissividade integrada ao longo da linha de visada. Com isso, algum procedimento de deconvolução, como a inversão de Abel, se faz necessário para obter o perfil de emissividade. No tokamak TCABR do Instituto de Física da USP, um bolômetro de 24 canais e um detector de raios-X moles de 20 canais são utilizados para medir a emissividade do plasma no intervalo de comprimento de onda de 1 a 1.000 nm, dependendo dos filtros utilizados. Neste trabalho, uma simulação numérica é usada para calcular o sinal medido pelos diagnósticos para um dado perfil de emissividade, possibilitando a comparação direta com os dados experimentais, evitando a realização da inversão de Abel e os problemas numéricos associados aos procedimentos de deconvolução. Pela consideração da geometria do tokamak TCABR, as coordenadas espaciais podem ser relacionadas com as coordenadas lineares normalizadas do plasma por meio da imposição de um modelo de emissividade para o plasma que dependa de alguns parâmetros livres, permitindo que a emissividade resultante em cada ponto possa ser calculada. Assim, a luminosidade de cada canal é calculada pela integral da emissividade modelada em cada linha de visada (Transformada de Radon). Os parâmetros livres dos perfis de emissividade são determinados ajustando-se as luminosidades calculadas em termos das luminosidades medidas. Nós consideramos três modelos de perfis de emissividade: um modelo parabólico em lei de potência, um modelo gaussiano e um modelo baseado em funções de Bessel. Observamos que o perfil parabólico ajusta-se bem aos dados do bolômetro, ao passo que o perfil gaussiano é adequado para descrever os dados obtidos com o detector de raios-X moles.

Doctor of Philosophy / Department of Physics / Daniel Rolles / Modern laser sources can produce bursts of light that surpass even the fastest molecular vibrations. With durations this short even moderate pulse energies generate peak powers exceeding the average power output of the entire globe. When focused, this can result in an ultrafast electric field greater than the Coulomb potential that binds electrons to nuclei. This strong electric field strips electrons away from atoms in a process known as strong-field ionization. The first experimental realization of photoionization with intense laser pulses occurred only a few years after the invention of the laser. Yet, despite decades of intensive investigation, open questions remain. At the same time, the knowledge gained has led to the creation of multiple exciting fields such as attoscience, femtochemistry, and ultrafast nano-photonics. In this thesis I present my work to advance the fundamental understanding of intense, ultrafast light-matter interactions as well as efforts to expand the technological capabilities of ultrafast light sources and measurement techniques. This includes the photoionization pro- cess of atoms and nanoparticles subject to intense, mid-infrared laser fields. The resulting photoelectron emission is measured, with high precision, in a velocity map imaging spec- trometer. Other parts of this thesis detail my work on the generation and characterization of non-Gaussian optical pulses. Femtosecond Bessel beams are used to drive and study high harmonic generation with the ultimate goal of creating a compact, high-flux XUV source. Further studies include few-cycle pulses and the carrier-envelope phase, specifically methods of locking and tagging the carrier-envelope phase. A single-shot, all optical tagging method is developed and directly compared to the standard tagging method, the carrier-envelope phase meter. Finally, both experimental and computational studies are presented investigating the ultrafast thermal response cycle of nanowires undergoing femtosecond heating.

Gold monolayer-protected nanoclusters (MPCs) with average diameters of 1-5 nm protected by alkane- and arenethiolates were synthesized. Mixed-monolayer protected nanoparticles (MMPCs) were prepared by functionalizing hexanethiolate-protected MPCs with either 11-mercaptoundecanoic acid (MUA-MMPC), 11-mercaptoundecanol (MUO-MMPC), or 4-aminothiophenol (ATP-MMPC) using ligand place exchange. Presentation of various chemical reagents such as nucleophile, acid, or base and change in physical environment through ultrasonic and thermal irradiation resulted in changes to particles and their physical properties. Thermogravimetric analysis (TGA) was used to measure maximum temperature of the derivated thermogravimetric peaks (Tmax,DTG) as a means of comparing temperature dependence of mass loss. The absorption spectrum within the surface plasmon resonance (SPR) band was monitored over time throughout chemical and ultrasonic treatments to assess stability of these particles in solution. MUA-MMPCs and ATP-MMPCs were self-assembled with Cu2+, poly(sodium 4- styrenesufonate), poly(allylamine hydrochloride), generation 2 polyamidoamine dendrimer, and C60 fullerene as linking molecules on functionalized glass substrates using a layer-by-layer approach resulting in nanoparticle multi-layer films. The thin films were characterized using UV-vis spectroscopy during deposition, and then before and after chemical treatment, and thermal and ultrasonic irradiation to assess stability of nanocomposites. Finally, an in-situ cross-linking approach was used to deposit gold MPC-C60 thin film nanocomposite on functionalized glass substrate. UV-vis spectroscopy was used to monitor deposition rates of the resulting film in comparison with the MPC-C60 multilayer film assembled layer-by-layer. These MPC-C60 nanocomposites were also characterized using conductive atomic force microscopy (C-AFM).

This work presents a new form of microscopy, the instrument constructed to demonstrate it, the images produced and the image contrast mechanisms seen for the first time. Some of its future scientific potential is described and finally, recent work towards advancing the method is discussed. Many forms of microscopy exist, each with unique advantages. Of several broad categories that they could be grouped into, those that use particle beams have proven very generally useful for micro and nano-scale imaging, including Scanning Electron, Transmission Electron, and Ion Beam microscopes. These have the disadvantage, however, of implanting electric charges into the sample, and usually at very high energy relative to the binding energy of molecules. For most materials this modifies the sample at a small scale and as we work increasingly towards the nano-scale, this is a serious problem. The Neutral Atom Microscope (NAM) uses a beam of thermal energy (under 70 meV) non-charged atoms or molecules to probe an atomic surface. For several decades scientists have been interested in this possibility, using a focused beam. Scattering of neutral atoms provides a uniquely low-energy, surface-sensitive probe, as is known from molecular beam experiments. We have developed a new approach, operating with the sample at a close working distance from an aperture, the need for optics to focus the beam is obviated. The demonstrated, practical performance of this "Pinhole" NAM exceeds all other attempts by great lengths by many measures. The unique images resulting and contrast mechanism discoveries are described. The future potential for nano-scale resolution is shown.

The contrast mechanism in Kerr imaging is the apparent angle through which the plane of polarization is rotated upon reflection from a magnetic surface. This can be calculated for a well characterized surface given the polarization state of the incident light. As in traditional optical microscopy, the spatial resolution is limited by diffraction to roughly half the wavelength of the illumination light. The diffraction limit can be circumvented through the use of near-field scanning optical microscopy, in which the illumination source is an evanescent field at the tip of a tapered optical fiber. A novel probe design for near-field optical imaging in reflection mode will be proposed, and experimental work on the development of a near-field Kerr microscope performed up to this point will be presented. The complication in merging these two techniques arises from the complex polarization profile of the evanescent field. This profile can be characterized for a given probe geometry with the use of electromagnetic field modeling software, allowing for subsequent modeling of the polarization profile of the optical response. An algorithm for predicting the optical response to a near-field probe tip from a generalized multilayer thin-film is presented.

In the last 50 years, the semiconductor industry has been scaling the silicon transistor to achieve faster devices, lower power consumption, and improve device performance. Transistor gate dimensions have become so small that short channel effects and gate leakage have become a significant problem. To address these issues, performance enhancement techniques such as strained silicon are used to improve mobility, while new high-k gate dielectric materials replace silicon oxide to reduce gate leakage. At some point the fundamental limit of silicon will be reached and the semiconductor industry will need to find an alternate solution. The advent of graphene led to the discovery of other layered materials such as the transition metal dichalcogenides. These materials have a layered structure similar to graphene and therefore possess some of the same qualities, but unlike graphene, these materials possess sizeable bandgaps between 1-2 eV making them useful for digital electronic applications. Since initially discovered, most of the research on these films has been from mechanically exfoliated flakes, which are easily produced due to the weak van der Waals force binding the layers together. For these materials to be considered for use in mainstream semiconductor technology, methods need to be explored to grow these films uniformly over a large area. In this research, atomic layer deposition (ALD) was employed as the growth technique used to produce large area uniform thin films of several different transition metal dichalcogenides. By optimizing the ALD growth parameters, it is possible to grow high quality films a few to several monolayers thick over a large area with good uniformity. This has been demonstrated and verified using several physical analytical tests such as Raman spectroscopy, photoluminescence, x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron spectroscopy, and scanning electron microscopy, which show that these films possess the same qualities as those of the mechanically exfoliated films. Back-gated field effect transistors were created and electrical characterization was performed to determine if ALD grown films possess the same electronic properties as films produced from other methods. The tests revealed that the ALD grown films have high field effect mobility and high current on/off ratios. The WSe2 films also exhibited ambipolar electrical behavior making them a possible candidate for complementary metal-oxide semiconductor (CMOS) technology. Ab-initio density functional theory calculations were performed and compared to experimental properties of MoS2 and WSe2 films, which show that the ALD films grown in this research match theoretical predictions. The transconductance measurements from the WSe2 devices used, matched very well with the theoretical calculations, bridging the gap between experimental data and theoretical predictions. Based upon this research, ALD growth of TMD films proves to be a viable alternative for silicon based digital electronics.

The main objective of this thesis is to perform a study of and optimize the most direct and practical gas mixture composition inside the Radial Time Projection Chamber for the Barely-Offshell Nucleon Structure (BONuS 12) detector for use in the CLAS 12 detector in Experimental Hall B at Thomas Jefferson National Accelerator Facility (JLab). The optimization of these conditions will enhance the performance and resolution of the detector. The original BONuS 6 experiment utilized a gas composition of 80 % He and 20% Dimethyl Ether (DME). With the extensive 12 GeV energy upgrade constructed at JLab and the new BONuS 12 detector established , it is imperative that the gas composition utilized, is best suited to facilitate the experimental needs and demands. BONuS 12 is an experiment designed to measure the momentum of recoiling spectator protons down to 70 MeV/c. This technique will extract the structure function Fn 2 at large x from 0.1 up to 0.8 over a significant range in Q2 and W from the nucleon mass, with a beam energy of 11 GeV, enabling us to essentially select free neutrons.

Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of AlnOm (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al2nO3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al4O4, Al5O3, Al6O4, and Al6O5. The structures of the planar clusters have external Al atoms bound to a single O atom. Their electronic stability can be explained by the multiple valence Al sites with the internal Al atoms having an oxidation state of +3, while the external Al atoms have an oxidation state of +1. The formation of AlnOm+ clusters with high concentrations of oxygen were found experimentally. To determine the stability of such clusters theoretical methods were used to examine the geometric and electronic structure of these clusters (2≤n≤7; 1≤m≤10). The structures were found to be below average in terms stability, implying formation in a low collision environment.

<p>GaN quantum dots grown by molecular beam epitaxy are examined by micro-photoluminescence. The exciton and biexciton emission are identified successfully by power-dependence measurement. With two different samples, it can be deduced that the linewidth of the peaks is narrower in the thicker deposited layer of GaN. The size of the GaN quantum dots is responsible for the binding energy of biexciton (E^b_XX); E^b_XXdecreases with increasing size of GaN quantum dots. Under polarization studies, polar plot shows that emission is strongly linear polarized. In particular, the orientation of polarization vector is not related to any specific crystallography orientation. The polarization splitting of fine-structure is not able to resolve due to limited resolution of the system. The emission peaks can be detected up to 80 K. The curves of transition energy with respect to temperature are S-shaped. Strain effect and screening of electric field account for  blueshift of transition energy, whereas Varshni equation stands for redshifting. Both blueshifting and redshifting are compensated at temperature ranging from 4 K to 40 K.</p>