Philosophiae Doctor - PhD / In the first experiment high spin states in 194Tl, excited through the 181Ta (18O, 5n) heavyion fusion evaporation reaction were studied using the AFRODITE array at iThemba LABS. The γ-γ coincidences, RAD ratios and linear polarization measurements were carried out and the previously known level scheme of 194Tl was significantly extended. A total of five rotational bands four of which are new were observed. A pair of rotational bands associated with the πh9/2 ⊗ νi−1 13/2 configuration at lower spins and with the πh9/2 ⊗ νi−3 13/2 configuration at higher spins was found and interpreted as the first possible chiral bands followed above the band crossing. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. In the second experiment lifetimes in 194Tl were measured using the DSAM technique with the excited states in this nucleus populated through the 181Ta (18O, 5n) reaction. A total of 25 lifetimes and 30 reduced transition probabilities of magnetic dipole B(M1) and electric quadrupole B(E2) have been evaluated. Furthermore B(M1) and B(E2) reduced transition probabilities in Bands 1 and 4, which have been regarded as chiral candidates, were found to be close to each other and reveals strong splitting along spin values. This further supports the proposed chiral nature of these two bands.

Une onde électromagnétique est définie par son amplitude, son vecteur d'onde, sa fréquence et son moment angulaire. Ce dernier peut être séparé en deux parties : la polarisation (associée au moment angulaire de spin), et le moment angulaire orbital. Ce dernier n'a vraiment été étudié qu'à partir de ces dernières années. Cette thèse a pour but d'approfondir les connaissances sur ce moment angulaire orbital. Des prototypes ont ainsi été réalisés, et des outils d'analyse ont été développés. Dans un premier temps, une étude du transfert de ce moment angulaire orbital à un objet macroscopique, à la fréquence de 870 MHz, est présentée. Une interprétation du mécanisme de transfert est ensuite proposée, supportée par le calcul des équations de champs et des simulations électromagnétiques. Dans un second temps, la conception et la réalisation de deux antennes, pouvant générer une onde possédant un moment angulaire orbital, sont présentées. Ces deux antennes utilisent une lame de phase avec une loi à dépendance angulaire. La première est une lame de phase dite « spirale », à permittivité constante et à hauteur variable. La seconde est une lame à gradient d'indice, à permittivité variable et à hauteur constante. Ces deux antennes ont été simulées, puis mesurées au sein de la chambre anéchoïque CHEOPS (DGA-MI, Bruz). Des cartographies sur un plan du champ ont ainsi été obtenues. Dans un dernier temps, la réflexion sur des surfaces courbes et planes, et l'influence de l'échantillonnage sur l'estimation des modes d'OAM, ont été étudiées. En ce qui concerne la réflexion, les résultats de simulations sont prometteurs, et semblent indiquer l'existence d'une relation entre les déformations du faisceau réfléchi et le type de surface. Pour l'estimation des modes d'OAM, les valeurs de champs sont extraites sur un cercle. Différents paramètres (positionnement et rayon du cercle) ont été considérés, et une méthode d'estimation des modes d'OAM sur une large bande de fréquence est proposée. / An electromagnetic wave is defined by its amplitude, its wave vector, its frequency and its angular momentum. This momentum can be decomposed into two components: polarization (associated to spin angular momentum), and orbital angular momentum. The later has not been investigated thoroughly until the last few years. To deepen the knowledge on orbital angular momentum, both prototypes and analysis tools have been developed in this thesis. First, study of orbital angular momentum transfer to a macroscopic object, at a frequency of 870 MHz, is presented. An interpretation of the transfer mechanism is then proposed, supported by the calculation of field equations and electromagnetic simulations. Secondly, the conception and the realization of two antennas able to generate an EM wave with orbital angular momentum are presented. These antennas use phase plates with an angular dependent law. The first one is a “spiral” phase plate, with constant permittivity and variable height. The second one has variable permittivity and constant height. Both have been simulated and characterized in CHEOPS anechoic chamber (DGA-MI, Bruz). Measurements of magnitude and phase, on a plane, have been obtained. Lastly, total reflection on planar and curved surfaces and influence of sampling on OAM modes estimation were investigated. Simulation results of reflected waves are promising and show a relationship between the induced deformations and the object reflected on. As for OAM modes estimation, study has been performed using an extraction circle on the wave front. Several parameters (center of the circle, radius) have been considered, and a method for OAM modes estimation on a large bandwidth is proposed.

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The three-body bound state problem is considered using configuration-space Faddeev equations within the framework of the total-angular-momentum representation. Different three-body systems are considered, the main concern of the investigation being the i) calculation of binding energies for weakly bounded trimers, ii) handling of systems with a plethora of states, iii) importance of three-body forces in trimers, and iv) the development of a numerical technique for reliably handling three-dimensional integrodifferential equations. In this respect we considered the three-body nuclear problem, the 4He trimer, and the Ozone (16 0 3 3) system. In practice, we solve the three-dimensional equations using the orthogonal collocation method with triquintic Hermite splines. The resulting eigenvalue equation is handled using the explicitly Restarted Arnoldi Method in conjunction with the Chebyshev polynomials to improve convergence. To further facilitate convergence, the grid knots are distributed quadratically, such that there are more grid points in regions where the potential is stronger. The so-called tensor-trick technique is also employed to handle the large matrices involved. The computation of the many and dense states for the Ozone case is best implemented using the global minimization program PANMIN based on the well known MERLIN optimization program. Stable results comparable to those of other methods were obtained for both nucleonic and molecular systems considered. / Physics / D.Phil. (Physics)

Electromagnetic processes induced by electron scattering off few-nucleon systems are theoretically investigated in the non-relativistic formalism. Non-relativistic one-body nuclear current operators are used with a parametrization of nucleon electromagnetic form factors based on recent experimental nucleon scattering data. Electromagnetic form factors of three-nucleon and four-nucleon systems are calculated from elastic electron-nucleus scattering information. Nuclear response functions used in the determination of differential cross sections for inclusive and exclusive quasi-elastic electron-nucleon scattering from the 4He nucleus are also calculated. Final-state interactions in the quasi-elastic nucleon knockout process are explicitly taken into account using the Glauber approximation. The sensitivity of the response functions to the final-state interactions is investigated. The Antisymmetrized Molecular Dynamics approach with angular momentum and parity projection is employed to construct ground state wave functions for the nuclei. A reduced form of the realistic Argonne V18 nucleon-nucleon potential is used to describe nuclear Hamiltonian. A convenient numerical technique of approximating expectation values of nuclear Hamiltonian operators is employed. The constructed wave functions are used to calculate ground-state energies, root-mean-square radii and magnetic dipole moments of selected light nuclei. The theoretical predictions of the nuclear properties for the selected nuclei give a satisfactory description of experimental values. The Glauber approximation is combined with the Antisymmetrized Molecular Dynamics to generate wave functions for scattering states in quasi-elastic scattering processes. The wave functions are then used to study proton knockout reactions in the 4He nucleus. The theoretical predictions of the model reproduce experimental observation quite well. / Physics / Ph D. (Physics)

New dynamical applications of quantum beat spectroscopy (QBS) to molecular dynamics are employed to probe the angular momentum polarization effects in photodissociation and molecular collisions. The magnitude and the dynamical behaviour of angular momentum alignment and orientation, two types of polarization, can be measured via QBS technique on a shot-by-shot basis. The first part of this thesis describes the experimental studies of collisional angular momentum depolarization for the electronically excited state radicals in the presence of the collider partners. Depolarization accompanies both inelastic collisions, giving rise to rotational energy transfer (RET), and elastic collisions. Experimental results also have a fairly good agreement with the results of quasi-classical trajectory scattering calculations. Chapter 1 provides the brief theories about the application of the QBS technique and collisional depolarization. Chapter 2 describes the method and instrumentation employed in the experiments of this work. In Chapter 3, the QBS technique is used to measure the total elastic plus elastic depolarization rate constants under thermal conditions for NO(A,v=0) in the presence of He, Ar, N2, and O2. In the case of NO(A) with Ar, and particularly with He, collisional depolarization is significantly smaller than RET, reflecting the weak long-range forces in these systems. In the case of NO(A)+N2/O2, collisional depolarization and RET are comparable, reflecting the relatively strong long-range forces in these systems. In Chapter 4, the QBS technique is used to measure the elastic and inelastic depolarization and total RET rate constants for OH(A,v=0) under thermal conditions in the presence of He and Ar, as well as the total depolarization rate constants under superthermal conditions. In the case of OH(A)+He, elastic depolarization is sensitive to the N rotational state, and inelastic depolarization is strongly dependent on the collision energy. In the case of OH(A)+Ar, elastic depolarization is insensitive to N, and inelastic depolarization is less sensitive to the collision energy, reflecting that the relatively strong long-range force in OH(A)+Ar system. The second part of this thesis describes the experimental studies of photodissociation under thermal conditions. Chapter 5 provides a brief introduction about several polarization parameter formalisms used for photodissociation, and the incorporation of the QBS technique to measure these polarization parameters. In this thesis, most polarization parameters of the molecular photofragments are measured using the LIF method, and the QBS technique is used as a complementary tool to probe these polarization parameters. In Chapter 6, rotational orientation in the OH(X,v=0) photofragments from H2O2 photodissociation using circularly polarized light at 193 nm is observed. Although H2O2 can be excited to both the A and B electronic states by 193 nm, the observed orientation is only related to the A state dynamics. A proposed mechanism about the coupling between a polarized photon and the H2O2 parent rotation is simulated, and the good agreement between the experimental and simulation results further confirms the validity of this mechanism. In Chapter 7, rotational orientation in the NO(X,v) photofragments from NO2 photodissociation using circularly polarized light at 306 nm (v=0,1,2) and at 355 nm (v=0,1) is observed. Two possible mechanisms, the parent molecular rotation and the coherent effect between multiple electronic states, are discussed. NOCl is photodissociated using circularly polarized light at 306 nm, and NO(X,v) rotational distributions (v=0,1) and rotational orientation (v=0) are measured. For the case of NOCl, the generation of orientation is attributed to the coherent effect.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); 21 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56768" Urban, Jeffry Todd. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 12/21/2004. Report is also available in paper and microfiche from NTIS.

In this doctoral thesis we investigate several experiments exploring the light orbital angular momentum and the Fraunhofer diffraction of light. Our investigations goes from coherent propagation, continue through incoherent propagation, arriving at semiclassical states used to explore one fundamental problem in quantum mechanics, i. e., the Born’s rule. Therefore, concerning coherent propagation of light with orbital angular momentum, we were first involved with studies about Fraunhofer diffraction of this type of light, by a single slit and by a square aperture. In the former work we studied the Fraunhofer diffraction when the slit center is aligned with the vortex center and when it is out of the vortex center. Concerning the work related to the square aperture, we show that the diffraction by such aperture is not sufficient to characterize the topological charge. Continuing the works, we also investigate the Fraunhofer diffraction of light with orbital angular momentum of fractional topological charge in the real space. An interesting phenomenon, the birth of a vortex, was studied at Fraunhofer plane, showing new conclusions in the study of fractional topological charges. Our studies continued with the Fraunhofer propagation of vortices in incoherent light, unveiling strong correlations between incoherent vortices. Finally, we explored semiclassical aspects of light with orbital angular momentum. Firstly, the topological charge determination via the spatial probability distribution of detection of photons diffracted by a triangular aperture. After, the validation of the Born’s rule using diffraction, by three slits disposed in a triangular configuration, of photons with an extra phase, i. e., the azimuthal phase added to the path phase. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Nesta tese de doutorado investigamos diversos experimentos que exploram o momento angular orbital da luz e a difração de Fraunhofer. Nossas investigações abrangeram desde propagação coerente, passando por propagação incoerente, chegando a estados semiclássicos usados para explorar uma questão fundamental da mecânica quântica, a saber, a regra de Born. Portanto, no que concerne à propagação de luz coerente com momento angular orbital, estivemos envolvidos primeiramente com estudos da difração de Fraunhofer deste tipo de luz, por uma fenda simples e por uma abertura quadrada. No primeiro trabalho estudamos a difração de Fraunhofer quando o centro da fenda está alinhado com o centro do vórtice e quando está deslocado do centro do vórtice. Quanto ao trabalho relacionado à abertura quadrada, mostramos que a difração de Fraunhofer por tal abertura não permite caracterizar a carga topológica. Prosseguindo os trabalhos, investigamos também a difração no plano de Fraunhofer de luz com momento angular de carga fracionária no plano real. Um interessante fenômeno, o nascimento de um vórtice, foi estudado no plano de Fraunhofer, mostrando novas conclusões nos estudos relacionados à carga fracionária. Nossos estudos continuaram com a propagação de Fraunhofer de vórtices em luz incoerente, revelando fortes correlações entre vórtices incoerentes. Por fim, exploramos aspectos semiclássicos da luz com momento angular orbital. Primeiramente, a determinação da carga topológica via distribuição de probabilidade espacial de detecção de fótons difratados por uma abertura triangular. Posteriormente, a validação da regra de Born utilizando difração, por três fendas simples dispostas na forma triangular, de fótons com uma fase extra, ou seja, a fase azimutal, adicionada à fase de caminho.