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An investigation of the problem of inelastic scattering process under the Coulomb Born approximation is given. Different approaches to calculate Coulomb wavefunctions in the momentum space representation are analyzed and a discussion of their existences in the generalized distribution sense is provided. Inokuti’s approach of finding the differential cross section in the momentum space representation under the Coulomb Born approximation is described and a different approach with an application of the Bremsstrahlung integral is developed and compared with Inokuti’s approach.

An investigation of the problem of inelastic scattering process under the Coulomb Born approximation is given. Different approaches to calculate Coulomb wavefunctions in the momentum space representation are analyzed and a discussion of their existences in the generalized distribution sense is provided. Inokuti’s approach of finding the differential cross section in the momentum space representation under the Coulomb Born approximation is described and a different approach with an application of the Bremsstrahlung integral is developed and compared with Inokuti’s approach.

Este trabalho visa o estudo de colisões atômicas mediadas por fótons. Devido à presença da luz ressonante consideramos em nosso sistema os processos de excitação e decaimento atômicos. Em particular, o decaimento atômico tem sua importância no estudo das armadilhas magneto-ópticas, pois este decaimento poder ser um dos fatores que limita a permanência dos átomos confinados neste tipo de armadilha. Apresentaremos uma formulação inédita para a resolução numérica das equações de populações e coerências que descrevem o processo colisional para um par atômico de átomos de dois níveis. Nesta formulação, não utilizamos aproximação, com isso foi possível também, neste trabalho, checarmos a validade da teoria semi-clássica, uma vez que esta é elaborada por um método aproximativo. Comparando nossa formulação, ao qual batizamos de formalismo quântico, com o formalismo semi-clássico, verificamos que a validade deste último restringe-se quando atribuímos determinados valores para o momentum e largura do pacote de ondas, associado à partícula reduzida. Baseado nas redes-ópticas, apresentaremos também um modelo de experimento que possibilite a preparação de um estado inicial para dois átomos colidentes na presença de um feixe laser de prova. Um outro estudo consiste em verificarmos a existência de um potencial efetivo que possibilite descrever o mesmo resultado, assintoticamente, utilizando os formalismos quântico e o Liouvilliano clássico / We study atomic collisions mediated by photons. Due to the presence of remnant light, we consider atomic decay and excitation processes. In particular, the atomic decay is important to the study of magneto-optical traps, because this process is one of the factors limiting the time of atomic confinement in these devices. We present a new formulation to solve numerically the equations describing the populations and coherences involved in the collision process of a pair of two-level atoms. This is a numerically exact approach; hence we have been able to check the semi-classical results. We verify that the validity of this approximation is restricted to certain ranges of momentum and wave-packet width, both associated with the reduced particle. Based on current optical-lattice technology, we also present a thought experiment in which it is possible to prepare an initial state of the two colliding atoms in the presence of a probe laser beam. Another study concerns the verification of the existent of an effective potential which gives the correct asymptotic quantum collision output in a classical Liouvillian framework

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 184-188).

Este trabalho visa o estudo de colisões atômicas mediadas por fótons. Devido à presença da luz ressonante consideramos em nosso sistema os processos de excitação e decaimento atômicos. Em particular, o decaimento atômico tem sua importância no estudo das armadilhas magneto-ópticas, pois este decaimento poder ser um dos fatores que limita a permanência dos átomos confinados neste tipo de armadilha. Apresentaremos uma formulação inédita para a resolução numérica das equações de populações e coerências que descrevem o processo colisional para um par atômico de átomos de dois níveis. Nesta formulação, não utilizamos aproximação, com isso foi possível também, neste trabalho, checarmos a validade da teoria semi-clássica, uma vez que esta é elaborada por um método aproximativo. Comparando nossa formulação, ao qual batizamos de formalismo quântico, com o formalismo semi-clássico, verificamos que a validade deste último restringe-se quando atribuímos determinados valores para o momentum e largura do pacote de ondas, associado à partícula reduzida. Baseado nas redes-ópticas, apresentaremos também um modelo de experimento que possibilite a preparação de um estado inicial para dois átomos colidentes na presença de um feixe laser de prova. Um outro estudo consiste em verificarmos a existência de um potencial efetivo que possibilite descrever o mesmo resultado, assintoticamente, utilizando os formalismos quântico e o Liouvilliano clássico / We study atomic collisions mediated by photons. Due to the presence of remnant light, we consider atomic decay and excitation processes. In particular, the atomic decay is important to the study of magneto-optical traps, because this process is one of the factors limiting the time of atomic confinement in these devices. We present a new formulation to solve numerically the equations describing the populations and coherences involved in the collision process of a pair of two-level atoms. This is a numerically exact approach; hence we have been able to check the semi-classical results. We verify that the validity of this approximation is restricted to certain ranges of momentum and wave-packet width, both associated with the reduced particle. Based on current optical-lattice technology, we also present a thought experiment in which it is possible to prepare an initial state of the two colliding atoms in the presence of a probe laser beam. Another study concerns the verification of the existent of an effective potential which gives the correct asymptotic quantum collision output in a classical Liouvillian framework

Neste trabalho implementamos um programa computacional capaz de descrever passo-a-passo o processo de colisão entre dois átomos confinados numa armadilha magneto-óptica em regime frio. Para isso utilizamos o formalismo de Wigner, que é uma formulação equivalente à mecânica quântica, para encontrar-mos uma aproximação quase-clássica para as equações que descrevem o sistema. Este formalismo permite-nos separar os graus de liberdade externos dos átomos colidentes, que podem ser tratados de maneira quase-clássica, dos graus internos de liberdade, os quais não tem contraparte clássica e, portanto, são tratados quanticamente / In this work we implement a computer program that describes, step by step, the collision process between two atoms confined in a magneto-optical trap in the cold regime. Here we utilize the Wigner-function theory, which is a formulation of quantum mechanics in terms of a phase space, to find a quasi-classical approx¬imation of the dynamical equations that govern the time evolution of the system. This approach allows us to describe the dynamics in terms of external and internal degrees of freedom. The former degrees of freedom are treated quasi-classically, while the latter, because they do not have a classical counterpart, are treated quan¬tum mechanically

[Truncated abstract] This work investigated electron correlation and spin-dependent effects in electron scattering from zinc for incident electron energies from the lowest excitation threshold at 4.003 eV to 50 eV. Experiments were performed using a crossed-beams electron impact spectrometer, which included an unpolarised electron gun, and also a spin-polarised electron gun. The apparatus was tested, and shown to be operating well, by repeating past studies of electron scattering from helium and argon. Emission cross sections for the 4s4p 3P1, 4s4p 1P1, 4s5s 3S1, 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 states were measured from the respective thresholds to 50 eV. These were compared with Convergent Close-Coupling (CCC) and B-spline R-matrix (BSRM) calculations of the 4s4p 3P1, 4s4p 1P1, 4s5s 3S1, 4s4d 1D2 and 4s4d 3D1;2;3 emission cross sections. There are serious discrepancies between the theories, and between the theories and experiment, which indicates strong continuum coupling and innershell excitation effects in the electron excitation of zinc. The differential elastic scattering signal at scattering angles of 30 , 54 , 90 and 110 was measured for incident electron energies from just below the lowest excitation threshold at 4.003 eV, to the ionisation threshold at 9.394 eV. Some assignments given by Sullivan et al [1] and Zatsarinny and Bartschat [2] were confirmed by the present experiment. An area of disagreement in the literature concerning the nature of a feature observed at the 4s4p 1P1 threshold at 5.796 eV was resolved in favour of Zatsarinny and Bartschat, who assign the feature as a cusp. ... Below the ionisation threshold, the 4s4p 3P1 photon excitation function supports the assignment of the near-4s4p 1P1 threshold feature as a cusp. Some of the overlapping negative-ion resonances which were observed near 7.5 eV in the 4s4p 3P1, 4s4p 1P1 and 4s5s 3S1 photon excitation functions were assigned with the assistance of the BSRM calculations of Zatsarinny and Bartschat. However, continuum coupling effects above 8 eV seem to cause the theoretical negative-ion resonance predictions to break down. Above the ionisation threshold, the near-11 eV negative-ion resonance effects depend on the configuration n, L and S of the neutral state excitation observed. This may be due to the properties of the mixed negative ion component states. Postcollision interaction (PCI) effects the 4s5s 3S1, 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 photon excitation functions. The PCI mechanism can populate the 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 states because the scattered and ejected electrons have a similar energy, and can thus exchange a large amount of orbital angular momentum. The present work demonstrates that electron correlation effects, especially those associated with innershell excitation, are very significant in electron scattering from zinc. Existing theoretical models of electron scattering from zinc inadequately treat electron correlations, and as a result of this are inaccurate, as shown here. The studies presented here should guide the development of models that accurately describe the innershell excitation effects, which are important for zinc and a great many other atoms.

Experimental and theoretical investigations of highly-excited molecules are presented that advance the current state of knowledge of intramolecular interactions in highly-excited molecular states. A quantitative analysis of intramolecular interactions in excited hydrogen fluoride is presented, in which the rotational levels of the B singlet-Sigma+, v = 29 vibronic level are shown to mix with the corresponding e-parity components of the C singlet-Pi, v = 0 level. Extrapolating the experimentally-derived mixing parameter to the unperturbed limit reveals an unperturbed value of the aF hyperfine parameter of 4132(25) MHz. Coupling energies between the ion-pair curve and long-range asymptotes of covalent states are calculated for a large number of alkali–alkali collision channels, revealing the dependence on the internuclear distance at which the crossing takes place and forming a foundational step for the calculation of cross-sections and rate coefficients for different charge-exchange and other processes. To advance the experimental investigation of these systems, optical instrumentation and associated control systems have been designed and constructed for cooling and trapping lithium in preparation for experimental studies of cold-collisions that will be informed by, and ultimately a test of, some of these calculated ionic–covalent coupling energies. A novel scheme for systematic optimization of peak-locking has been developed and implemented, providing a rigorous assessment of the optimal experimental parameters. A side-of-filter offset-locking scheme was implemented, characterizing and correcting for a previously unexplained offset in the error-signal. A novel calibrated polarimetry scheme is demonstrated, correcting for the primary sources of uncertainty relating to manufacturing tolerances and experimental errors. The calibrated set of polarization measurements is used to examine the purity of the optical polarization state in the light sources to be used for trapping lithium. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-01-31 11:30:22.479