Neutrino physics has been going through rapid developments since the particle was first proposed by Pauli. The observation of neutrino oscillations has prompted an investigation of the issue of neutrino mass, with the "seesaw" mechanism garnering theoretical support. The HUNTER (Heavy Unseen Neutrinos from the Total Energy-momentum Reconstruction) experiment brings together AMO, nuclear physics and high energy physics researchers from Temple University, Houston University, UCLA and Princeton University to develop an apparatus capable of probing the keV-mass range of sterile neutrinos with high precision. The HUNTER detector makes use of the well-established COLTRIMS techniques for the collection of all the decay products of a neutrino-producing decay, and the reconstruction of their initial momenta and energies. Energy and momentum conservation allow then for the reconstruction of the missing neutrino mass.Electrons produced in the decay are guided towards their detector by an optimized set of electrodes paired to a magnetic field to confine their trajectories into spirals. A magnetic shield protects the electron from external stray fields that could alter their trajectories. A thorough study on the main source of background, namely the source scattering of ions, was conducted. As an additional topic, the feasibility of a directional-sensitive dark matter search experiment has been studied. Simple models of galactic dark matter distribution suggest that the motion of the Earth in space might introduce a directional anisotropy in the WIMPs momentum distribution at the Earth. The shape of a WIMP-like recoil in a target material could be be used to extract directional information for the incident WIMP, and thus confirm the anisotropy. The peculiar microphysics of liquid Argon requires thermalization of ionization electrons for a signal to form. To determine if directional information can be extracted, one needs to understand the energy spectrum of the electrons emitted in recoil event. Then, one needs a model to determine the time scale of the thermalization, and the distance to which the electrons travel. / Physics

Doctor of Philosophy / Department of Physics / Itzhak Ben-Itzhak and Charles Lewis Cocke / A commercially available modern laser can emit over 10^15 photons within a time window of a few tens of femtoseconds (10^-15 second), which can be focused into a spot size of about 10 um, resulting in a peak intensity above 10^14 W/cm^2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10^-18 second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source implemented in this work is a single harmonic in the VUV regime (around 15 eV) filtered out from a monochromator. Experiments on D_2 molecules have been conducted using the 9th or the 11th harmonic as the pump pulse. Novel dissociative ionization pathways via highly excited states of D_2 have been revealed, thus suggesting potential applications for time-resolved studies and control of photochemistry processes.

La dynamique de fragmentation des molécules poly-atomiques est un problème compliqué du fait de l'existence de couplages entre leurs différents degrés de liberté. Dans le but de comprendre le rôle de ces couplages, nous avons étudié la fragmentation de molécules triatomiques induite par impact d'ions rapides multichargés. L'intérêt de ces ions est de conduire à une ionisation multiple de la molécule au cours d'une interaction d'une durée de quelques attosecondes (10-18s). Ce temps est suffisamment bref pour que la relaxation, par fragmentation, de l'ion moléculaire ainsi créé se fasse hors de toute perturbation extérieure. Les premières études réalisées sur le CO2 soumis aux ions Ni24+ de 8 MeV/u ont montré que la fragmentation de l'ion moléculaire CO2q+ pouvait être modélisée par une fragmentation concertée synchrone (q=3) ou une fragmentation concertée asynchrone (q=2), i.e. par l'intermédiaire d'un mode de vibration asymétrique de la molécule. Nous avons réalisé des expériences avec des molécules non linéaires telles que NO2, D2O, H2O et HDO pour lesquelles les couplages entre degrés de liberté sont différents de ceux rencontrés dans les molécules linéaires comme CO2, et ainsi tester ce modèle de dissociation plus sévèrement. Dans le cas de fragmentation du NO22+ induite par des ions Ne8+ de 4.7Mev/u, des fortes différences, par rapport à CO22+, ont été observées en raison de la contribution de la géométrie. La fragmentation de HDO2+ a permis de confirmer à haute et basse énergie de collision, un important effet isotopique: la rupture de la liaison O-H est 5.7 fois plus probable que celle de la liaison O-D.

Doctor of Philosophy / Department of Physics / B.D. DePaola / In recent years, coherent excitation techniques have focused on the ability to efficiently prepare atomic or molecular systems into a selected state. Such population control plays a key role in cutting-edge research taking place today, such as in the areas of quantum information and laser-controlled chemical reactions. Stimulated Raman adiabatic passage (STIRAP) is a widely-used coherent excitation technique that provides a relatively robust control mechanism for efficiently exciting a target population into a desired state. While the technique is well proven, current experimental techniques yield little information on the population dynamics taking place throughout the excitation process, and experimentalists rely solely on final excited-state measurements to determine the efficiency of population transfer. This dissertation presents a unique diagnostic tool to measure multilevel coherent population transfer on a short (nanosecond) timescale. The technique described here uses magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) as a noninvasive probe of a coherently-controlled system. It provides extremely detailed information about the excitation process, and highlights some important characteristics seen in excited populations that would otherwise be misleading or completely overlooked if one were to use more traditional diagnostic techniques. This dissertation discusses both the theoretical and experimental results applied to three-level coherently excited target populations of Rb-87.

A partir des années 1990, la spectroscopie d'impulsion d'ions de recul s'est imposée comme l'outil idéal pour l'étude des collisions ion-atome et ion -molécule. Le développement de cette technique expérimentale au cours des vingt dernières années est ici détaillé et illustré par des résultats marquants obtenus dans ce domaine au GANIL (CAEN) et au J.R. MacDonald Laboratory (Kansas State University). La spectroscopie d'impulsion d'ions de recul se trouve être également particulièrement bien adaptée à la mesure du paramètre de corrélation angulaire b-v en décroissance b L'expérience LPCTrap, installée au GANIL, est basée sur l'utilisation de cette technique et d'un piège de Paul pour le confinement des noyaux radioactifs. Les mesures précises qui ont été réalisées permettent à la fois de tester certaines hypothèses essentielles du Modèle Standard des particules élémentaires et d'étudier le processus d'ionisation par " shakeoff " de l'électron.