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This thesis is based on studies of multiple ionization of atoms and molecules induced by the absorption of a single photon. For the experimental investigations a time-of-flight magnetic bottle spectrometer has been used to detect the emitted electrons in coincidence. The method of coincidence time-of-flight spectroscopy and the experimental setup used is described. Experimental and theoretical results on molecular double core holes (DCHs) and multiple ionization of atoms are presented. Molecular DCHs are of considerable interest, as their chemical shifts are predicted to be more sensitive than their single core hole counterparts. Using CH4 and NH3 as examples, it is shown that molecules with two vacancies in the innermost shell can be studied using synchrotron light in combination with our coincidence technique. The chemical shifts of S 2p DCHs are investigated for the molecules CS2, H2S and SO2 and the influence of relaxation effects on the shifts are estimated. In the studies of atoms, the main focus is on the processes leading to double and higher degrees of ionization, and the final state populations. In cadmium double photoionization in the photon energy region 40-200 eV occurs mainly by indirect ionization via valence ionized satellite states and through Coster-Kronig decay of inner shell hole states. In valence-valence ionization of krypton by 88 eV photons both direct and indirect ionization processes are found to be important. For the indirect pathways strong final state selectivity in the autoionization decays of the intermediate states is observed. Triple ionization of krypton via intermediate core-valence doubly ionized states is investigated. The intermediate states are observed in the energy region 120-125 eV, and their decay to states of the triply charged ion is mapped. Experimental and theoretical results on the formation of 2p double hole states in argon are presented. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Providing intense, contamination-free beams of rare isotopes to experiments is a challenging task. At isotope separator on-line facilities such as ISAC at TRIUMF, the choice of production target and ion source are key to the successful beam delivery. Due to their element-selectivity, high efficiency and versatility, resonant ionization laser ion sources (RILIS) gain increasingly in importance. The spectroscopic data available are typically incomplete in the region of excited- and autoionizing atomic states. In order to find the most efficient ionization scheme for a particular element, further spectroscopy is often required. The development of efficient laser resonant ionization schemes for yttrium and astatine is presented in this thesis. For yttrium, two ionization schemes with comparable relative intensities were found. Since for astatine, only two transitions were known, the focus was to provide data on atomic energy levels using resonance ionization spectroscopy. Altogether 41 previously unknown astatine energy levels were found.

The detection of sound sources with microphone arrays can be enhanced through processing individual microphone signals prior to the delay and sum operation. One method in particular, the Phase Transform (PHAT) has demonstrated improvement in sound source location images, especially in reverberant and noisy environments. Recent work proposed a modification to the PHAT transform that allows varying degrees of spectral whitening through a single parameter, andamp;acirc;, which has shown positive improvement in target detection in simulation results. This work focuses on experimental evaluation of the modified SRP-PHAT algorithm. Performance results are computed from actual experimental setup of an 8-element perimeter array with a receiver operating characteristic (ROC) analysis for detecting sound sources. The results verified simulation results of PHAT- andamp;acirc; in improving target detection probabilities. The ROC analysis demonstrated the relationships between various target types (narrowband and broadband), room reverberation levels (high and low) and noise levels (different SNR) with respect to optimal andamp;acirc;. Results from experiment strongly agree with those of simulations on the effect of PHAT in significantly improving detection performance for narrowband and broadband signals especially at low SNR and in the presence of high levels of reverberation.

Providing intense, contamination-free beams of rare isotopes to experiments is a challenging task. At isotope separator on-line facilities such as ISAC at TRIUMF, the choice of production target and ion source are key to the successful beam delivery. Due to their element-selectivity, high efficiency and versatility, resonant ionization laser ion sources (RILIS) gain increasingly in importance. The spectroscopic data available are typically incomplete in the region of excited- and autoionizing atomic states. In order to find the most efficient ionization scheme for a particular element, further spectroscopy is often required. The development of efficient laser resonant ionization schemes for yttrium and astatine is presented in this thesis. For yttrium, two ionization schemes with comparable relative intensities were found. Since for astatine, only two transitions were known, the focus was to provide data on atomic energy levels using resonance ionization spectroscopy. Altogether 41 previously unknown astatine energy levels were found.

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Les atomes de Rydberg constituent des objets idéaux pour l’étude des systèmes physiques en interaction à longue portée. Transposer à ces atomes très excités les techniques habituelles d’imagerie et de piegeage des atomes froids offrirait de nouvelles opportunités pour le domaine de la simulation quantique. Notre approche consiste à utiliser un atome à deux électrons de valence optiquement actifs tel que l’ytterbium. En effet, les transitions optiques du coeur ionique de cet atome ouvrent la voie à de nombreuses perspectives pour la manipulation optique dans l'état de Rydberg. Lorsque l’atome est doublement excité, il peut néanmoins auto-ioniser puisque son énergie se situe au delà de la première limite d’ionisation. La possibilité de s’affranchir totalement de l’autoionisation est une question ouverte.Dans cette thèse, nous présentons en premier lieu les contributions apportées au montage de l’expérience,du refroidissement des atomes d’ytterbium sur la raie d’intercombinaison à l’excitation dans des états de Rydberg. A cause des interactions entre électrons de valence, la spectroscopie de ces états très excités est plus complexe dans l'ytterbium que dans les atomes alcalins. Une étude expérimentale couplée à une analyse par théorie du défaut quantique à plusieurs voies (MQDT) a été réalisée sur diverses séries Rydberg (s, p, d et f). Cette étude, prérequis essentiel, a permis d’améliorer la précision de plus de deux ordres de grandeur sur la spectroscopie des séries étudiées.L’excitation du coeur ionique a ensuite été mise en place sur la transition 6s1/2 → 6p1/2 . Nous avons alors étudié expérimentalement et théoriquement l’excitation du coeur isolé pour des états de Rydberg de grand moment orbital (l = 5 - 9). Cette étude a montré que l'auto-ionisation est dominée par le couplage au continuum de l'état de coeur 5d3/2. Par opposition a l'atome de baryum, pour lequel l'autoionisation chute rapidement avec le moment orbital de l'électron Rydberg, nous avons montré que cette tendance est moins marquée sur l'ytterbium. Grace à cette étude, nous pourrons déterminer les états pour lesquels la manipulation optique par laser est possible. / Rydberg atoms offer an ideal platform for the study of long-range interacting systems.However, usual techniques for imaging and trapping are unavailable in alkali Rydberg atoms. Our approach rely on the use of a two-optically-active-valence-electrons atom such as ytterbium. Ionic core transitions of this atom offer new perspecives for optical manipulation in the Rydberg state. However,questions remain open, especially on the possibilities of avoiding the autoionization, process which occurs when the atom is doubly excited.In this thesis, we report on the construction of the experiment, from the cooling and trapping of theatoms to the excitation in Rydberg states. Because of the interactions between valence electrons, the spectroscopy of these highly excited states is relatively complicated. An experimental study, coupled to a multi-channel quantum defect analysis (MQDT) has been done on the s,p,d and f Rydberg series. This study produced an improvement on the precision of the spectroscopy of this series by more than two orders of magnitude. We then studied the isolated core excitationon the 6s1/2 -> 6p1/2 transition for Rydberg states of large orbital quantum numbers (l=5-9). This study showed that auto-ionisation is mostly due to the coupling to the continuum of the 5d3/2 core state. In opposition to the barium atom, where auto-ionisation drops rapidly with the orbital quantum number, we have shown that ytterbium is less favourable to that extent. Thanks to this study we will be able to determine which states are good candidates for the optical manipulation.

L'interaction des puissantes impulsions laser avec les gaz atomiques et moléculaires entraîne l’émission de flashs exceptionnellement brefs de lumière XUV grâce au processus de génération harmonique d'ordre élevé (GHOE) de la fréquence laser fondamentale. Ce rayonnement ultra-bref, dans la gamme attoseconde (10⁻¹⁸ s), permet des investigations détaillées de la dynamique électronique ultra-rapide dans la matière. Le travail de cette thèse consiste à étudier les délais de photoionisation au voisinage de différents types de résonances, en utilisant la technique Rainbow RABBIT. Il s'agit d'une technique interférométrique à deux couleurs (XUV + IR) qui permet d'accéder au temps nécessaire à l'électron pour s'échapper du potentiel atomique avec une haute résolution. Nous nous intéressons particulièrement à deux cas: i) les résonances auto-ionisantes spectralement étroites (dizaines de meV) et ii) les minima de type Cooper ayant une largeur spectrale de quelques eV. L'effet de ces structures de continuum sur la dynamique d'ionisation correspondante est étudié. / The interaction of intense laser pulses with atomic and molecular gases results in exceptionally short bursts of XUV light, through the process of high-order harmonic generation of the fundamental laser frequency. This ultrashort radiation, in the attosecond (10⁻¹⁸ s) range, allows detailed investigations of ultrafast electron dynamics in matter. The work of this thesis consists in studying the photoionization delays close to different types of resonances, using the Rainbow RABBIT technique. This is a two-color interferometric technique (XUV + IR) that allows access to the time required for the electron to escape the atomic potential with high resolution. We are particularly interested in two cases: i) autoionizing resonances which are spectrally narrow (tens of meV) and ii) Cooper-type minima which have a spectral width of some eV. The effect of these continuum structures on the corresponding ionization dynamics is studied.

A new experimental approach is reported that focuses on photoionization mass spectrometry of primary photofragments. Photodissociation of molecules and radicals is carried out by using a tunable, pulsed dye laser. Nascent photofragments are subsequently photoionized by time-correlated vacuum-ultraviolet (VUV) radiation, so that only single-photon ionization occurs. Several experimental approaches are used in order to optimize pulsed radiation sources in the VUV that are suitable for pump-probe experiments. Laser systems that rely on frequency tripling in suitable non-linear media are used as an intense VUV radiation source of narrow bandwidth and limited tuning range. Monochromatized laser-produced plasma radiation is also used, which provides tunable VUV radiation throughout the entire VUV energy regime (8-25 eV). Ionized photofragments are finally detected by time-of-flight mass spectrometry. This experimental approach is used in order to investigate the following issues: * Absolute photoionization cross sections of atomic and molecular photofragments are derived from photoionization mass spectrometry. This is shown for the photolysis of chlorine dioxide (OClO), chlorine monoxide (ClO) and ozone (O3). The latter species generates O(1D), so that photoionization and autoionization of this excited species was studied for the first time. * Quantum states and quantum state distributions are derived from photoion yields of primary photofragments in order to characterize photodissociation processes. This is shown for the predissociation of OClO, which yields vibrationally excited ClO in its electronic ground state. * Branching ratios and quantum yields of competing photochemical pathways are determined from photoionization mass spectrometry. The accuracy of this approach is superior to other techniques. These investigations allowed us to investigate photolysis processes of molecules and radicals that are of significant importance with respect to recent issues of atmospherical photoprocesses, such as polar ozone depletion.

Doctor of Philosophy / Department of Physics / Zenghu Chang / The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.