This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within both organic and inorganic semiconductors. Photoluminescent polymers, highly conducting polymers and nanoscale inorganic semiconductors have been investigated using state-of-the-art ultrafast optical techniques, to provide information on the sub-picosecond photoexcitation dynamics in these systems. The influence of dimensionality on the excitation transfer dynamics in a conjugated polymer blend is studied. Using time-resolved photoluminescence spectroscopy, the transfer transients both for a three-dimensional blend film, and for quasi-two-dimensional monolayers formed through intercalation of the polymer blend between the crystal planes of a SnS2 matrix have been measured. A comparison of the experimental data with a simple, dimensionality-dependent model is presented, based on point dipole electronic coupling between electronic transition moments. Within this approximation, the energy transfer dynamics are found to adopt a three-dimensional character in the solid film, and a two-dimensional nature in the monolayers present in the SnS2 -polymer nanocomposite. The time-resolved conductivity of isolated GaAs nanowires has been investigated by optical-pump terahertz-probe time-domain spectroscopy. The electronic response exhibits a pronounced surface plasmon mode that forms within 300 fs, before decaying within 10 ps as a result of charge trapping at the nanowire surface. The mobility has been extracted using the Drude model for a plasmon and is found to be remarkably high, being roughly one third of that typical for bulk GaAs at room-temperature and indicating the high quality and low bulk defect density in the nanowires studied. Finally, the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers, P3HT and MDMO-PPV, blended with PCBM are presented. The observed terahertz-frequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the π−π* absorption peak (560 nm for P3HT), and significantly below it (800 nm). The photoconductivity at 800 nm is unexpectedly high, which is attributed to the presence of a charge transfer complex. In addition, the excitation-fluence dependence of the photoconductivity is studied over more than four orders of magnitude. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that long-lived positive polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times (~ ps) the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least ~0.1cm2 V−1 s−1. At later times, a sub-linear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer timescale (> 1 μs).

This thesis describes the development and application of condensed-phase cavity-based spectroscopic techniques - namely cavity ring-down spectroscopy (CRDS); cavity enhanced absorption spectroscopy (CEAS); broadband cavity enhanced absorption spectroscopy (BBCEAS) and evanescent wave (EW) variants of all three. The recently-developed cavity technique of EW-broadband cavity enhanced absorption spectroscopy (EW-BBCEAS) has been used—in combination with a supercontinuum source (SC) and a sensitive, fast readout CCD detector—to record of the full visible spectrum (400–700 nm) of a silica-liquid interfacial layer (with an effective thickness ca. 1 µm), at rapid acquisition rates (> 600 Hz) that are sufficient to follow fast kinetics in the condensed phase, in real time. The sensitivity achieved (A_min= 3.9 x 10^-5) is comparable with previous EW-CRDS and EW-CEAS studies, but the spectral region accessed in this broadband variant is much larger. The study of liquid|air interfaces using EW cavity-based techniques is also illustrated for the first time. The first application of BBCEAS to the analysis of microfluidic samples, flowing through a microfluidic chip, is illustrated. Proof-of-principle experiments are presented, demonstrating the technique’s ability to provide full visible broadband spectral measurements of flowing microfluidic droplets, with both high detection sensitivity (α_min < 10^-2 cm^-1) and excellent spatial and temporal resolution: an SC light source and sensitive, fast readout CCD allowed measurement repetition rates of 273 Hz, whilst probing a very small sample volume (ca. 90 nL). A significant portion of this thesis is devoted to demonstrating the powerful capabilities of CEAS, CRDS and BBCEAS in monitoring radical recombination reactions and associated magnetic field effects (MFEs) in solution. The efficacy of CEAS as a high-sensitivity MFE detection method has been established in a proof-of-principle study, using narrow band CEAS in combination with phase-sensitive detection: MFE-induced absorbance changes of ca. 10^-6 could be detected using the modulated CEAS technique and the data are shown to be superior to those obtained using conventional transient absorption (TA) methods typically employed for MFE measurements. The powerful capabilities of CRDS in monitoring radical recombination reactions and associated MFEs are also demonstrated. In particular, a pump-probe CRDS variant allows not only high sensitivity (A_min on the order 10^-6), but also sub-microsecond time-resolution. Combined, these features represent significant advantages over TA. Finally, SC-BBCEAS is used to measure full visible spectra of photoinduced reactions and their MFEs. The applicability of this approach to in vitro MFE studies of Drosophila cryptochrome is demonstrated—the results mark the first in vitro observation of a magnetic field response in an animal cryptochrome, a key result supporting the hypothesis that cryptochromes are involved in the magnetic sense in animals.

Photofragment velocity-map imaging (VMI) has generally been employed to investigate the photodissociation dynamics of relatively small molecular systems (< 5 atoms). The work reported in this thesis focuses on the application of this technique for the investigation of the unimolecular photodissociation of larger chemical systems, which are of interest to a broad cross section of the chemical community. Typically, VMI studies involve state-selective detection of one particular fragmentation product, and so are often limited to the investigation of a single dissociation channel. By employing vacuum ultra-violet (VUV) photoionization, we are able to detect most, if not all of the fragments resulting from the dissociation of a neutral species, with ‘universal’ ionization being achieved in the ideal case when the fragment ionization energies are all lower than the VUV photon energy. This capability becomes particularly important when investigating larger systems, since these often display complex dynamics with multiple competing fragmentation pathways. Our approach allows us to investigate the different photofragmentation processes occurring for a particular system, to evaluate the relative importance of the active dissociation channels, and to gain insight into the energy partitioning amongst the fragments. A study of the UV photodissociation of two neutral alkyl iodide molecules demonstrates the first use in our laboratory of ‘universal’ ionization in combination with VMI. Studies into the photofragmentation processes resulting from 193 nm photoexcitation of neutral N,N-dimethylformamide, a small-molecule model for a peptide bond, and a number of neutral cyclic alkenes, which undergo the retro-Diels-Alder reaction, are also presented. The remaining studies presented in this thesis have investigated the photofragmentation processes of ionic species, generated by means of VUV photoionization. In the case of ion dissociation each fragmentation channel necessarily produces one charged species, which may be detected using the VMI technique. Therefore, such studies provide an insight into all of the active channels. An in-depth VMI study of the UV photodissociation of two ethyl halide cations is presented, which demonstrates the successful investigation of the multiple photofragmentation pathways of these ionic species. The remainder of the cation photodissociation studies are of relevance to a number of common processes known to occur in mass spectrometry, including the McLafferty rearrangement, the retro-Diels-Alder reaction, and ‘peptide’ bond fragmentation. By velocity-map imaging the products of these reactions, further information is obtained concerning these dissociation processes, which are no doubt of interest to the wider chemical community. This work forms part of the velocity-map imaging mass spectrometry (VMImMS) project. VMImMS involves imaging each of the fragmentation products that result from dissociation of a parent molecule of interest, with the aim of increasing the amount of information that can be obtained from a mass-spectrometry-type experiment. The work presented in this thesis demonstrates that VMImMS allows us to unravel details of the dissociation dynamics of both neutral and ionic species, and is potentially a powerful technique for investigating the fragmentation processes of increasingly complex systems.

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.

This thesis describes the combination of two sources of cold atomic or molecular species which can be used to study a wide range of ion-molecule reactions. The challenges in forming these species and in determining the fate of reactive events are explored throughout. Reactions occur in a volume within a radio-frequency ion trap, in which ions have previously been cooled to sub-Kelvin temperatures. Ions are laser-cooled, with migration of ions slowed sufficiently to form a quasi-crystalline spheroidal structure, deemed a Coulomb crystal. Fluorescence emitted as a consequence of laser-cooling is detected; the subsequent fluorescence profiles are used to determine the number of ions in the crystal and, in combination with complementary simulations, the temperature of these ions. Motion imparted by trapping fields can be substantial and simulations are required to accurately determine collision energies. A beam of decelerated molecules is aimed at this stationary ion target. An ammonia seeded molecular beam enters a Stark decelerator, based on the original design of Meijer and co-workers. The decelerator uses time-varying electric fields to remove kinetic energy from the molecules, which exit at speeds down to 35 m/s. A fast-opening shutter and focussing elements are subsequently used to maximise the decelerated flux in the reaction volume while minimising undecelerated molecule transmission. Substantial fluxes of decelerated ammonia are obtained with narrow velocity distributions to provide a suitable source of reactant molecules. Combination of these two techniques permits studies of reactions between atomic ions and decelerated molecules that can be entirely state-specific. Changes in the Coulomb crystal fluorescence profile denote changes in the ion identities, the rate of these changes can be used to obtain rate constants. Determination of rate constants is even possible despite the fact that neither reactant nor product ions are directly observed. This work has studied reactions between sympathetically cooled Xe⁺ ions and guided ND3 and has obtained data consistent with prior studies. Determination of reactive events is complicated if ion identities can change without affecting the fluorescence profile, or if multiple reaction channels are possible. A range of spectroscopic techniques are discussed and considered in regards to determining rate constants and product identities. Pulsed axial excitation of trapped ions can follow rapid changes in average ion weights and subtle changes for small crystals. Time-of-flight mass spectrometry is also demonstrated using the trapping electrodes and is suitable for discrimination of ions formed within the trap.

Cette thèse présente une étude expérimentale et théorique de petites chaines peptidiques modèles en phase gazeuse. Le premier objectif de ce travail consistait à déterminer les conformations préférentiellement adoptées par ces molécules isolées, en vue d’obtenir des informations sur les interactions intra- et inter-moléculaires intervenant dans ces systèmes flexibles. La stratégie expérimentale utilisée associait la vaporisation laser à une détente supersonique et reposait sur la spectroscopie laser de double résonance IR-UV. L’attribution finale des structures a ensuite été réalisée par comparaison des spectres expérimentaux à des spectres issus de calculs de chimie quantique au niveau DFT-D. Dans un deuxième temps, il s’agissait d’étudier la dynamique de relaxation électronique de ces systèmes par spectroscopie pompe-sonde et mesures de fluorescence, et en particulier la dépendance de celle-ci avec la structure secondaire des peptides modèles. La question de la population conformationnelle de molécules flexibles en phase gazeuse est un sujet délicat et bien souvent éludée car les distributions observées expérimentalement résultent d’un passage hors équilibre lors de la détente supersonique, définissant ainsi une température conformationnelle effective. Un modèle statistique a été développé, décrivant le refroidissement et les isomérisations subis durant la détente par une molécule. Les résultats de ces modélisations reproduisent les tendances d’évolution des rapports d’abondances entre conformations observés expérimentalement et permettent de fournir des ordres de grandeurs relatifs aux processus mis en jeu (nombre de collisions efficaces, trajectoire dans la détente après désorption, températures finales) ainsi qu’une meilleure compréhension des processus de refroidissement et de relaxation conformationnelle. Les études conformationnelles ont été appliquées à deux systèmes modèles choisis pour étudier des interactions structurantes intervenant dans les protéines : les interactions protéines-solvant et les interactions hydrophobes. L’étude des complexes (Ac­Phe­NH₂ : H₂O) et (Ac­Phe­NHMe : H₂O) ont permis d’identifier les sites de solvatation préférentiellement occupés par une molécule d’eau et ainsi de proposer des mécanismes de formation des complexes dans la détente supersonique. Le rôle structurant très fort des interactions hydrophobes entre chaînes latérales aromatiques a pu être mis en évidence en étudiant deux peptides modèles contenant un enchainement de plusieurs acides aminés phénylalanine : Ac­Phe­Phe­NH₂ et Ac­Phe­Phe­Phe­NH₂. L’étude des dynamiques de relaxation du premier état excité ππ*, réalisée sur divers peptides modèles, a permis de démontrer la présence d’effets conformationnels importants. Des calculs de chimie quantique (TDDFT et CC2) réalisés sur les systèmes Ac-Phe NH₂ et Ac-Phe NHMe ont montré que cet effet pouvait être expliqué par un transfert d’excitation depuis le cycle aromatique présent sur la chaîne latérale vers les liaisons peptidiques de la chaine principale. Enfin, l’ajout d’une molécule d’eau sur le peptide Ac-Phe NH₂ semble ouvrir de nouvelles voies ultrarapides de relaxation non-radiative. / The very good spectral resolution of laser spectroscopy achieved in the gas phase is a powerful tool to study the folding properties and the hydrogen bonding network of flexible molecules such as small peptide chains. The experimental strategy used in this work to determine the structural properties of these systems is based on IR-UV double resonance spectroscopy and combines laser vaporisation with a supersonic expansion. The final assignment then requires a comparison between experimental spectra and DFT-D calculations. The conformational selectivity brought by gas phase laser spectroscopy also makes it possible to study the dependence of the dynamics of relaxation of electronic excited states of model peptides with their secondary structure by using pump-probe methods or fluorescence detection. The issue of the conformational population of flexible molecules cooled in a supersonic expansion is a difficult issue, often disregarded due to the nonequilibrium processes that control the distributions experimentally observed. A statistical model was developed in order to describe this collisional cooling and the isomerizations experienced by one molecule during the expansion. These calculations were consistent with the experimental trends in the population ratios between conformations, they have provided orders of magnitude for the different processes involved (number of collision, trajectory in the expansion after desorption, final temperatures) and a better understanding of the cooling processes and the conformational relaxation. The conformational studies have been applied to two model systems selected to investigate structural interactions involved in proteins: protein-solvent interactions and hydrophobic interactions. The microhydrated protected phenylalanines (Ac­Phe­NH₂ : H₂O) and (Ac­Phe­NHMe : H₂O) were used to locate the solvation sites preferentially occupied by a water molecule, which then helped to propose a mechanism for the formation of hydrates in the supersonic expansion. The strong structuring properties of hydrophobic interactions between aromatic side chains has been revealed by studying two model peptides containing a sequence of phenylalanine amino acids: Ac­Phe­Phe­NH₂ and Ac­Phe­Phe­Phe­NH₂. A comparative study of the relaxation dynamics of the first ππ* excited state performed on various model peptides has demonstrated the existence of a strong conformational effect. TDDFT and CC2 calculations carried out on the protected phenylalanines have shown that this effect could be explained by an excitation transfer from the aromatic ring of a side chain toward a peptide bond of the backbone. Finally, adding a water molecule to the protected phenylalanine is also found to open new ultrafast channels of nonradiative deactivation.

Cette thèse a été effectuée dans le cadre d'un projet qui vise à explorer les facteurs limitants des performances d'une horloge à ions dans le domaine des fréquences micro-onde. Ce travail repose sur l'observation et la manipulation d'un grand nuage d'ions dans des potentiels de géométries différentes. Le but est l'analyse et le transport d'un grand nuage pouvant dépasser 10^6 ions dans un piège radio-fréquence linéaire à plusieurs zones. Notre groupe à construit un piège à trois zones destiné au piégeage d'ions calcium: deux parties quadrupolaires et une partie octupolaire montées en ligne. Les ions sont créés dans la première partie quadrupolaire et refroidis par laser le long de l'axe du piège. Nous avons d'abord étudié la création d'un grand nuage. La limite actuelle des paramètres du système permet de confiner et détecter des nuages de taille maximale 1,2.10^5 ions. Ensuite, grâce à un protocole de transport rapide et optimisé, ces ions sont transportés dans le deuxième et troisième piège avec une efficacité pouvant atteindre 100%. Les résultats en fonction de la durée de transport montrent une asymétrie entre les deux sens de transport que nous exploitons pour ajouter des ions dans le deuxième piège sans perte du nuage initialement présent. Cette technique d'accumulation a permis de piégér 2,5.10^5 ions dans le deuxième et troisième piège. Ce nombre semble limité par les refroidissement. Enfin, dans l'octupole, les observations montrent que, contrairement aux structures creuses attendues par les modèles, les ions froids s'organisent dans trois minima locaux de potentiels. La cause de cette différence est un petit défaut dans la symétrie octupolaire des barreaux. / This thesis is part of a project aiming to explore the performance limiting factors of a microwave ion clock. This work is based on the observation and manipulation of a large ion cloud in potentials with different geometries. The purpose is to analyze and transport a large cloud of more than 10^6 ions in a linear radio-frequency trap with several zones. Our group has build a three-zone trap for calcium ion trapping: two quadrupole parts and an octupole part mounted inline. Ions are created in the first quadrupole part and cooled by lasers along the trap symmetry axis. We study the creation of a large ion cloud. The current trapping and cooling parameters limit the maximum size of the cloud to 1,2.10^5 ions. with a rapid and optimized transport protocol, these ions are transfered in the second part of the trap and then in the octupole trap with an efficiency of up to 100%. The result as function of the transport duration shows an asymmetry between the two transport directions. We exploit this feature to add ions in the second or third trap without loss of the already trapped ions. This accumulation technique has allowed to trap 2,5.10^5 ions in the second and third trap. The cooling laser power seems to be the major limiting factor of this number. Finally the observation of the ions in the octupole shows that the cold ions are localised in three different potential wells. This is in contradiction with the hollow structure predicted by the analytical fluid model and molecular dynamics simulations. The cause of this difference is a tiny defect in the octupole symmetry of the RF-electrodes which leads to local minima in the multipole potential.

La communauté de la chimie atmosphérique souffre d'un manque de mesures rapides, fiables résolues spatialement et temporellement pour un large éventail de molécules réactives (radicaux tels que NO2, OH, BrO, IO, etc). En raison de leur forte réactivité, ces molécules contrôlent largement la durée de vie et la concentration de nombreuses espèces clés dans l'atmosphère, et peuvent avoir un impact important sur le climat. Les concentrations de ces radicaux sont extrêmement faibles (ppbv ou moins) et très variable dans le temps et dans l'espace, ce qui impose un véritable défi lors de la détection. Dans la première partie de cette thèse, un spectromètre UV robuste, compacte et transportable est développé, exploitant la technique ML-CEAS pour mesurer à des niveaux très faibles (pptv et même en dessous) des molécules réactives d'importance atmosphérique, en particulier, les radicaux d'oxyde d'halogènes, afin de répondre aux besoins émergents. La technique ML-CEAS est basée sur le couplage d'un laser femtoseconde à blocage de modes à une cavité optique de haute finesse, qui agit comme un piège à photons pour augmenter l'interaction entre la lumière et l'échantillon de gaz intracavité. Cela permet d'améliorer fortement la sensibilité d'absorption. La limite de détection obtenue pour le radical IO est de 20 ppqv pour un temps d'acquisition de 5 minutes, ce qui est un résultat impressionnant. Dans la deuxième partie de cette thèse, une nouvelle technique spectroscopique est développée appelée effet Vernier, qui est également basé sur l'interaction entre un laser femtoseconde à blocage de mode et une cavité optique de haute finesse. Cette technique fournit une sensibilité de détection similaire à la technique ML-CEAS, mais l'avantage est que le nombre des éléments spectraux est donné par la finesse de la cavité optique et donc peut atteindre plusieurs dizaines de milliers. De plus, cette configuration simplifie le montage expérimental par la suppression du spectrographe qui est remplacé par une simple photodiode. Le temps d'acquisition d'un spectre peut être aussi réduit à moins d' 1 ms. / The atmospheric chemistry community suffers a lack of fast, reliable and space resolved measurements for a wide set of reactive molecules (e.g. radicals such as OH, NO3, BrO, IO, etc). Due to their high reactivity, these molecules largely control the lifetime and concentration of numerous key atmospheric species, and may have an important impact on the climate. The concentrations of such radicals are extremely low (ppbv or less) and highly variable in time and space, which imposes a real challenge during the detection. In the first part of this thesis, a compact, robust and transportable UV spectrometer is developed, exploiting the Mode-Locked Cavity Enhanced Absorption Spectroscopy (ML-CEAS) technique to measure pptv and sub-pptv levels of atmospherically important reactive molecules, in particular, halogen oxide radicals, to respond to the emerging needs. The ML-CEAS technique is based on coupling a Mode-Locked femtosecond laser to a high finesse optical cavity, which acts as a photon trap to increase the interaction between the light and the intracavity gas sample, which highly enhances the absorption sensitivity. The detection limit obtained for the IO radical is 20 ppqv (part per quadrillion), which is an impressive result. In the second part of this thesis, a new spectroscopic technique is developed, called Vernier effect, which is also based on the interaction between a mode-locked femtosecond laser with a high finesse optical cavity. This technique provides detection sensitivity similar to that of ML-CEAS technique, but the advantage is that the number of the spectral elements is given by the cavity finesse, so it can reach ten thousands, as well as this technique has a simple setup, where the spectrograph is replaced by a photodiode. Additionally, the time required to measure one output absorption spectrum can be less than 1 ms.

Ce travail de thèse, effectué dans le cadre du projet européen MClocks (http://www.inrim.it/mclocks), reporte le développement et la caractérisation métrologique d’une horloge atomique à cellule de césium de haute performance basée sur le phénomène de piégeage cohérent de population (CPT). Cette horloge exploite un schéma de pompage CPT optimisé nommé push-pull optical pumping (PPOP), permettant la détection de résonances CPT à fort contraste sur la transition d’horloge 0-0. Une caractérisation détaillée des différents éléments de l’horloge est reportée. L’horloge fut exploitée en mode continu (CW) et en mode impulsionnel de type Ramsey. Dans les deux modes de fonctionnement, l’horloge démontre une stabilité relative de fréquence de l’ordre de 2 10−13 τ−1/2 jusque 100 s d’intégration, principalement limitée par des effets de puissance laser. Cette horloge atomique, parmi les meilleures horloges à cellule développées à travers le monde, pourrait trouver des applications pour les systèmes de télécommunications, d’instrumentation, de défense ou navigation par satellite.Cette thèse reporte aussi une technique originale de stabilisation de fréquence laser par spectroscopie sub-Dopplerbi-fréquence en cellule. La plateforme constituée par l’horloge a été utilisée pour mener des tests de physique plus amont incluant la caractérisation par spectroscopie CPT d’une cellule de césium avec un revêtement anti-relaxant OTS (octadecyltrichlorosilane) ou la caractérisation de microcellules à vapeur de césium avec gaz tampon développées à FEMTO-ST pour des horloges atomiques miniatures. / This thesis work, performed in the frame of the MClocks European project (http://www.inrim.it/mclocks), reports the development and metrological characterization of a high-performance Cs vapor cell atomic clock based on coherent population trapping (CPT). The clock uses an optimized CPT pumping scheme, named push-pull optical pumping (PPOP), allowing the detection of high-contrast CPT resonances on the 0-0 magnetic-field insensitive clock transition. A detailed characterization of key components of the clock is reported. The clock was operated in the continuous-wave (CW) regime and in a Ramsey-like pulsed regime. In both regimes, the clock demonstrates a short-term fractional frequency stability at the level of 2 10−13 τ−1/2 up to 100 s averaging time, mainly limited by laser power effects. This CPT clock, ranking among the best microwave vapor cell atomic frequency standards, could find applications in telecommunication, instrumentation, defense or satellite-based navigation systems.This thesis reports also a novel laser frequency stabilization technique using dual-frequency sub-Doppler spectroscopy in a vapor cell. The clock ”platform” has also been used to perform using CPT spectroscopy the characterization of a Cs vapor cell coated with octadecyltrichlorosilane (OTS) or original buffer-gas filled Cs vapor micro-fabricated cells developed in FEMTO-ST for CPT-based miniature atomic clocks.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-11-11T17:33:21Z No. of bitstreams: 0 / Made available in DSpace on 2016-11-11T17:33:21Z (GMT). No. of bitstreams: 0 / O desenvolvimento de sistemas laser com pulsos ultracurtos trouxe a possibilidade de usinagem de estruturas muito pequenas em praticamente qualquer tipo de material. Neste trabalho foi dada continuidade a estudos já iniciados no Centro de Lasers e Aplicações (CLA) com os materiais dielétricos, introduzindo a largura temporal dos pulsos laser como mais uma variável e utilizando os conhecimentos adquiridos para a determinação de limiares de ablação e parâmetros de incubação em alguns metais como: aço AISI 1045, aço inoxidável VI138, cobre eletrolítico e molibdênio. A ausência de calor no processo de ablação dos metais torna-se muito difícil, pois a criação de uma camada de íons é muito prejudicada pela mobilidade eletrônica ao seu redor. Assim a ablação de metais com pulsos ultracurtos, tem como principal mecanismo a explosão de fase associada a outros processos que também contribuem na ablação, porém em menor escala, como a explosão coulombiana e a fusão ultrarrápida. Além disso, propriedades como a constante de acoplamento elétron-fônon e a condutividade térmica assumem um papel importante e devem ser levadas em conta na investigação do processo de ablação dos metais. Este trabalho possibilitou a obtenção de parâmetros de operação nos quais o calor transferido para a rede é minimizado, possibilitando a microusinagem de precisão e alterações controladas na morfologia da superfície de diversos metais. Os resultados propiciaram assim condições para novos desenvolvimentos e aplicações práticas de usinagem com pulsos ultracurtos. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP