Control of high harmonic generation by manipulation of field parameters

?High harmonic generation is a well established technique to investigate the structure and the inner dynamics of atoms and molecules. This thesis describes how the generating field parameters can be manipulated to extend the limits imposed on the technique by the use of traditional laser sources. In this field, with traditional source we mean high intensity, linearly polarised laser pulses at 800 nm. The first parameter to be investigated is the wavelength λ of the generating beam. The unfavourable scaling of the high harmonic yield with λ seems to suggest that high harmonic spectroscopy of atoms and molecules should be restricted to the wavelengths that obviate this problem, and that therefore shorter wavelength should be used. But longer wavelengths, in the mid infrared, present a great advantage respect to shorter ones. The maximum harmonic order that we can obtain is proportional to the ionisation potential of the target and to the wavelength times the intensity of the beam, so a higher number of harmonic can be produced with a longer wavelength than with short, the intensity being equal. This becomes incredibly valuable when the specie under investigation is a molecule with low ionisation potential. To produce high harmonics, a linearly polarised beam is required. If ellipticity is introduced in the beam, the harmonic signal quickly fades out, as non-linearly polarisation in monochromatic beams switches off the mechanism at the basis of high harmonic generation. This is not true if the polarisation of the beam is changed through the introduction of an additional laser beam, perpendicularly polarised respect to the fundamental. In this thesis the additional degree of freedom that this second field implies is investigated by combining the fundamental with its second harmonic and by controlling the relative delay of the two with sub-cycle precision. The key result is that the addition of the second harmonic gives access to the control of the harmonic amplitude and to the time at which the high harmonics are emitted, by simply controlling the relative phase between the two pulses

A Coherent Frequency Comb in the Extreme Ultraviolet

In the course of this work, a system was designed and developed to nonlinearily convert a femtosecond frequency comb laser into the extreme ultraviolet (XUV) spectral range (120-30 nm). The optical frequency comb, for which the nobel prize 2005 was awarded to John Hall and Theodor W. Hänsch, has become an indispensable tool for high precision spectroscopy. With the aid of a mode locked femtosecond laser it is possible to directly and phase coherently link the radio frequency domain and the frequency range of visible light. Today's most accurate time standard, the cesium atomic clock operates in the former and therefore it became possible for the first time to compare arbitrary optical frequencies with our primary time standard and measure them with 15 digits of accuracy. Among other things, this method allowed one of the most accurate test of quantum electrodynamics (QED) today in the course of the determination of the 1S-2S transition frequency of atomic hydrogen that is carried out in one of our labs. But also experiments in the field of ultrafast physics rely on the frequency comb technique to generate precisely controlled optical waveforms. An especially intriguing possibility is to exploit the unique combination of high peak power in the megawatt range and the high spectral quality (on the order of 10^14) of single comb modes of a femtosecond frequency comb. To this end, in the method presented in this thesis, the femtosecond pulse train is coupled to an optical resonator of high finesse. With this trick, the field strength inside the resonator exceeds the driving lasers field by almost an order of magnitude. Enough to efficiently drive a nonlinear process of high order inside a medium of xenon atoms. As a result harmonics of the driving frequency comb up to 15\nth order are generated. The obtained field contains photons with energies exceeding 20~eV, a spectral region which is not or only hard to access by conventional continuous laser source. Therefore the presented XUV frequency comb source brings direct frequency measurements at such high photon energies into the realm of possibility for the first time. In particular, an improved version of the demonstrated source will be used to take the next step in an experiment with a long tradition in our group, the 1S-2S spectroscopy of atomic hydrogen. The generated frequency comb in the vicinity of 60~nm wave length will be used to probe the 1S-2S transition in singly charged helium, a hydrogen like system with larger nuclear charge. From such a measurement it can be expected that, compared to hydrogen, relativistic corrections from the QED theory become more important as the system has higher energies in general. For this reason this could lead to a test of QED with increased sensitivity. Other applications of such a compact and relatively simple coherent source of XUV radiation could be high resolution spectroscopy, XUV holography, but could also lie in the research area of ultrafast physics.Im Verlauf dieser Arbeit wurde ein System entworfen und gebaut, welches einen Femtosekunden-Frequenzkammlaser durch nichtlineare Konversion in den vakuumultravioletten (VUV) Spektralbereich (120-30 nm) überträgt. Der optische Frequenzkamm, für den im Jahr 2005 der Nobelpreis an John Hall und Theodor W. Hänsch verliehen wurde, ist ein unverzichtbares Werkzeug der Präzisionsspektroskopie geworden. Mit der Hilfe eines modengekoppelten Femtosekundenlasers ist es dabei möglich, die Radiofrequenzdomäne, in der die heutzutage genauesten Uhren arbeiten, und den Frequenzbereich des sichtbaren Lichtes miteinander zu verbinden. Damit wurde es erstmals möglich, beliebige optische Frequenzen direkt mit einer Cäsiumatomuhr, unserem primären Zeitstandard, zu vergleichen, sodass optische Frequenzen auf 15 Dezimalstellen genau bestimmt werden konnten. Unter anderem konnte mit dieser Methode einer der genauesten Tests der Quantenelektrodynamik (QED) im Rahmen der Bestimmung der 1S-2S Frequenz von atomarem Wasserstoff in einem unserer Labors durchgeführt werden. Aber auch neuartige Experimente in der Ultrakurzzeitphysik, welche eine präzise Kontrolle der optischen Wellenform benötigen, stützen sich auf die Frequenzkammtechnik. Die Frequenzkammtechnologie in neue Spektralbereiche auszudehnen bietet viele interessante Möglichkeiten. Insbesondere ist es nützlich, die einzigartige Kombination aus hoher Spitzenleistung im Megawattbereich und großer spektraler Güte der einzelnen Kammlinien (Größenordnung 10^14) eines Femtosekundenfrequenzkammes auszunutzen. Zu diesem Zweck wird, bei der in der vorliegenden Arbeit vorgestellten Methode, der Femtosekundenpulszug in einen optischen Resonator hoher Güte eingekoppelt. Durch diesen Trick erhält man innerhalb der Resonatoranordnung Feldstärken, welche die des treibenden Lasers um ein Vielfaches übertreffen und deshalb einen nichtlinearen Prozess hoher Ordnung innerhalb eines Mediums aus Xenonatomen besonders effizient treiben können. Dadurch werden Harmonische des treibenden Frequenzkammes bis zur fünfzehnten Ordnung erzeugt. Das generierte Licht reicht damit bis weit in den VUV-Spektralbereich und enthält Photonen mit Energien von mehr als 20 eV. Dies ist ein Frequenzbereich der herkömmlichen kontinuierlichen Laser nicht oder nur schwer zugänglich ist, sodass mit der vorgestellten Quelle direkte Frequenzmessungen bei hohen Photonenergien erstmals in den Bereich des Möglichen rücken. Insbesondere soll eine weiterentwickelte Variante der in dieser Arbeit demonstrierten VUV Frequenzkammquelle dazu verwendet werden, das traditionsreiche Projekt unserer Arbeitsgruppe, die 1S-2S Spektroskopie an atomarem Wasserstoff, in eine neue Runde zu führen. Der erzeugte Frequenzkamm in der Nähe von 60~nm soll zur direkten 1S-2S Spektroskopie an einfach geladenem Helium, einem wasserstoffähnlichen System mit erhöhter Kernladung, verwendet werden. Von einer solchen Messung erwartet man eine, im Vergleich mit Wasserstoff, erhöhte Empfindlichkeit auf relativistische Korrekturen aus der QED, da das System generell höhere Energien aufweist. Damit könnte ein Test erhöhter Empfindlichkeit für die Theorie der QED realisiert werden. Weitere Anwendungen der kompakten und relativ einfachen kohärenten Quelle für VUV Strahlung könnten in der hochauflösenden Mikroskopie, VUV Holographie aber auch in der Ultrakurzzeitspektroskopie liegen

Alignment of the straw tracking detectors for the Fermilab Muon g−2g-2 experiment and systematic studies for a muon electric dipole moment measurement

The Fermilab Muon $g-2$ experiment is currently preparing for its fourth data-taking period (Run-4). The experiment-wide effort on the analysis of Run-1 data is nearing completion, with the announcement of the first result expected in the coming months. The final goal of the experiment is to determine the muon magnetic anomaly to a precision of 140 ppb. This level of precision will provide indirect evidence of new physics, if the central value agrees with the previously-measured value of the magnetic anomaly. Essential in reducing the systematic uncertainty, through measurements of the muon beam profile, are the in-vacuum straw tracking detectors. A crucial prerequisite in obtaining accurate distributions of the beam profile is the internal alignment of the tracking detectors, which is described in this thesis. As a result of this position calibration, the tracking efficiency has increased by 3%, while the track quality increased by 4%. This thesis also discusses an additional measurement that will be made using the tracking detectors: a search for an electric dipole moment (EDM) of the muon, through the direct detection of an oscillation in the average vertical angle of the electron from the muon decay. An observation of a muon EDM would be evidence of new physics and would provide a new source of CP violation in the charged lepton sector. Essential in measuring the EDM are accurate and precise estimations of potential non-zero radial and longitudinal magnetic fields, which were estimated using the Run-1 data. In addition, a preliminary analysis using the Run-1 data was undertaken to estimate the available precision for the magnetic anomaly measurement using the tracking detectors

Ultra-broadband coherent detection of terahertz pulses via CMOS-compatible solid-state devices.

Dans cette thèse, nous développons et démontrons une nouvelle technique entièrement intégrée ayant pour but de détecter la cohérence des rayons Térahertz (THz), c'est-à-dire des ondes électromagnétiques dont le contenu spectral est compris dans la fenêtre spectrale comprise entre 0.1-10x10¹² Hz. Nous avons appelé cette technique de détection solid-state-biased coherent detection (SSBCD) puisqu'elle est basée sur un état solide et permet d'enregistrer simultanément des informations d'amplitude et de phase d'impulsions THz, même dans le cas de spectres avec ultra-large bande (> 10 THz). En tant que telle, elle peut être potentiellement utilisée dans les systèmes où les impulsions THz servent d’outil de diagnostic ou de supports de signaux, comme dans les domaines de la spectroscopie à résolution temporelle et de l'imagerie, ou encore du traitement du signal. La technique SSBCD est basée sur une plate-forme entièrement compatible avec un processus CMOS. CMOS est une technologie de micro-fabrication couramment utilisée pour la réalisation de circuits électroniques miniaturisés (chips), donc rentables et particulièrement fiables pour la production d'un grand nombre de dispositifs. Par conséquent, son accessibilité rend cette technologie attrayante à la fois pour le public scientifique et industriel. L’avantage principal de la technique présentée ici est la bande passante illimitée dans toute la zone THz (pour une durée d'impulsion laser fixée), permettant ainsi de résoudre tous les problèmes et contraintes de ces solutions THz où l'étape de détection limite principalement les performances du système entier. Après une brève introduction sur la technologie THz et ses différents régimes spectraux, nous passerons en revue toutes les techniques de détection qui ont été récemment démontrées pour obtenir la reconstruction exacte d’états transitoires THz ultra-courts. En particulier, nous nous concentrerons sur les méthodes qui permettent la détection de rayons THz dont les spectres couvrent tout le domaine THz, ou même au-delà (à savoir, le régime de bande ultra-large, c'est-à-dire plus de deux décades). Nous verrons que toutes ces techniques sont essentiellement basées sur les gaz et reposent sur un concept similaire, puisque les configurations à l'état solide, représentant jusqu'ici la fine pointe du domaine de la détection THz, ne sont pas appropriées dans le régime de bande ultra-large, car elles souffrent d'une réponse en fréquence limitée. Ensuite, nous passerons à la description détaillée de trois approches différentes principalement, en soulignant les avantages ou les inconvénients et les limitations, et en concentrant finalement l'attention sur la technique appelée air-biased coherent detection (ABCD). En effet, nous montrerons que notre approche novatrice résout fondamentalement certaines des questions cruciales de la méthode ABCD, en adoptant des matériaux communs à l'état solide (verres) et des structures intégrées particulières. ABCD exploite la non-linéarité de l'air et fonctionne donc à l'énergie de la sonde optique de l'ordre du microjoule et de la tension de polarisation jusqu'à plusieurs kilovolts. Ceci limite son application à des systèmes laser ultra-rapides amplifiés coûteux et volumineux et à des amplificateurs à haute tension lents, qui limitent les performances de bruit et pourraient impliquer un danger pour la santé. Au contraire, nous montrons comment l'utilisation d'un matériau à l'état solide en tant que moyen non-linéaire permet de réduire considérablement non seulement l'exigence d'énergie optique au niveau des nanojoules, mais aussi la taille de la région d'interaction, par rapport à la technique basée sur l'air. Ceci engendre la possibilité d'effectuer la détection THz dans une structure confinée en utilisant des ordres de grandeur de tensions de polarisation inférieure, comparables à celles couramment utilisées pour les antennes photoconductrices. De tels résultats ouvrent la voie à la réalisation d'un dispositif unique et portable pouvant être piloté par des oscillateurs laser (très bonne stabilité du faisceau) et des amplificateurs basse tension, fonctionnant à des fréquences de modulation et de répétition beaucoup plus élevées, qui se traduira par l’augmentation significative de la gamme dynamique et des rapports signal sur bruit. In this dissertation, we develop and demonstrate an innovative and fully integrated technique aimed at the coherent detection of terahertz (THz) radiation, i.e., electromagnetic waves whose frequency content conventionally falls in the spectral window ranging between 0.1-10x10¹² Hz. We named such a detection technique solid-state biased coherent detection (SSBCD), since it is based on a solid-state medium and allows simultaneously recording both the amplitude and phase information of ultrashort THz pulses, i.e. featuring ultra-broadband spectra (> 10 THz). As such, our technique can be successfully used in those systems where THz pulses are employed as either diagnostic tool or signal carriers, such as in the areas of time-resolved spectroscopy and imaging or signal processing. SSBCD is based on platform fully compatible with the CMOS process, i.e. a microfabrication technology commonly employed for the realization of miniaturized electronics circuits (chips), thus being cost-effective and particularly reliable for the production of a great number of devices. Hence, its affordability makes it attractive for both a broad scientific and industrial audience. Indeed, the fundamental advantage of the technique presented here is the unlimited operating bandwidth in the whole THz range (allowed via interaction with ultrashort pulse durations), thus potentially addressing many of the issues and constraints of those THz solutions where the detection scheme represents a bottleneck in terms of the entire system frequency response. Following a brief introduction regarding state-of-the-art of the THz technology and its different spectral regimes of operation, we will mainly review those detection techniques, which have been lately demonstrated to achieve the exact reconstruction of ultrashort THz transients. In particular, we will focus on those methods, which allow the detection of THz radiation, the spectrum of which covers the entire THz domain or even beyond (namely, the ultra-broadband regime). We will see that such particular techniques are essentially gas-based and rely on a similar concept, since the so far available solid-state methods, representing the state-of-the-art in the THz detection area, are not suitable in the ultra-broadband regime, since they suffer a limited frequency response. Then, we will pass to the detailed description of mainly three different approaches, highlighting both advantages and drawbacks or limitations, eventually focusing our attention on the air-biased coherent detection (ABCD) technique. Indeed, we will show that our novel approach essentially overcomes some of the crucial issues of the ABCD method, by adopting particular, yet very common solid-state media (glasses) and plain integrated structures. ABCD exploits the nonlinearity of air and therefore operates at optical probe energies in the order of microjoules and bias voltages as high as several kilovolts. This restricts its application to expensive, bulky amplified ultrafast laser systems, and slow, high voltage amplifiers, which limit the noise performance and imply health hazard (electrical shocks). On the contrary, we show how the employment of CMOS-compatible dielectrics as nonlinear media, allows to dramatically decrease not only the requirement of optical energy to the level of nanojoules but also to greatly shrink down the size of the interaction region between the THz and optical pulses, with respect to the case of air. This results in the possibility to perform the THz detection in a compact structure, by using orders of magnitudes lower bias voltages, comparable to those regularly employed for photoconductive antennas. Such results pave the way to the realization of a unique and portable device that can be potentially driven by laser oscillators (featuring very good beam stability) and low-voltage amplifier, operating at much higher repetition rates and modulation frequencies, which will result in the significant increase of both dynamic range and signal-to-noise ratios. Il presente lavoro di tesi presenta e dimostra una tecnica innovativa e completamente integrata dedita alla rilevazione coerente di radiazioni a frequenze Terahertz (THz), cioè di onde elettromagnetiche il cui contenuto frequenziale cade convenzionalmente nella finestra spettrale compresa tra 0.1-10x10¹² Hz. Tale tecnica è stata battezzata col nome di solid-state-biased coherent detection (SSBCD), dal momento che essa sfrutta le proprietà di un mezzo a stato solido e consente di ricostruire simultaneamente l’informazione sulla fase e sull’ampiezza degli impulsi THz, anche nel caso in cui quest’ultimi siano dotati di spettri a banda cosiddetta “ultra larga” (> 10 THz). Tale metodo di rivelazione può essere utilizzato con successo in quei sistemi in cui gli impulsi THz vengono comunemente impiegati come strumento diagnostico o come portanti di segnali a banda stretta, per esempio nelle aree della spettroscopia nel dominio temporale e nell’elaborazione di immagini o segnali, rispettivamente. La tecnica SSBCD si basa su una piattaforma completamente compatibile con il ben noto processo CMOS, cioè una tecnologia di micro fabbricazione comunemente impiegata per la realizzazione di circuiti elettronici miniaturizzati (chips), essendo quindi economicamente conveniente e particolarmente affidabile per la produzione di un gran numero di dispositivi per singolo processo produttivo. Queste caratteristiche rendono il metodo SSBCD particolarmente attraente per un ampio pubblico sia strettamente accademico sia industriale. Infatti, il suo principale vantaggio è rappresentato da una risposta spettrale estremamente larga, così da coprire l’intera gamma del dominio THz (qualora la durata temporale dell’impulso ottico lo consenta), permettendo potenzialmente di risolvere gran parte dei problemi e dei limiti che caratterizzano le attuali tecniche di rivelazioni, le quali rappresentano invece il collo di bottiglia di molti sistemi che operano a frequenze THz. Di seguito, dopo una breve panoramica sulla tecnologia THz ed i diversi regimi spettrali di funzionamento, esamineremo le principali tecniche di rilevazione, che sono state recentemente dimostrate per ricostruire nel modo più fedele possibile impulsi THz ultra corti. In particolare, ci concentreremo su quei metodi che consentono di ricostruire la forma di impulsi i cui spettri coprono l'intero dominio THz e anche oltre (vale a dire, il regime ultra-broadband). Vedremo che tutte queste tecniche sono essenzialmente basate sull’impiego di gas, sfruttando sostanzialmente lo stesso fenomeno fisico, dal momento che le configurazioni basate sui materiali a stato solido e che rappresentano lo stato dell'arte nell'area della rivelazione THz, non sono adatte per operare nel regime ultra-broadband, essendo caratterizzate da una limitata risposta in frequenza. Pertanto, passeremo alla descrizione in dettaglio di tre approcci diversi, evidenziandone vantaggi e inconvenienti, concentrando infine l’attenzione su un metodo di rivelazione detto air-biased coherent detection (ABCD). In effetti, mostreremo che il nostro nuovo approccio supera essenzialmente alcune problematiche cruciali della tecnica ABCD, grazie all’utilizzo di materiali alquanto usuali (essenzialmente dei vetri) e un’unica semplice struttura integrata. Infatti, il meccanismo intrinseco nell’ABCD sfrutta la non linearità dell’aria, richiedendo perciò energie ottiche dell'ordine dei microjoule e tensioni di polarizzazione pari a diversi kilovolt. Ciò restringe la sua applicazione da un lato a sistemi laser amplificati, che sono costosi e voluminosi, e dall’altro ad amplificatori ad alta tensione, che funzionano a basse frequenze di modulazione (onde quadre), limitando le prestazioni in termini di rumore, nonché comportando rischi per la sicurezza dell’operatore. Al contrario, mostreremo come il metodo SSBCD consente di ridurre drasticamente non solo il fabbisogno di potenza ottica al livello dei nanojoule, ma anche le dimensioni fisiche della regione di interazione fra impulsi THz ed ottici, rispetto al caso dell’ABCD, permettendo così l’utilizzo di livelli di tensione di polarizzazione paragonabili a quelli utilizzati regolarmente per le antenne fotoconduttrici. Tali risultati spianano la strada alla realizzazione di un dispositivo unico e portatile che può essere potenzialmente pilotato da oscillatori laser (che generano fasci laser di migliore stabilità ma a ben più basse energie) e amplificatori a bassa tensione, operanti a frequenze di modulazione molto più elevate, portando così ad un significativo aumento della dinamica dei segnali rivelati e dei loro rapporti segnale-rumore

Yb ion trap experimental set-up and two-dimensional ion trap surface array design towards analogue quantum simulations

Ions trapped in Paul traps provide a system which has been shown to exhibit most of the properties required to implement quantum information processing. In particular, a two-dimensional array of ions has been shown to be a candidate for the implementation of quantum simulations. Microfabricated surface geometries provide a widely used technology with which to create structures capable of trapping the required two-dimensional array of ions. To provide a system which can utilise the properties of trapped ions a greater understanding of the surface geometries which can trap ions in two-dimensional arrays would be advantageous, and allow quantum simulators to be fabricated and tested. In this thesis I will present the design, set-up and implementation of an experimental apparatus which can be used to trap ions in a variety of different traps. Particular focus will be put on the ability to apply radio-frequency voltages to these traps via helical resonators with high quality factors. A detailed design guide will be presented for the construction and operation of such a device at a desired resonant frequency whilst maximising the quality factor for a set of experimental constraints. Devices of this nature will provide greater filtering of noise on the rf voltages used to create the electric field which traps the ions which could lead to reduced heating in trapped ions. The ability to apply higher voltages with these devices could also provide deeper traps, longer ion lifetimes and more efficient cooling of trapped ions. In order to efficiently cool trapped ions certain transitions must be known to a required accuracy. In this thesis the 2S1/2 → 2P1/2 Doppler cooling and 2D3/2 → 2D[3/2]1/2 repumping transition wavelengths are presented with a greater accuracy then previous work. These transitions are given for the 170, 171, 172, 174 and 176 isotopes of Yb+. Two-dimensional arrays of ions trapped above a microfabricated surface geometry provide a technology which could enable quantum simulations to be performed allowing solutions to problems currently unobtainable with classical simulation. However, the spin-spin interactions used in the simulations between neighbouring ions are required to occur on a faster time-scale than any decoherence in the system. The time-scales of both the ion-ion interactions and decoherence are determined by the properties of the electric field formed by the surface geometry. This thesis will show how geometry variables can be used to optimise the ratio between the decoherence time and the interaction time whilst simultaneously maximising the homogeneity of the array properties. In particular, it will be shown how the edges of the geometry can be varied to provide the maximum homogeneity in the array and how the radii and separation of polygons comprising the surface geometry vary as a function of array size for optimised arrays. Estimates of the power dissipation in these geometries will be given based on a simple microfabrication

The ultrafast nonlinear response of air molecules and its effect on femtosecond laser plasma filaments in atmosphere

The nonlinear propagation of an intense ultrafast laser pulse in atmosphere or other gas media leads to filamentation, a phenomenon useful for applications such as remote sensing, spectral broadening and shaping of ultrashort laser pulses, terahertz generation, and guiding of electrical discharges. Axially extended optical filaments result from the dynamic balance between nonlinear self-focusing in the gas and refraction from the free electron distribution generated by laser ionization. In the air, self-focusing is caused by two nonlinear optical processes: (1) the nearly-instantaneous, electronic response owing to the distortion of electron orbitals, and (2) the delayed, orientational effect due to the torque applied by the laser field on the molecules with anisotropic polarizability. To study their roles in filamentary propagation as well as influences on plasma generation in atmosphere, these effects were experimentally examined by a sensitive, space- and time-resolved technique based on single-shot supercontinuum spectral interferometry (SSSI), which is capable of measuring ultrafast refractive index shift in the optical medium. A proof-of-principle experiment was first performed in optical glass and argon gas, showing good agreement between the laser pulse shape and the refractive index temporal evolution owing to pure instantaneous n2 effect. Then the delayed occurrence of the molecular alignment in the temporal vicinity of the femtosecond laser pulse, as well as the subsequent periodic &ldquo;alignment revivals&rdquo; due to the coherently excited rotational wavepacket were measured in various linear gas molecules, and the results agreed well with quantum perturbation theory. It was found that the magnitude of orientational response is much higher than the electronic response in N2 and O2, which implies that the molecular alignment is the dominant nonlinear effect in atmospheric propagation when the pulse duration is longer than &sim;40 fs, the rotational response timescale of air molecules. Realizing the possibility of manipulating plasma generation by aligning air molecules, the molecular orientational effect was further investigated by a technique developed to directly measure, for the first time, the radial and axial plasma density in a meter-long filament. The experiment was performed using both &sim;40 fs and &sim;120 fs laser pulse durations while keeping the peak power fixed under various focusing conditions, and the alignment-assisted filamenation with &sim;2&ndash;3 times plasma density and much longer axial length was consistently observed with the longer pulse, which experienced larger refractive index shift and thus stronger self-focusing. Simulations reproduced the axial electron density measurements well for both long and short pulse durations, when using a peak magnitude of instantaneous response as <15% of the rotational response

Remote and Local Entanglement of Ions using Photons and Phonons

The scaling of controlled quantum systems to large numbers of degrees of freedom is one of the long term goals of experimental quantum information science. Trapped-ion systems are one of the most promising platforms for building a quantum information processor with enough complexity to enable novel computational power, but face serious challenges in scaling up to the necessary numbers of qubits. In this thesis, I present both technical and operational advancements in the control of trapped-ion systems and their juxtaposition with photonic modes used for quantum networking. After reviewing the basic physics behind ion trapping, I then describe in detail a new method of implementing Raman transitions in atomic systems using optical frequency combs. Several dierent experimental setups along with simple theoretical models are reviewed and the system is shown to be capable of full control of the qubit-oscillator system. Two-ion entangling operations using optical frequency combs are demonstrated along with an extension of the operation designed to suppress certain experimental errors. I then give an overview of how spatially separated ions can be entangled using a photonic interconnect. Experimental results show that pulsed excitation of trapped ions provide an excellent single photon source that can be used as a heralded entangling gate between macroscopically separated systems. This heralded entangling gate is used to show a violation of a Bell inequality while keeping the detection loophole closed and can be used a source private random numbers. Finally, the coherent Coulomb force-based gates are combined with the probabilistic photon-based gates in a proof of concept experiment that shows the feasibility of a distributed ion-photon network

Spectroscopy and Dynamics of Sulphur-Containing Organic Chromophores

The work outlined in this thesis aims to shed light on the electronic structure and dynamics of several sulphur-containing organic chromophores. A general introduction to molecular photochemistry and photoelectron spectroscopy of neutral molecules and anions is provided in Chapter 1. For the work reported here, two experimental apparatus are used: a pulsed molecular beam for the preparation of cold, gas-phase neutral molecules and an electrospray ionisation mass spectrometer for the production of anions. Both of these apparatus employ photoelectron spectroscopy with velocity map imaging in order to measure the energy and angular distribution of photoelectrons, and are detailed in Chapter 2. For the molecular beam apparatus, UV femtosecond lasers are used for either one-colour, static or two-colour, time-resolved photoelectron spectroscopic measurements. The electrospray apparatus utilises nanosecond lasers for one-photon detachment. Chapter 3 of this thesis describes the static and time-resolved photoelectron spectroscopy performed on a molecular beam of neutral thiophene. These measurements have allowed us to gain insight into the molecular energy levels involved in photoexcitation, as well as the ultrafast dynamics. Chapter 4 describes use of the molecular beam to produce gas-phase thiophenol molecules for static photoelectron measurements, enabling the determination of the electronically excited states following direct photoexcitation. This work is supplemented by excited state theory calculations, providing a more complete picture of the electronic structure and dynamics of thiophenol. Finally, Chapter 5 reports on the use of electrospray ionisation to produce anions of 6-mercaptopurine, which were interrogated using a nanosecond optical parametric oscillator for photoelectron spectroscopic studies. The experimental measurements are also supported by excited state calculations. The combination of experiment and theory has allowed for a dominant deprotomer to be assigned to the features in the photoelectron spectra. Additionally, methylated analogues of the 6-mercaptopurine anion were investigated to aid in identifying the dominant anionic species. Overall, this thesis provides valuable insight into the electronic structure and dynamics of sulphur-containing organic chromophores. The combination of angle-resolved photoelectron spectroscopy with computational chemistry has helped to provide a comprehensive understanding the interaction of light with these complex molecules. The results of this work can find application in a variety of scientific fields, from biophysics to materials science