Stimulated emission depletion microscopy with optical fibers

Imaging at the nanoscale and/or at remote locations holds great promise for studies in fields as disparate as the life sciences and materials sciences. One such microscopy technique, stimulated emission depletion (STED) microscopy, is one of several fluorescence based imaging techniques that offers resolution beyond the diffraction-limit. All current implementations of STED microscopy, however, involve the use of free-space beam shaping devices to achieve the Gaussian- and donut-shaped Orbital Angular Momentum (OAM) carrying beams at the desired colors –-- a challenging prospect from the standpoint of device assembly and mechanical stability during operation. A fiber-based solution could address these engineering challenges, and perhaps more interestingly, it may facilitate endoscopic implementation of in vivo STED imaging, a prospect that has thus far not been realized because optical fibers were previously considered to be incapable of transmitting the OAM beams that are necessary for STED. In this thesis, we investigate fiber-based STED systems to enable endoscopic nanoscale imaging. We discuss the design and characteristics of a novel class of fibers supporting and stably propagating Gaussian and OAM modes. Optimization of the design parameters leads to stable excitation and depletion beams propagating in the same fiber in the visible spectral range, for the first time, with high efficiency (>99%) and mode purity (>98%). Using the fabricated vortex fiber, we demonstrate an all-fiber STED system with modes that are tolerant to perturbations, and we obtain naturally self-aligned PSFs for the excitation and depletion beams. Initial experiments of STED imaging using our device yields a 4-fold improvement in lateral resolution compared to confocal imaging. In an experiment in parallel, we show the means of using q-plates as free-space mode converters that yield alignment tolerant STED microscopy systems at wavelengths covering the entire visible spectrum, and hence dyes of interest in such imaging schematics. Our study indicates that the vortex fiber is capable of providing an all-fiber platform for STED systems, and for other imaging systems where the exploitation of spatio-spectral beam shaping is required

Novel Insights into Orbital Angular Momentum Beams: From Fundamentals, Devices to Applications

It is well-known by now that the angular momentum carried by elementary particles can be categorized as spin angular momentum (SAM) and orbital angular momentum (OAM). In the early 1900s, Poynting recognized that a particle, such as a photon, can carry SAM, which has only two possible states, i.e., clockwise and anticlockwise circular polarization states. However, only fairly recently, in 1992, Allen et al. discovered that photons with helical phase fronts can carry OAM, which has infinite orthogonal states. In the past two decades, the OAM-carrying beam, due to its unique features, has gained increasing interest from many different research communities, including physics, chemistry, and engineering. Its twisted phase front and intensity distribution have enabled a variety of applications, such as micromanipulation, laser beam machining, nonlinear matter interactions, imaging, sensing, quantum cryptography and classical communications. This book aims to explore novel insights of OAM beams. It focuses on state-of-the-art advances in fundamental theories, devices and applications, as well as future perspectives of OAM beams

Mode division multiplexing based on ring core optical fibers

The unique modal characteristics of ring core fibers (RCFs) potentially enable the implementation of mode-division multiplexing (MDM) schemes that can increase optical data transmission capacity with either low-complexity modular multi-input multi-output (MIMO) equalization or no MIMO equalization. This paper attempts to present a comprehensive review of recent research on the key aspects of RCF-based MDM transmission. Starting from fundamental fiber modal structures, a theoretical comparison between RCFs and conventional step-index and graded-index multi-mode fibers in terms of their MDM capacity and the associated MIMO complexity is given first as the underlining rationale behind RCF-MDM. This is followed by a discussion of RCF design considerations for achieving high-mode channel count and low crosstalk performances in either MIMO-free or modular MIMO transmission schemes. The principles and implementations of RCF mode (de-)multiplexing devices are discussed in detail, followed by RCF-based optical amplifiers culminating in MIMO-free or modular-MIMO RCF-MDM data transmission schemes. A discussion on further research directions is also given

High-Performance On-Chip Microwave Photonic Signal Processing Using Linear and Nonlinear Optics

Manipulating and processing radio-frequency (RF) signals using integrated photonic devices has recently emerged as a paradigm-shifting technology for future microwave applications. This emerging technique is referred to as integrated microwave photonics (IMWP) which enables the high-frequency processing and unprecedentedly wideband tunability in compact photonic circuits, with significantly enhanced stability and robustness. However, to find widespread applications, the performance of IMWP devices must meet or exceed the achievable performance of conventional electronic counterparts. The work presented in this thesis investigates high-performance IMWP signal processing from two aspects: the optimized IMWP processing schemes and the photonic integration. Firstly, we explore novel schemes to improve the performance of chip-based microwave photonic subsystems, such as RF delay lines and RF filters which are basic building blocks of RF systems. A phase amplification technique is demonstrated to achieve a Si3N4 chip-based RF time delay with a delay tuning speed at gigahertz level. A new scheme to achieve an all-optimized RF photonic notch filter is demonstrated, producing a record-high RF link performance and complete functionalities. To unlock the potential of RF signal processing, we investigate a new filter concept of pairing linear and nonlinear optics for a high-performance RF photonic filter. To reduce the footprint of the novel IMWP filter, the photonic integration of both the ring resonators and Brillouin-active circuits on the same photonic chip is achieved. To eliminate the use of integrated optical circulators for on-chip SBS, on-chip backward inter-modal stimulated Brillouin scattering is predicted and experimentally demonstrated in a Si-Chalcogenide hybrid integrated photonic platform. The study and demonstrations presented in this thesis make the first viable step towards high-performance IMWP signal processing for real-world RF applications

Cold-Atom Loading of Hollow-Core Photonic Crystal Fibre for Quantum Technologies

Ultra-strong light-atom interaction is a key resource for numerous applications in quantum-information processing, nonlinear optics, and quantum sensing. Maximising the strength of the interaction requires optimising the combination of light-atom coherent interaction time, spatial overlap between the optical mode and the atomic cross section, and the number of participating atoms. An exciting approach to achieving these goals is to use a collection of laser-cooled atoms inside a hollow-core photonic crystal fibre. Here the tight transverse confinement provided by fibre guarantees overlap between the atomic sample and guided optical modes over an arbitrarily long distance. Laser cooling improves the effective atom number of the sample by increasing the fraction that participate in the interaction and significantly improves the coherent interaction time by reducing the spatial decoherence rate of the ensemble. This project focuses around the development of an apparatus that realises the lasercooling, trapping, and loading of atoms into a kagome-lattice hollow-core fibre. In this thesis we describe the development of the elements required to realise this task, including the vacuum system, laser sources, computer oversight, and theoretical models employed. The resulting platform is capable of achieving the ultra-high optical depths required for exciting quantum-optics applications such as long-lived coherent optical pulse storage. We have demonstrated high-efficiency transport of cold rubidium atoms from a magneto-optical trap into a hollow-core fibre, measuring a peak optical depth of 600 with only 3£106 atoms. These experiments were guided by a Monte-Carlo simulation that has been shown to have excellent agreement with the physical system. The results show that this platform is in an excellent position to investigate coherent optical phenomena at the few-photon level. Along the way we investigated the application of light-shift engineering to both measure and compensate for the perturbative effects the strong light fields present in the experiment have on atomic states. We extend the ‘magic-wavelength’ technique used in the atomic lattice clock community to nullify the lineshape broadening of the target ensemble by introducing an additional light field. This allows the technique to be implemented in a broad range of atomic species and transitions, where the original technique was only accessible for limited species with specific energy-level structures. We also take advantage of light-shift engineering to extract a detailed model of the spatial distribution of an optically-trapped ensemble through a simple spectroscopic technique. We use this model to infer the temperature, coherence time, and number of atoms in the trap in addition to the depth of the trap itself. Experimentally we demonstrate this on our cold-atom-filled fibre platform, showing that this information can be extracted from a system with limited optical access and where conventional techniques cannot be applied. The apparatus and experimental techniques we have developed place this project in an excellent position to perform cutting-edge research in the fields of quantum information processing and nonlinear optics.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

Optics in Our Time

Optics, Lasers, Photonics, Optical Devices; Quantum Optics; Popular Science in Physics; History and Philosophical Foundations of Physic

Engineering aperiodic spiral order for photonic-plasmonic device applications

Thesis (Ph.D.)--Boston UniversityDeterministic arrays of metal (i.e., Au) nanoparticles and dielectric nanopillars (i.e., Si and SiN) arranged in aperiodic spiral geometries (Vogel's spirals) are proposed as a novel platform for engineering enhanced photonic-plasmonic coupling and increased light-matter interaction over broad frequency and angular spectra for planar optical devices. Vogel's spirals lack both translational and orientational symmetry in real space, while displaying continuous circular symmetry (i.e., rotational symmetry of infinite order) in reciprocal Fourier space. The novel regime of "circular multiple light scattering" in finite-size deterministic structures will be investigated. The distinctive geometrical structure of Vogel spirals will be studied by a multifractal analysis, Fourier-Bessel decomposition, and Delaunay tessellation methods, leading to spiral structure optimization for novel localized optical states with broadband fluctuations in their photonic mode density. Experimentally, a number of designed passive and active spiral structures will be fabricated and characterized using dark-field optical spectroscopy, ellipsometry, and Fourier space imaging. Polarization-insensitive planar omnidirectional diffraction will be demonstrated and engineered over a large and controllable range of frequencies. Device applications to enhanced LEDs, novel lasers, and thin-film solar cells with enhanced absorption will be specifically targeted. Additionally, using Vogel spirals we investigate the direct (i.e. free space) generation of optical vortices, with well-defined and controllable values of orbital angular momentum, paving the way to the engineering and control of novel types of phase discontinuities (i.e., phase dislocation loops) in compact, chip-scale optical devices. Finally, we report on the design, modeling, and experimental demonstration of array-enhanced nanoantennas for polarization-controlled multispectral nanofocusing, nanoantennas for resonant near-field optical concentration of radiation to individual nanowires, and aperiodic double resonance surface enhanced Raman scattering substrates

Enabling Real-Time Terahertz Imaging With Advanced Optics and Computational Imaging

La bande des térahertz est une région particulière du spectre électromagnétique comprenant les fréquences entre 0.1 THz à 10 THz, pour des longueurs d’onde respectives de 3 mm à 30 um. Malgré tout l’intérêt que cette région a suscité au cours de la dernière décennie, de grands obstacles demeurent pour une application plus généralisée de la radiation THz dans les applications d’imagerie. Cette thèse aborde le problème du temps d’acquisition d’une image THz. Notre objectif principal sera de développer des technologies et techniques pour permettre l’imagerie THz en temps réel. Nous débutons cette thèse avec une revue de littérature approfondie sur le sujet de l’imagerie THz en temps réel. Cette revue commence par énumérer plusieurs sources et détecteurs THz qui peuvent immédiatement être utilisés en imagerie THz. Nous détaillons par la suite plusieurs modalités d’imagerie développés au cours des dernières années : 1) Imagerie THz en transmission, en réflexion et de conductivité, 2) imagerie THz pulsée, 3) imagerie THz par tomographie computationnelle et 4) imagerie THz en champ proche. Nous discutons par la suite plus en détail à propos de technologies habilitantes pour l’imagerie THz en temps réel. Pour cela, nous couvrons trois différents axes de recherche développés en littérature : 1)Imagerie en temps réel de spectroscopie THz dans le domaine du temps, 2) caméras THz et 3) imagerie en temps réel avec détecteur à pixel unique. Nous présentons ensuite le système d’imagerie que nous avons développé pour les démonstrations expérimentales de cette thèse. Ce système est basé sur la spectroscopie THz en temps réel et permet donc d’obtenir des images hyperspectrales en amplitude et en phase. Il utilise des antennes photoconductrices pour l’émission et la détection de la radiation THz. En outre, le détecteur est fibré, ce qui permet de le déplacer spatialement pour construire des images. Nous couvrons aussi brièvement plusieurs techniques de fabrication avancées que nous avons utilisées : impression 3D par filament, stéréolithographie, machinage CNC, gravure/découpe laser et transfert de métal par toner. Nous portons ensuite notre attention à l’objectif principal de cette thèse à travers trois démonstrations distinctes. Premièrement, nous concevons des composants THz à faibles pertes en utilisant des matériaux poreux. L’absence de détecteurs THz ultra-sensibles implique que les pertes encourues dans un système d’imagerie sont hautement indésirables. En effet, un moyennage temporel est généralement fait pour extraire de faibles signaux THz sévèrement enfouis sous le bruit technique. Ceci a pour impact de diminuer le nombre d’images à la seconde. ----------Abstract The terahertz band is a region of the electromagnetic spectrum comprising frequencies between 0.1 THz to 10 THz for respective wavelengths of 3 mm to 30 um. Despite all the interest and potential generated in the past decade for applications of this spectral band, there are still major hurdles impeding a wider use of THz radiation for imaging. This thesis addresses the problem of image acquisition time. Our main objective is to develop technologies and techniques to achieve real-time THz imaging. We start this thesis with a comprehensive review of the scientific literature on the topic of realtime THz imaging. This review begins by listing some off-the-shelf THz sources and detectors that could be readily used in THz imaging. We then detail some key imaging modalities developed in the past years: 1) THz transmission, reflection and conductivity imaging, 2) THz pulsed imaging, 3) THz computed tomography, and 4) THz near-field imaging. We then discuss practical enabling technologies for real-time THz imaging: 1) Real-time THz timedomain spectroscopy imaging, 2) THz cameras, and 3) real-time THz single-pixel imaging. We then present our fiber-coupled THz time-domain spectroscopy imaging setup. This system is used throughout the thesis for experimental demonstrations. We also briefly overview many advanced fabrication techniques that we have used, namely fused deposition modeling,stereolithography, CNC machining, laser cutting/engraving and metal transfer using toner. We then turn to the main objective of this thesis with three distinct demonstrations. First, we design low-loss THz components using porous media. The losses incurred in the imaging system are highly undesirable due to the lack of sensitive THz detectors. Indeed, time averaging is generally performed in order to retrieve THz signals severely buried under noise,which in return reduce the framerate. We propose to use low-refractive index subwavelength inclusions (air holes) in a solid dielectric material to build optical components. We show that these components have smaller losses than their all-solid counterparts with otherwise identical properties. We fabricate a planar porous lens and an orbital angular momentum phase plate, and we use our imaging system to characterize their effects on the THz beam. Second, we demonstrate a spectral encoding technique to significantly reduce the required number of measurements to reconstruct a THz image in a single-pixel detection scheme

Introduction to modern instrumentation: for hydraulics and environmental sciences

Preface Natural hazards and anthropic activities threaten the quality of the environment surrounding the human being, risking life and health. Among the different actions that must be taken to control the quality of the environment, the gathering of field data is a basic one. In order to obtain the needed data for environmental research, a great variety of new instruments based on electronics is used by professionals and researchers. Sometimes, the potentials and limitations of this new instrumentation remain somewhat unknown to the possible users. In order to better utilize modern instruments it is very important to understand how they work, avoiding misinterpretation of results. All instrument operators must gain proper insight into the working principles of their tools, because this internal view permits them to judge whether the instrument is appropriately selected and adequately functioning. Frequently, manufacturers have a tendency to show the great performances of their products without advising their customers that some characteristics are mutually exclusive. Car manufacturers usually show the maximum velocity that a model can reach and also the minimum fuel consumption. It is obvious for the buyer that both performances are mutually exclusive, but it is not so clear for buyers of measuring instruments. This book attempts to make clear some performances that are not easy to understand to those uninitiated in the utilization of electronic instruments. Technological changes that have occurred in the last few decades are not yet reflected in academic literature and courses; this material is the result of a course prepared with the purpose of reducing this shortage. The content of this book is intended for students of hydrology, hydraulics, oceanography, meteorology and environmental sciences. Most of the new instruments presented in the book are based on electronics, special physics principles and signal processing; therefore, basic concepts on these subjects are introduced in the first chapters (Chapters 1 to 3) with the hope that they serve as a complete, yet easy-to-digest beginning. Because of this review of concepts it is not necessary that the reader have previous information on electronics, electricity or particular physical principles to understand the topics developed later. Those readers with a solid understanding of these subjects could skip these chapters; however they are included because some students could find them as a useful synthesis. Chapter 4 is completely dedicated to the description of transducers and sensors frequently used in environmental sciences. It is described how electrical devices are modified by external parameters in order to become sensors. Also an introduction to oscillators is presented because they are used in most instruments. In the next chapters all the information presented here is recurrently referred to as needed to explain operating principles of instruments. Unauthenticated Download Date | 10/12/14 9:29 PM VIII Preface Chapters 1 to 4 are bitter pills that could discourage readers interested in the description of specific instruments. Perhaps, those readers trying this book from the beginning could abandon it before arriving at the most interesting chapters. Therefore, they could read directly Chapters 5 to 11, going back as they feel that they need the knowledge of the previous chapters. We intended to make clear all the references to the previous subjects needed to understand each one of the issues developed in the later chapters. Chapter 5 contributes to the understanding of modern instrumentation to measure flow in industrial and field conditions. Traditional mechanical meters are avoided to focus the attention on electronic ones, such as vortex, electromagnetic, acoustic, thermal, and Coriolis flowmeters. Special attention is dedicated to acoustic Doppler current profilers and acoustic Doppler velocimeters. Chapter 6 deals with two great subjects; the first is devoted to instruments for measuring dynamic and quasi static levels in liquids, mainly water. Methods to measure waves at sea and in the laboratory are explained, as well as instruments to measure slow changes such as tides or piezometric heads for hydrologic applications. The second subject includes groundwater measurement methods with emphasis on very low velocity flowmeters which measure velocity from inside a single borehole. Most of them are relatively new methods and some are based on operating principles described in the previous chapter. Seepage meters used to measure submarine groundwater discharge are also presented. Chapter 7 presents methods and instruments for measuring rain, wind and solar radiation. Even though the attention is centered on new methods, some traditional methods are described not only because they are still in use, and it is not yet clear if the new technologies will definitely replace them, but also because describing them permits their limitations and drawbacks to be better understood. Methods to measure solar radiation are described from radiation detectors to complete instruments for total radiation and radiation spectrum measurements. Chapter 8 is a long chapter where we have tried to include most remote measuring systems useful for environmental studies. It begins with a technique called DTS (Distributed Temperature Sensing) that has the particularity of being remote, but where the electromagnetic wave propagates inside a fibre optic. The chapter follows with atmosphere wind profilers using acoustic and electromagnetic waves. Radio acoustic sounding systems used to get atmospheric temperature profiles are explained in detail as well as weather radar. Methods for ocean surface currents monitoring are also introduced. The chapter ends with ground penetrating radars. Chapter 9 is an introduction to digital transmission and storage of information. This subject has been reduced to applications where information collected by field instruments has to be conveyed to a central station where it is processed and stored. Some insight into networks of instruments is developed; we think this information will help readers to select which method to use to transport information from field to office, by means of such diverse communication media as fibre optic, digital telephony, Unauthenticated Download Date | 10/12/14 9:29 PM Preface IX GSM (Global System for Mobile communications), satellite communications and private radio frequency links. Chapter 10 is devoted to satellite-based remote sensing. Introductory concepts such as image resolution and instrument?s scanning geometry are developed before describing how passive instruments estimate some meteorological parameters. Active instruments are presented in general, but the on-board data processing is emphasized due to its importance in the quality of the measurements. Hence, concepts like Synthetic Aperture Radar (SAR) and Chirp Radar are developed in detail. Scatterometers, altimeters and Lidar are described as applications of the on-board instruments to environmental sciences. Chapter 11 attempts to transfer some experiences in field measuring to the readers. A pair of case studies is included to encourage students to perform tests on the instruments before using them. In this chapter we try to condense our ideas, most of them already expressed throughout the book, about the attitude a researcher should have with modern instruments before and after a measuring field work. As can be inferred from the foregoing description the book aims to provide students with the necessary tools to adequately select and use instruments for environmental monitoring. Several examples are introduced to advise future professionals and researchers on how to measure properly, so as to make sure that the data recorded by the instruments actually represents the parameters they intend to know. With this purpose, instruments are explained in detail so that their measuring limitations are recognized. Within the entire work it is underlined how spatial and temporal scales, inherent to the instruments, condition the collection of data. Informal language and qualitative explanations are used, but enough mathematical fundamentals are given to allow the reader to reach a good quantitative knowledge. It is clear from the title of the book that it is a basic tool to introduce students to modern instrumentation; it is not intended for formed researchers with specific interests. However, general ideas on some measuring methods and on data acquisition concepts could be useful to them before buying an instrument or selecting a measuring method. Those readers interested in applying some particular method or instrument described in this book should consider these explanations just as an introduction to the subject; they will need to dig deeper in the specific bibliography before putting hands on.Fil: Guaraglia, Dardo Oscar. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Hidraulica. Area Hidraulica Basica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Pousa, Jorge Lorenzo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Oceanografía Costera y Estuarios; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Precision spectroscopy of the 2S-nP transitions in atomic hydrogen

Präzisionsspektroskopie an atomarem Wasserstoff ist eine wichtige Methode die Quantenelektrodynamik (QED) gebundener Systeme, einer der Bausteine des Standardmodells, zu testen. Im einfachsten Fall besteht ein solcher Test aus dem Vergleich einer gemessenen Übergangsfrequenz mit der Vorhersage der QED, welche für das Wasserstoffatom mit sehr hoher Präzision berechnet werden kann. Diese Berechnungen benötigen allerdings bestimmte physikalische Konstanten als Eingangsparameter, unter anderem die Rydberg-Konstante sowie den Protonenladungsradius, welche gegenwärtig beide zu einem großen Teil selbst durch Wasserstoffspektroskopie bestimmt werden. Für einen Test der QED ist es deshalb notwendig, die Übergangsfrequenzen von mindestens drei verschiedenen Übergängen zu bestimmen. Gleichermaßen ist ein Vergleich der aus Messungen verschiedener Übergänge bestimmten Werte für die Rydberg-Konstante und den Protonenladungsradius ein Test der QED. Hierzu wurde in dieser Arbeit Laserspektroskopie der optischen 2S-nP-Übergänge durchgeführt. Da es sich bei diesen Übergängen um Ein-Photonen-Übergänge handelt, sind sie von einem anderen Satz an systematischen Effekten betroffen als Zwei-Photonen-Übergänge, auf denen die meisten anderen spektroskopischen Messungen an Wasserstoff basieren. Um zu einem Test der QED beitragen zu können, muss ihre Übergangsfrequenz mit einer relativen Unsicherheit in der Größenordnung von eins zu 10^12 bestimmt werden, in absoluten Einheiten etwa auf 1 kHz. Dies ist etwa 10000 Mal kleiner als die relativ große natürliche Linienbreite der 2S-nP-Übergänge, weshalb für eine erfolgreiche Messung sowohl ein sehr großes Signal-zu-Rausch-Verhältnis als auch ein detailliertes theoretisches Verständnis der Linienform der beobachteten Resonanz notwendig ist. Die 2S-nP-Übergänge wurden an einem kryogenen Strahl aus Wasserstoffatomen, die optisch in den metastabilen 2S-Zustand angeregt wurden, untersucht. Der Atomstrahl wurde rechtwinklig mit zwei gegenläufigen Spektroskopie-Laserstrahlen gekreuzt, die die Atome weiter in den nP-Zustand anregten. Die Fluoreszenz des anschließenden, raschen spontanen Zerfalls diente als Messsignal. Die Anregung mit zwei gegenläufigen Strahlen führt zu zwei Dopplerverschiebungen der gleichen Größe, aber mit umgekehrten Vorzeichen, die sich damit aufheben. Eine nach der Geschwindigkeit der Atome aufgelöste Detektion erlaubte die Bestimmung eventuell verbliebener Dopplerverschiebungen, die im Rahmen der Messunsicherheit jedoch für beide unten vorgestellten Messungen ausgeschlossen werden konnten. In einem ersten Experiment wurde der 2S-4P-Übergang untersucht. Quanteninterferenz zwischen benachbarten atomaren Resonanzen führte zu subtilen Verformungen der Linienform, die sich aufgrund der sehr hohen Auflösung bezogen auf die Linienbreite als signifikant herausstellten. Die durch diese Verformungen verursachten Linienverschiebungen konnten direkt beobachtet und mit einem auf Störungstheorie basierenden Linienformmodell entfernt werden. Somit konnte die Übergangsfrequenz mit einer relativen Messungenauigkeit von 4 zu 10^12 bestimmt werden. In Kombination mit der sehr präzise gemessenen 1S-2S-Übergangsfrequenz erlaubte dies die zu dem Zeitpunkt präziseste Bestimmung der Rydberg-Konstante und des Protonenladungsradius mittels Spektroskopie an atomarem Wasserstoff. Darüber hinaus wurde eine gute Übereinstimmung mit dem durch Spektroskopie an myonischem Wasserstoff bestimmten, sehr viel präziseren Wert für den Protonenladungsradius festgestellt, welcher signifikant von den vorherigen Daten aus (elektronischem) Wasserstoff abweicht und damit zu Zweifeln an der Gültigkeit der QED geführt hatte. Der myonische Wert für den Protonenladungsradius wurde seitdem von weiteren Experimenten bestätigt. Die 2S-4P-Messung wird im Anhang dieser Arbeit behandelt. Trotz des hohen Signal-zu-Rausch-Verhältnisses war die Genauigkeit der 2S-4P-Messung durch die Zählrate des Messsignals limitiert. Um die Präzision weiter zu erhöhen, war ein Übergang mit kleinerer Linienbreite und ein verbessertes experimentelles Signal notwendig. Deshalb wurde mit der Untersuchung des 2S-6P-Übergangs, welcher eine dreimal kleinere natürliche Linienbreite bietet, begonnen. Der Atomstrahlapparat wurde modifiziert, wodurch eine entsprechende Reduktion der experimentell beobachteten Linienbreite und ein fast eine Größenordnung höherer Fluss an langsamen Atomen im Atomstrahl erreicht werden konnte. Zusammen mit einer Neukonstruktion des Detektors führte dies im Vergleich zur 2S-4P-Messung zu einem bis zu 16-fach höherem Signal und machte damit den Weg zu höherer Präzision frei. Um diese Präzision zu ermöglichen, war darüber hinaus eine Weiterentwicklung der Dopplerverschiebungsunterdrückung notwendig. Dazu wurde ein Faserkollimator entwickelt, der eine exzellente Strahlqualität der Spektroskopie-Laserstrahlen bei der neuen Übergangswellenlänge von 410 nm bietet. Dies ermöglichte eine Messung der 2S-6P-Übergangsfrequenz mit einer statistischen Unsicherheit von 430 Hz, fünfmal niedriger als für die 2S-4P-Messung. Dies entspricht einer Unterdrückung der Dopplerverschiebung um sechs Größenordnungen. Bei dieser Präzision wird die Lichtkraftverschiebung durch die Beugung der Atome am optischen Gitter, welches durch die gegenläufigen Laserstrahlen erzeugt wird, signifikant. Diese Lichtkraftverschiebung wurde zum ersten Mal für die 2S-nP-Übergänge beobachtet und konnte durch ein hierfür entwickeltes Modell gut beschrieben werden. Die Größe aller anderen systematischen Effekte, mit Ausnahme der sehr genau bekannten Rückstoßverschiebung, wird mit jeweils kleiner als 500 Hz abgeschätzt. Die blinde Datenanalyse ist zum Zeitpunkt des Verfassens dieser Arbeit noch im Gange, weshalb noch keine Übergangsfrequenzen angegeben werden können. Die vorläufige Analyse lässt jedoch eine fünffache Verbesserung der Bestimmung der Rydberg-Konstante und des Protonenladungsradius im Vergleich zur 2S-4P-Messung und eine zweifache Verbesserung im Vergleich zur momentan präzisesten Bestimmung an atomarem Wasserstoff erwarten. Damit liegt die Unsicherheit auf den bestimmten Wert des Protonenladungsradius innerhalb eines Faktors fünf der Unsicherheit des myonischen Wertes. Die 2S-6P-Messung ist zentraler Gegenstand dieser Arbeit.Precision spectroscopy of atomic hydrogen is an important way to test bound-state quantum electrodynamics (QED), one of the building blocks of the Standard Model. In its simplest form, such a test consists of the comparison of a measured transition frequency with its QED prediction, which can be calculated with very high precision for the hydrogen atom. However, these calculations require some input in the form of physical constants, such as the Rydberg constant and the proton charge radius, both of which are currently determined to a large degree by hydrogen spectroscopy itself. Therefore, the frequency of at least three different transitions needs to be measured in order to test QED. Equivalently, a comparison of the values of the Rydberg constant and the proton charge radius determined from measurements of different transitions constitutes a test of QED. To this end, laser spectroscopy of optical 2S-nP transitions has been performed in this work. As these transitions are one-photon transitions, they are affected by a different set of systematic effects than the two-photon transitions on which most other spectroscopic measurements of hydrogen are based. In order to contribute to the test of QED, their transition frequencies must be determined with a relative uncertainty on the order of one part in 10^12, corresponding to approximately 1 kHz in absolute terms. This is in turn approximately a factor of 10000 smaller than the relatively broad natural linewidth of the 2S-nP transitions, and a successful measurement requires both a very large experimental signal-to-noise ratio and a detailed theoretical understanding of the line shape of the observed resonance. The 2S-nP transitions were probed on a cryogenic beam of hydrogen atoms, which were optically excited to the metastable 2S level. The atomic beam was crossed at right angles with counter-propagating spectroscopy laser beams, which further excited the atoms to the nP level. The fluorescence from the subsequent rapid spontaneous decay served as experimental signal. The excitation with two counter-propagating beams lead to two Doppler shifts of equal magnitude, but opposite sign, which thus canceled each other out. A velocity-resolved detection was used to determine any residual Doppler shifts, which could be excluded within the measurement uncertainty for both of the measurements discussed below. In a first experiment, the 2S-4P transition was probed. Quantum interference of neighboring atomic resonances produced subtle distortions of the line shape, which were found to be significant because of the very large resolution relative to the linewidth. The line shifts caused by the distortions were directly observed and could be removed by use of a line shape model based on perturbative calculations. With this, the transition frequency was determined with a relative uncertainty of 4 parts in 10^12. In combination with the very precisely measured 1S-2S transition frequency, this allowed the, at the time, most precise determination of the Rydberg constant and the proton charge radius from atomic hydrogen. Moreover, good agreement was found with the much more precise value of the proton charge radius extracted from spectroscopy of muonic hydrogen, which had been in significant disagreement with previous data from (electronic) hydrogen, causing concern about the validity of QED. This result has since been confirmed by other experiments. The 2S-4P measurement is treated in the appendix of this thesis. The 2S-4P measurement, despite its large signal-to-noise ratio, was limited by counting statistics. To improve precision, a transition with a narrower linewidth and an improved experimental signal was necessary. Hence, the study of the 2S-6P transition, which offers a three times smaller natural linewidth, was begun. The atomic beam apparatus was upgraded, resulting in a corresponding decrease of the experimentally observed linewidth, and a close to an order of magnitude larger flux of atoms in the low-velocity tail of the atomic beam. Together with a detector redesign, this led to an up to 16 times larger signal than for the 2S-4P measurement, opening the path to increased precision. The Doppler-shift suppression was also rebuilt to support such precision, including a fiber collimator developed for this purpose, which provides high-quality spectroscopy beams at the new transition wavelength of 410 nm. This enabled a measurement of the 2S-6P transition frequency with a statistical uncertainty of 430 Hz, five times lower than for the 2S-4P measurement and corresponding to a suppression of the Doppler shift by six orders of magnitude. At this level of precision, the light force shift from the diffraction of atoms at the light grating formed by the counter-propagating spectroscopy beams becomes significant. This light force shift was directly observed for the first time for the 2S-nP transitions and found to be well-described by a model derived for this purpose. The size of all other systematic effects, except the very precisely known recoil shift, is estimated to be below 500 Hz each. The blind data analysis is ongoing at the time of writing and thus no transition frequencies can yet be given. However, a preliminary analysis suggests a five-fold improvement in the determination of the Rydberg constant and the proton charge radius as compared to the 2S-4P measurement, and a two-fold improvement over the currently most precise determination from atomic hydrogen. This places the uncertainty of the determined value of the proton charge radius within a factor of five of that of the muonic value. The 2S-6P measurement is treated in the main text of this thesis