In the search for natural orbital angular momentum (OAM) effects, some of the first incoherent scatter experiments with twisted radar beams during aurora were conducted at Poker Flat Incoherent Scatter Radar (PFISR), Alaska, USA, in October 2012. Experimental data of scatter from beam configurations with opposite twists were investigated. By the use of hypothesis tests in combination with Monte Carlo simulations together with traditional estimations of the mean and confidence interval, asymmetries between scatter of radar beams with opposite twists were identified for an integration time of at least 30 minutes. Asymmetries were detected in the internal radar noise too, but not necessarily with the same signs as for the asymmetries from the ionospheric signals. The asymmetries identified could be due to amplified noise for signals coming from intense aurora or perhaps the rectangular-shaped antenna array used at PFISR. These two possible causes need to be ruled out before suggesting that the asymmetries identified are an outcome of OAM effects present in the ionosphere.

The aim of this research is to develop a method for expanding the Jost functions as a Taylor-type power series on the complex angular momentum plane. From this method in conjunction with the Watson transformation, we were able to express the scattering amplitude as a sum of the background and pole terms, furthermore, this method propose a way of evaluating, numerically, the pole term. To demonstrate how this method may be applied, we considered the Born approximation. We found out that the developed method improved the Born approximation at large scattering angles. Therefore, this method is useful when the di fferential cross section of the background term fails to converge to that of the exact diff erential cross section at large scattering angles. / Dissertation (MSc)--University of Pretoria, 2016. / National Research Foundation (NRF) / Physics / MSc

The inverse eigenvalue problem for a given operator is to determine the coefficients by using knowledge of its eigenfunctions and eigenvalues. These are determined by the behavior of the solutions on the domain boundaries. In our problem, the Schrödinger operator acting on functions defined on the unit ball of $\mathbb{R}^3$ has a radial potential taken from $L^2_{\mathbb{R}}[0,1].$ Hence the set of the eigenvalues of this problem is the union of the eigenvalues of infinitely many Sturm-Liouville operators on $[0,1]$ with the Dirichlet boundary conditions. Each Sturm-Liouville operator corresponds to an angular momentum $l =0,1,2....$. In this research we focus on the uniqueness property. This is, if two potentials $p,q \in L^2_{\mathbb{R}}[0,1]$ have the same set of eigenvalues then $p=q.$ An early result of P\"oschel and Trubowitz is that the uniqueness of the potential holds when the potentials are restricted to the subspace of the even functions of $L_{\mathbb{R}}^2[0,1]$ in the $l=0$ case. Similarly when $l=0$, by using their method we proved that two potentials $p,q \in L^2_{\mathbb{R}}[0,1]$ are equal if their even extension on $[-1,1]$ have the same eigenvalues. Also we expect to prove the uniqueness if $p$ and $q$ have the same eigenvalues for finitely many $l.$ For this idea we handle the problem by focusing on some geometric properties of the isospectral sets and trying to use these properties to prove the uniqueness of the radial potential by using finitely many of the angular momentum.

Le moment angulaire est une quantité essentielle pour l'étude d'objets en interaction. Tout comme la matière, un rayonnement porte du moment angulaire. Il se décompose en deux composantes, moment angulaire de spin (MAS) et moment angulaire orbital (MAO). Chacune de ces composantes a des propriétés spécifiques et ont donné lieu à de nombreuses applications en utilisant de la lumière dans le domaine visible et infrarouge. Dans cette thèse, nous nous proposons d'étudier le comportement des deux types de moment angulaire de la lumière dans un processus très non-linéaire appelé génération d'harmoniques d'ordre élevé (GHOE). Dans ce processus physique connu depuis 1987, un laser infrarouge intense est focalisé dans un jet d'atomes ou de molécules, ce qui dans le bon régime d'intensité permet de générer un rayonnement à courte longueur d'onde (domaine extrême ultraviolet) et extrêmement bref (attoseconde, 1 as = 10⁻¹⁸ s). Nous commençons par décrire théoriquement ce processus, ainsi que définir de manière approfondie la notion de moment angulaire de la lumière. Nous étudions ensuite la GHOE à partir d'un faisceau infrarouge portant du MAO, ce qui nous permet d'obtenir une source unique, générant des impulsions lumineuses ultrabrève de moment angulaire orbital contrôlé et de longueur d'onde de l'ordre de 10nm. Nous étudions étudions la GHOE à partir de faisceaux portant du MAS. En utilisant une résonance du gaz de génération, nous parvenons à transmettre ce moment angulaire au rayonnement extrême ultraviolet. Ce rayonnement est ensuite utilisé pour mesurer des dichroïsmes circulaires de photoionisation dans des molécules chirales, mesures auparavant réservées aux sources synchrotrons. Ceci ouvre la voie à des mesures chirotpiques résolues en temps à l'échelle femto/attoseconde. / Angular momentum is an ubiquitous quantity in all areas of physics. Just like matter, radiation carries angular momentum. It can be decomposed in two parts, namely the spin angular momentum (SAM) and the orbital angular momentum (OAM). Each one of these components has very specific properties and lead to numerous applications using visible and infrared light. In this thesis, we study the behavior of these two types of light angular momentum in a very non-linear process called high harmonic generation (HHG). In this physical process known since 1987, an intense infrared laser is focused into an atomic or molecular gas jet, which in the right intensity regime allows to generate a radiation which has a short wavelength (extreme ultraviolet domain) and is extremely brief (attosecond, 1 as = 10⁻¹⁸ s).We begin by describing theoretically this process, as well as defining in depth the notion of light angular momentum. We then study HHG from an infrared laser carrying OAM. This allows to obtain an unique light source, generating ultrashort light pulses of controlled orbital angular momentum with a wavelength of the order of 10 nm. We then study GHOE from beams carrying MAS. Using a resonance from the generation gas, we manage to transfer this angular momentum to the emitted extreme ultraviolet radiation. This radiation is finally used to measure photoionisation circular dichroisms in chiral molecules, measurements previously restricted to synchrotron sources. This paves the way towards chiroptic time resolved measurement on a femto/attosecond timescale.

A galaxy's angular momentum is known to be correlated with its morphology: at a given mass, spiral galaxies have higher angular momenta than elliptical galaxies. A galaxy's angular momentum is also largely set by its formation history: in particular, how much gas and the kinematic state of the gas that both accretes onto it and is expelled in galactic outflows from AGN and supernovae. All gas inflowing to and outflowing from the galaxy interacts with gas in the region surrounding the galaxy called the circumgalactic medium (CGM), which means at a fundamental level, the CGM controls the angular momentum of the galaxy. Therefore, to really understand the origins of galactic angular momentum, it is necessary to understand the angular momentum of the CGM itself. In this dissertation, I present a series of projects aimed at studying angular momentum in the CGM using the Illustris and IllustrisTNG cosmological hydrodynamical simulations suites. In an appendix, I also present a project on searching a survey of neutral hydrogen for previously undetected ultra-faint dwarf galaxies in and around the Milky Way's CGM. First, to understand how present-day galaxies acquire their observed angular momentum, I analyze the evolution of the angular momentum of Lagrangian gas mass elements as they accrete onto dark matter halos, condense into Milky Way-scale galaxies, and join the z=0 stellar phase of those galaxies. I find that physical feedback from the galaxy is essential in order to produce reasonable values of galactic angular momentum, and that most of the effects of this feedback occur in the CGM, necessitating studying the angular momentum of the CGM itself. Following on from this result, I then characterize the angular momentum distribution and structure within the CGM of simulated galaxies over a much larger range of halo masses and redshifts, with the goal of determining if there are common angular momentum properties in CGM populations. I indeed find that the angular momentum of the CGM is larger and better aligned around disk galaxies that themselves have high angular momentum. I also identify rotating structures of cold gas that are generally present around galactic disks. This clear connection of the CGM to the galaxy motivated a detailed comparison to observations of cold CGM gas. I perform this comparison in the following chapter where I use the highest-resolution simulation from the IllustrisTNG suite of cosmological magneto-hydrodynamical simulations to generate synthetic observations of cold CGM gas around star-forming galaxies in order to study kinematics and compare them to line-of-sight observations of cold gas near comparable galaxies. With this direct comparison to observations of the CGM, I show that IllustrisTNG produces rotating CGM gas consistent with observations to a high degree. In the penultimate chapter I present unpublished work where I begin to examine angular momentum evolution in the CGM on much finer timescales than can be resolved with the cosmological simulations I have used thus far. Preliminary results suggest that gas can experience large changes in angular momentum very quickly, and that these changes may be connected to corresponding changes in the temperature of the gas. Finally, I conclude by summarizing my main results and briefly discussing what questions still remain unanswered and my plans and strategies for pursuing these questions in my future work.

The objective of this work is to develop a near-infrared laser device capable of emitting orbital angular momentum (OAM) light. The prototyped device must be suitable for compact, energy-saving optical communication applications. Integrated OAM lasers will revolutionize high-capacity data transmission over any telecommuni- cation network environment, as OAM light can be guided and transmitted through kilometers of optical fibers and propagated in free space and underwater. Several methods for generating OAM light employing various complex monolithic and hybrid integration methods have been demonstrated. In this work, microscale integrated spiral phase plates (SPPs) are chosen to convert the laser beam output into an OAM mode. The concept and design fundamentals of SPPs are discussed, followed by the SPP fabrication process and their implementation in a high-speed communication setup and then integration with a semiconductor laser. SPPs are fabricated by a novel direct laser writing that provides the possibility to rapidly prototype 3D photonic structures via a two-photon polymerization pro- cess. After fabrication, SPPs are used in a fine-tuned free-space optical experimental setup that requires high-precision intercomponent alignment to test the high-speed OAM communication system and analyze the quality of OAM modes, resulting in high-purity OAM signals at data rates up to 1.8 Gbit/s – limited by the avalanche photodetector (APD) frequency response. The fabricated 20-μm-diameter SPPs were the smallest reported in the literature to date for optical characterization. A proof-of-concept monolithic light-emitting array, as a highly integrated OAM laser source, is further proposed for telecommunications and other applications. SPP-integrated 940-nm vertical-cavity surface-emitting laser (VCSEL) array chips that are relatively low-cost, have a small footprint, and are manufacturable in high volumes are developed. SPPs with topological charge modulus values from 1 to 3 are fabricated on the VCSEL arrays, demonstrating OAM modal purities up to ∼65%. The experimentally evaluated data rates in the OAM setup showed consistently sta- ble links up to 2.0 Gbit/s with a bit error ratio of ∼ 1.6 × 10−8 (APD-limited). The challenges of SPP-laser integration are summarized, with the conclusion that the widespread adoption of OAM is limited by the availability of practical integrated solutions for OAM generation and detection.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1982. / Microfiche copy available in Archives and Science. / Bibliography: leaves 75-77. / by John Roberts Anderson. / M.S.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第17770号 / 理博第3893号 / 新制||理||1561(附属図書館) / 30577 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 青山 秀明, 教授 畑 浩之, 准教授 早田 次郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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