Orbital angular momentum (OAM) is a property of light that is widely used for applications in bioimaging, optical communication and optical manipulation, but is mainly limited to the infrared and visible spectra. Developing a table-top source of Extreme Ultraviolet (XUV) light containing an arbitrary amount of OAM is yet to be achieved. We accomplish this by exploiting high-harmonic generation (HHG), a process whereby an infrared pump beam produces high order harmonics. We experimentally demonstrate the conservation of OAM in HHG by measuring harmonics of order n containing n times the OAM of the pump (n = 11, 13, 15 in our experiment). These results agree with our theoretical model. We also show theoretically how to manipulate the HHG process to impart an arbitrary amount of OAM to the di fferent harmonics. We hence show the way to a table-top and flexible source of XUV light containing orbital angular momentum.

Orbital angular momentum (OAM) is a property of light that is widely used for applications in bioimaging, optical communication and optical manipulation, but is mainly limited to the infrared and visible spectra. Developing a table-top source of Extreme Ultraviolet (XUV) light containing an arbitrary amount of OAM is yet to be achieved. We accomplish this by exploiting high-harmonic generation (HHG), a process whereby an infrared pump beam produces high order harmonics. We experimentally demonstrate the conservation of OAM in HHG by measuring harmonics of order n containing n times the OAM of the pump (n = 11, 13, 15 in our experiment). These results agree with our theoretical model. We also show theoretically how to manipulate the HHG process to impart an arbitrary amount of OAM to the di fferent harmonics. We hence show the way to a table-top and flexible source of XUV light containing orbital angular momentum.

The electron microscope is an ideal tool to prepare an electron into a specified quantum state, entangle that state with states in a specimen of interest, and measure the electron final state to indirectly gain information about the specimen. There currently exist excellent technologies to prepare both momentum eigenstates (transmission electron microscopy) and position eigenstates (scanning transmission electron microscopy) in a narrow band of energy eigenstates. Similarly, measurement of the momentum and position final states is straightforward with post-specimen lenses and pixelated detectors. Measurement of final energy eigenstates is possible with magnetic electron energy loss spectrometers. In 2010 and 2011, several groups independently showed that it was straightforward to prepare electrons into orbital angular momentum eigenstates. This disseratation represents my contributions to the toolset we have to control these eigenstates: preparation, application (interaction with specimen states), and measurement. My collaborators and I showed that phase diffraction gratings efficiently produce electron orbital angular momentum eigenstates; that control of orbital angular momentum can be used to probe chirality and local magnetic fields; and that there are several routes toward efficient measurement.

Studying the orbital angular momentum (OAM) of light has become rather fashion- able in the 21st century. Yet, most of major advances in OAM related research have been conducted in the visible regime of light. A significant portion OAM research revolves around using OAM radiation to perform some function that is deemed useful. Examples of this are optical trapping, micro-machine manipulation and the development of advanced communication systems. Photon entanglement measurements also make use of OAM radiation. Interest in probing radiation for naturally generated OAM is far less popular. For example, interest in building OAM sensitive telescopes was sparse at the beginning of this thesis, however the first reported detection of astrophysical OAM was published in 2013. This thesis aims to tackle these two areas of sparse research by developing the components and understanding in order to build OAM sensitive millimetre-wavelength telescopes. Spiral phase plates (SPPs) are the device of choice. The majority of the thesis sets out to test three different SPPs, in order to compare and contrast different methods for their manufacture and design. Electromagnetic theory of OAM and its generation is reviewed first. Then, each SPP is modelled numerically fol- lowed by in-depth modelling of each plate by using the computational electromagnetic package FEKO. Finally, each plate is measured with a three dimensional field scanner developed as part of this thesis. Development of a new modular SPP design concludes this thesis.

Twenty-odd years ago, scientists managed to produce several new techniques for manipulating certain properties of laser and microwave radiation. These new properties made it possible for the radiation to contain a lot more information than what was previously known. What they had discovered was that light could be twisted, thereby not only carrying polarization, also known as spin angular momentum (SAM) but also orbital angular momentum (OAM).Radar beams are used by scientists to probe the earth’s ionosphere. By measuring the echo of the radar waves one can deduce a lot of information, such as density and temperature of the plasma. In this thesis we will expand an existing program (iscatspb0.m) which computes the spectrum of plasma fluctuations as seen with an incoherent scatter radar, to having it incorporate radar beams carrying OAM, to see what new information of the plasma can be obtained.The three major findings in this thesis were what magnitude of the integer l is needed in order for the contribution of OAM to equal the contribution for the beam opening angle, how much the radar beam opening angle affected the measurements and in what way the spectrum obtained by a twisted beam is affected by different flows

Twisted particles carry Orbital Angular Momentum (OAM), an important property utilized to encode quantum information. The OAM of twisted photons can be trans- ferred onto condensed matter systems in the form of twisted excitons. Numerical solutions of the time-dependent Schr ̈odinger equation for a 3-arm molecular chain are used to demonstrate the manipulation of twisted excitons via an external magnetic field. We present the first design for an OAM transistor in a quasi-1D system that can be used to control the flow of OAM using the magnetic field. The underlying mechanism is the interaction between OAM and the magnetic field which leads to a orbit-resolved Bloch oscillation (ORBO). We present the semi-classical equations of motion for this phenomenon in a one-dimensional system. Unlike classical Bloch oscil- lation, an important effect in ultrafast electron dynamics, the magnet driven ORBO is not limited by electrical breakdown and can easily be observed in natural solids.

Thesis (PhD)--Stellenbosch University, 2015.

Free-Space Optical (FSO) communication through the terrestrial atmospheric channel offers many benefits in the wireless communications arena, like power efficiency; suitability for secure communications; absence of electromagnetic interference; and potentially very high bandwidth. An optical beam propagating through the atmosphere is subject to optical turbulence. Optical turbulence is a random process that distorts the intensity and phase structure of a propagating optical beam and induces a varying signal at the receiver of an FSO communication link. This phenomenon (usually referred to as scintillation) degrades the performance of the FSO link by increasing the probability of error. In this dissertation we seek to characterize the effects of the scintillation-induced power fluctuations by determining the channel capacity of the optical link using numerical methods. We find that capacity decreases monotonically with increasing turbulence strength in weak turbulence conditions, but it is non-monotonic in strong turbulence conditions. We show that low-density parity-check (LDPC) codes provide strong error control capabilities in this channel if a perfect interleaver is used. Multiple transmit optical beams can be used to reduce scintillation. We characterize the spatial correlation of the atmospheric optical channel and determine a scintillation model for the multiple-beam scheme. With this model we can predict the effective reduction in scintillation as a function of the system design parameters. A Multi-channel FSO communications system based on orbital angular momentum (OAM)-carrying beams is studied. We analyze the effects of turbulence on the system and find that turbulence induces attenuation and crosstalk among OAM channels. Based on a model in which the constituent channels are binary symmetric and crosstalk is a Gaussian noise source, we find optimal sets of OAM states at each turbulence condition studied, and determine the aggregate capacity of the multi-channel system at those conditions. At very high data rates the FSO channel shows inter-symbol interference (ISI). We address the problem of joint sequence detection in ISI channels and decoding of LDPC codes. We derive the belief propagation equations that allow the simultaneous detection and decoding of a LDPC codeword in a ISI channel.

Final accepted manuscripts of parts 4 and 5 from Roadmap on Structured Light, authored by Masud Mansuripur, College of Optical Sciences, The University of Arizona.

We investigate two medium-facilitated interactions between properties of light upon propagation through optical fiber. The first is interaction between the spin and intrinsic orbital angular momentum in a linear optical medium. This interaction gives rise to fine structure in the longitudinal momenta of fiber modes and manifests in rotational beating effects. We probe those beating effects experimentally in cutback experiments, where small segments are cut from the output of a fiber to probe the evolution of both output polarization and spatial orientation, and find agreement between theoretical predictions and measured behavior. The second is nonlinear optical interaction due to cross- and self-phase modulation between the complex-valued temporal amplitude profile of pump pulses and the amplitude profiles of generated signal and idler pulses in optical fiber photon-pair sources utilizing the four-wave mixing process named modulation instability. We develop a model including the effects of these nonlinear phase modulations (NPM) describing the time-domain wave function of the output biphoton in the low-gain regime. Assuming Gaussian temporal amplitude profiles for the pump pulse, we numerically simulate the structure of the biphoton wave function, in symmetric and asymmetric group velocity matching configurations. Comparing the overlap of the joint temporal amplitudes with and without NPM indicates how good of an approximation neglecting NPM is, and we investigate the effects of NPM on the Schmidt modes. We find that effects of NPM are small on temporally separable sources utilizing symmetric group velocity matching, but appreciably change the state of temporally entangled sources with the same group velocity matching scheme. For sources designed to produce entangled biphotons, our simulations suggest that NPM increases the Schmidt number, which may increase entanglement resource availability with utilization of a phase-sensitive detection scheme. We find that NPM effects on temporally separable sources designed with asymmetric group velocity matching produce non-negligible changes in the state structure. The purity is unaffected at perfect asymmetric group velocity matching, but if the pump is detuned from the correct wavelength, the purity degrades. The largest changes to the state due to NPM occur in long fibers with long pulse durations and low repetition rates.