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Coherent Diffractive Imaging (CDI) has become an increasingly popular frame work in which to solve the classic phase problem in imaging due to benefits in resolution and the facility of collecting data in this modality. In particular, there is considerable interest in using the short wavelength and high coherence of fourth generation x-ray sources with CDI techniques to phase non-crystalline, or nano-crystalline biomolecular samples. CDI provides an opportunity to determine the structure of proteins and other biological samples which are unable to be phased with the standard techniques of protein crystallography, typically due to lack of adequate crystalline samples. Methods of non-crystalline phase retrieval are legion, however many suffer from limitations in resolution or the inability to recover phase fields containing a pathological singularity. Wavefields containing phase singularities are common in optical fields. The creation of an x-ray wavefield containing a pathological phase singularity is demonstrated. In this thesis a form of CDI termed astigmatic diffraction is presented, that is able tophase uniquely this class of wavefield. This is achieved by illuminating the sample with beams containing known phase curvature. The theory of the method and simulations of its application to a nano-crystalline biomolecule are presented. The experimental recovery of the direction of the phase gradient of a sample illuminated with coherent x-rays produced by a synchrotron source is shown to verify this method.

Thesis (Ph.D.)--Tufts University, 2004. / Adviser: Lawrence H. Ford. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 154-155). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D) -- Australian National University, 2005.

Thesis (Ph.D.)--Physics, Georgia Institute of Technology, 2008. / Committee Chair: Eric A. Carlen; Committee Member: Jean Bellissard; Committee Member: Michael Loss; Committee Member: Predrag Cvitanovic.

Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008. / Turgay Uzer, Committee Chair ; M. Raymond Flannery, Committee Member ; Chandra Raman, Committee Member ; Dragomir Davidovic, Committee Member ; Chongchun Zeng, Committee Member.

The advent of highly-coherent x-ray light sources, such as those now available world-wide in modern third-generation synchrotrons and increasingly available in free-electron lasers, is driving the need for improved analytical and experimental techniques which exploit the coherency of the generated light. As the light illuminating a sample approaches full coherence, a simple Fourier transform describes the diffraction pattern generated by the scattered light in the far field; because the Fourier transform of an object is unique, coherent scattering can directly probe local structure in the scattering object instead of bulk properties. In this dissertation, we exploit the coherence of Advanced Light Source beamline 12.0.2 to build three types of novel coherent scattering microscopes. First, we extend the techniques of coherent diffractive imaging and Fourier transform holography, which uses iterative computational methods to invert oversampled coherent speckle patterns, into reflection geometry. This proof-of-principle experiment demonstrates a method by which reflection Bragg peaks, such as those from the orbitally-ordered phase of complex metal oxides, might eventually be imaged. Second, we apply a similar imaging method to the x-ray beam itself to directly image the mutual coherence function with only a single diffraction pattern. This technique supersedes the double-slit experiments commonly seen in the scattering literature to measure the mutual intensity function by using a set of apertures which effectively contains all possible double slit geometries. Third, we show how to evaluate the speckle patterns taken from a labyrinthine domain pattern for "hidden" rotational symmetries. For this measurement, we modify the iterative algorithms used to invert speckle patterns to generate a large number of domain configurations with the same incoherent scattering profile as the candidate pattern and then use these simulations as the basis for a statistical inference of the degree of ordering in the domain configuration. We propose extending this measurement to position-resolved speckle patterns, creating a symmetry-sensitive microscope. The three new techniques described herein may be employed at current and future light sources.

abstract: The central purpose of this work is to investigate the large-scale, coherent structures that exist in turbulent Rayleigh-Bénard convection (RBC) when the domain is large enough for the classical ”wind of turbulence” to break down. The study exclusively focuses on the structures that from when the RBC geometry is a cylinder. A series of visualization studies, Fourier analysis and proper orthogonal decomposition are employed to qualitatively and quantitatively inspect the large-scale structures’ length and time scales, spatial organization, and dynamic properties. The data in this study is generated by direct numerical simulation to resolve all the scales of turbulence in a 6.3 aspect-ratio cylinder at a Rayleigh number of 9.6 × 107 and Prandtl number of 6.7. Single and double point statistics are compared against experiments and several resolution criteria are examined to verify that the simulation has enough spatial and temporal resolution to adequately represent the physical system. Large-scale structures are found to organize as roll-cells aligned along the cell’s side walls, with rays of vorticity pointing toward the core of the cell. Two different large- scale organizations are observed and these patterns are well described spatially and energetically by azimuthal Fourier modes with frequencies of 2 and 3. These Fourier modes are shown to be dominant throughout the entire domain, and are found to be the primary source for radial inhomogeneity by inspection of the energy spectra. The precision with which the azimuthal Fourier modes describe these large-scale structures shows that these structures influence a large range of length scales. Conversely, the smaller scale structures are found to be more sensitive to radial position within the Fourier modes showing a strong dependence on physical length scales. Dynamics in the large-scale structures are observed including a transition in the global pattern followed by a net rotation about the central axis. The transition takes place over 10 eddy-turnover times and the subsequent rotation occurs at a rate of approximately 1.1 degrees per eddy-turnover. These time-scales are of the same order of magnitude as those seen in lower aspect-ratio RBC for similar events and suggests a similarity in dynamic events across different aspect-ratios. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

Coherent communication systems became practical with the advent of integrated electronic circuits capable of supporting Digital Signal Processing (DSP) at speeds compatible with line rates. Much of the complexity and expense of the functions required in a coherent receiver to compensate for optical channel uncertainties and impairments could be transferred to DSP algorithms. The aim of the research presented in this thesis is to develop radical breakthrough DSP algorithms and design new architectures for the digital coherent optical receiver within the RF-Cité system and optical fiber network supported distributed millimeter wave wireless antenna system. The model of an optical channel is fundamental for understanding phase and polarization drift, chromatic dispersion, polarization mode dispersion and other drawbacks of the fiber optic systems in order for the signal processing algorithm to compensate these effects. In this thesis firstly an evaluation of the optical channel model that accurately describes the single mode fiber as a coherent transmission medium is reviewed through analytical, numerical and experimental analysis. Secondly, an original approach to the design of a digital coherent optical receiver is proposed which can adapt to random time-varying state of polarization (SOP) for both the local oscillator and signal. To address the problem, two different methods of polarization diverse recovery of the modulation with carrier phase estimation and elimination of sign ambiguity are performed and verified by numerical simulations. The results show the accurate recovery of the modulation and error-free constellation demodulation. Furthermore, inspired by former investigations, the theoretical analysis of a novel microwave photonic integrated circuit (MPIC) implementations of various building blocks used within the RF-Cité architecture is presented. The application of the proposed circuit in RoF systems is demonstrated by computer simulations using the Virtual Photonics Inc. software and OptiSuite packages. The performance of the proposed MPIC in a RoF system is assessed through advance modulation format techniques that have been employed in many wireless communication standards owing to their high spectral efficiency. In the DSP module, delay compensation is applied to synchronize the received signal, and the system performance is evaluated by measuring the error vector magnitude of the received signal using single-mode fiber. This scheme removes the temperature control requirement; an undesirable feature in terms of energy consumption considerations. Also, a modified polarization demultiplexing algorithm is employed to classify the input polarizations that transmit two independent channels that are mixed randomly as the light is propagating in the optical fiber. This novel technique enables blind algorithms to accurately track polarization channel alignment, through achieving accurate polarization de-multiplexing obtained by numerical simulations and experiments.

Speckles are a phenomenon which often appears in situations involving lasers. Their properties can be used as an advantage but in the case of LiDAR applications, they’re purelydestructive. The peaks and troughs of the intensity distribution across the collimatinglens can be seen as variations in signal strength at the detector. The project presented inthis paper examines the properties of these intensity patterns and how their various sizeseffects the sampled signal. This is done by experimental measurements with the use ofa coherent LiDAR accompanied by a simulation to recreate and explain the behavioursof the results obtained in the measurements. The study shows a simulation which exclusively takes speckle dependence into account successfully produce similar results asphysical experiments. The varying of subjective speckle sizes on the detector was foundto have little effect on the sampled signal quality, though the improved averaging of thesmaller speckles caused the signal strength to shift in tranquil manner.