RECEIVER DESIGN AND PERFORMANCE ANALYSIS FOR FREE-SPACE OPTICAL COMMUNICATIONS

Ph.DDOCTOR OF PHILOSOPH

The design and testing of a novel compact real-time hybrid Compton and neutron scattering instrument.

The requirement for multiple-purpose imaging system occurs regularly within the field of radioactive materials safeguard and security applications. Current instrumentation utilised within the field of dual gamma-ray and neutron imaging systems suffer with limited portability, long scan times, and cover limited energy ranges. Conversely, the imaging system designed, built and tested in this work is not only capable of locating both gamma rays and neutrons, but is also capable of operating in near real time, covers a large energy range and is portable to a desktop degree. The imaging concept applied simultaneously combines Compton and neutron scattering techniques within a threelayer design comprising of a unique combination of scintillators backed with pixelated arrays of photodetectors in the form of 8 x 8 Silicon Photomultipliers (SiPMs). The system features the organic scintillator EJ-204, neutron sensitive lithium glass and thallium doped caesium iodide utilised along with associated SiPMs and front-end electronics, all enclosed within a volume of 120 mm x 120 mm x 200 mm. Further backend electronics is situated within a separate unit where each of the data channels are simultaneously interrogated in order to determine the location of the incident gamma rays and neutrons. The validity of the instrument has been computationally verified using MCNP6 and Geant4 Monte Carlo simulation codes and experimentally tested using Cs-137 gamma sources of ~300 kBq and a Cf-252 neutron source featuring an emission rate of 106 neutrons per second. The developed instrument offers a real-time response with a scan time of 60 seconds and a further data analysis time of 60 seconds. The intrinsic efficiency of the instrument has been experimentally measured to be in the order of 10-4 for both gamma rays at 0.667 MeV and fast neutrons at average energy of 2.1 MeV, and 0.78 for thermal neutron

PREDICTION AND CONTROL OF IMAGE PROPERTIES IN ADVANCED COMPUTED TOMOGRAPHY

Computed Tomography (CT) is an important technique that is in widespread use for disease diagnosis, monitoring, and interventional procedures. There are many varieties of CT including cone-beam CT (CBCT) that has exceptional high spatial resolution and spectral CT that incorporates energy-dependent measurements for advanced material discrimination. The goal of this research is to quantify image properties using a prospective prediction framework for advanced reconstruction in CBCT and spectral CT systems. These predictors analyze the dependencies of image properties on system configuration, acquisition strategy, and reconstruction regularization design. The prospective estimation of image properties facilitates novel system and acquisition design, adaptive and task-driven imaging, and tuning of regularization for robust and reliable performance. The proposed research quantifies the image properties of model-based iterative reconstruction (MBIR) in CBCT and model-based material decomposition (MBMD) in spectral CT, including spatial resolution, the generalized response to local perturbations, and noise correlation. Predictions are derived with a realistic system model including physical blur, noise correlation, and a poly-energetic model that applies to a variety of spectral CT protocols. Reconstruction methods combining data statistical fidelity and various advanced regularization designs are explored. Prediction accuracy is validated with measured image properties in both simulation and physical experiments. The theoretical understanding is applied to applications with prospective reconstruction regularization design

Development of radiation transport techniques for modelling a high-resolution multi-energy photon emission tomography system

”Nondestructive characterization techniques such as gamma tomography represent powerful tools for the analysis and quantification of physical defects and radionuclide concentrations within nuclear fuel forms. Gamma emission tomography, in particular, has the ability to utilize the inherent radiation within spent nuclear fuel to provide users with information about the migration and concentration of fission and activation products within the fuel form. Idaho National Laboratory is interested in using this technology to analyze new nuclear fuel forms for potential use in next generation nuclear reactors. In this work, two aspect of the system are analyzed. The first is a semi-analytic radiation transport methodology in conjunction with a parallel beam collimator developed to facilitate the acquisition of data from Monte-Carlo modeling of a small submersible gamma tomography system, with a focus on emission information. The second is a pinhole collimator designed to optimize count rates, diameter, and acceptance angle to increase the sampling of the fuel forms to decrease data acquisition time. Utilizing the semi-analytical technique, computational savings of 107-1011 can be achieved with a degradation in accuracy of 1845% compared to a standard isotropic uniform Monte-Carlo N Particle transport simulation. However, this loss in accuracy can be minimized by increasing the parallel beam collimator’s aspect ratio where it tends towards a degenerate cylinder. The semianalytic technique is also compared to inbuilt acceleration techniques. The pinhole collimator design yields count rates on the order of 100s-1000s which represents a 101-102 increase in actual count rates over the entirety of the photon spectrum”--Abstract, page iv

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC

A Lunar Optical-Ultraviolet-Infrared Synthesis Array (LOUISA)

This document contains papers presented at a workshop held to consider 'optical ultraviolet infrared' interferometric observations from the moon. Part 1 is an introduction. Part 2 is a description of current and planned ground-based interferometers. Part 3 is a description of potential space-based interferometers. Part 4 addresses the potential for interferometry on the moon. Part 5 is the report of the workshop's working groups. Concluding remarks, summary, and conclusions are presented in Part 6

The Next Generation Space Telescope

In Space Science in the Twenty-First Century, the Space Science Board of the National Research Council identified high-resolution-interferometry and high-throughput instruments as the imperative new initiatives for NASA in astronomy for the two decades spanning 1995 to 2015. In the optical range, the study recommended an 8 to 16-meter space telescope, destined to be the successor of the Hubble Space Telescope (HST), and to complement the ground-based 8 to 10-meter-class telescopes presently under construction. It might seem too early to start planning for a successor to HST. In fact, we are late. The lead time for such major missions is typically 25 years, and HST has been in the making even longer with its inception dating back to the early 1960s. The maturity of space technology and a more substantial technological base may lead to a shorter time scale for the development of the Next Generation Space Telescope (NGST). Optimistically, one could therefore anticipate that NGST be flown as early as 2010. On the other hand, the planned lifetime of HST is 15 years. So, even under the best circumstances, there will be a five year gap between the end of HST and the start of NGST. The purpose of this first workshop dedicated to NGST was to survey its scientific potential and technical challenges. The three-day meeting brought together 130 astronomers and engineers from government, industry and universities. Participants explored the technologies needed for building and operating the observatory, reviewed the current status and future prospects for astronomical instrumentation, and discussed the launch and space support capabilities likely to be available in the next decade. To focus discussion, the invited speakers were asked to base their presentations on two nominal concepts, a 10-meter telescope in space in high earth orbit, and a 16-meter telescope on the moon. The workshop closed with a panel discussion focused mainly on the scientific case, siting, and the programmatic approach needed to bring NGST into being. The essential points of this panel discussion have been incorporated into a series of recommendations that represent the conclusions of the workshop. Speakers were asked to provide manuscripts of their presentation. Those received were reproduced here with only minor editorial changes. The few missing papers have been replaced by the presentation viewgraphs. The discussion that follows each speaker's paper was derived from the question and answer sheets, or if unavailable, from the tapes of the meeting. In the latter case, the editors have made every effort to faithfully represent the discussion