No description available.

Accurate single-shot visualization of laser wakefield structures can improve our fundamental understanding of plasma-based accelerators. Previously, frequency domain holography (FDH) was used to visualize weakly nonlinear sinusoidal wakes in plasmas of density n[subscript e] < 0.6 × 10¹⁹/cm³ that produced few or no relativistic electrons. Here, I address the more challenging task of visualizing highly nonlinear wakes in plasmas of density n[subscript e] ~ 1 to 3× 10¹⁹/cm³ that can produce high-quality relativistic electron beams. Nonlinear wakes were driven by 30 TW, 30 fs, 800 nm pump pulses. When bubbles formed, part of a 400 nm, co-propagating, overlapping probe pulse became trapped inside them, creating a light packet of plasma wavelength dimensions--that is, an optical "bullet"--that I reconstruct by FDH methods. As ne increased, the bullets first appeared at 0.8 × 10¹⁹/cm³, the first observation of bubble formation below the electron capture threshold. WAKE simulations confirmed bubble formation without electron capture and the trapping of optical bullets at this density. At n[subscript] >1× 10¹⁹/cm³, bullets appeared with high shot-to-shot stability together with quasi-monoenergetic relativistic electrons. I also directly observed the temporal walk-off of the optical bullet from the beam-loaded plasma bubble revealed by FDH phase shift data, providing unprecedented visualization of the electron injection and beam loading processes. There are five chapters in this thesis. Chapter 1 introduces general laser plasma- based accelerators (LPA). Chapter 2 discusses the FDH imaging technique, including the setup and reconstruction process. In 2006, Dr. N. H. Matlis used FDH to image a linear plasma wakefield. His work is also presented in Chapter 2 but with new analyses. Chapter 3, the main part of the thesis, discusses the visualization of LPAs in the bubble regime. Chapter 4 presents the concept of frequency domain tomography. Chapter 5 suggests future directions for research in FDH. / text

A new technique for optical pattern recognition with two-center recording of persistent holograms in doubly doped LiNbO₃3:Fe:Mn crystal is presented, by which the holograms are localized in separate slices along the recording medium. The localized recording method has the distinctive advantage of selective recording and erasure of the individual holograms without affecting the entire holographic recording medium. This capability enables dynamic content modification of the optical pattern recognition systems. Also, the diffraction efficiency of localized holograms is much larger than that of the normal volume multiplexed holograms. It is theoretically shown that the localized holographic correlator (LHC) outperforms the conventional volume holographic correlators in terms of crosstalk, shift invariance, and capacity. The LHC is experimentally demonstrated. Several persistent holograms are localized within separate slices as close as 33 μm apart along the crystal. The excessive diffraction efficiency of the localized holograms is employed to enhance the LHC robustness through multiplexing several holograms per pattern within individual slices of the recording medium. A holographic data storage system based on two-center holographic recording in a doubly doped LiNbO3:Fe:Mn crystal is developed with angular multiplexing capability. The associated imaging system has been optimized for the pixel matching of pixelated bit patterns generated by a spatial light modulator (SLM) through the recording medium onto a camera. The initial multiplexed holograms show promising contrast of dark and bright pixels. With the optimized imaging system of the developed holographic memory, the implementation of a dynamic read/write data storage system with localized recording is envisioned. The large diffraction efficiency of the localized holograms enables multilevel (M-ary) data coding to improve the storage density of the system.

The gauge/string correspondence provides a non-perturbative definition of string theory and hence quantum gravity in some backgrounds, making it possible to translate statements about strongly coupled quantum field theories into results about gravity. <p><p>In this thesis, we focus on the derivation of holographic backgrounds from the field theory, without using any supergravity input. Instead, we rely crucially on the addition of probe D-branes to the stack of D-branes generating the background.<p>From the field theory description of the probe branes in the presence of the background branes, one can compute an effective action for the probes (in a suitable low-energy/near-horizon limit) by integrating out the background branes. Comparing this action with the D-brane probe action in a generic supergravity background then allows to determine the holographic background dual to the considered field theory vacuum.<p><p>In the first part, the required pre-requisites of field and string theory are recalled and this strategy to derive holographic backgrounds is explained in more detail on the basic case of D3-branes in flat space probed by a small number of D-instantons.<p><p>The second part contains the original results of this thesis, obtained by applying this strategy to several specific examples. We first derive the duals to three continuous deformations (Coulomb branch, β and non-commutative deformations) of the basic case, in the limit in which the D-instantons can probe the full geometry. We then derive the enhançon mechanism in a dual to a simple N=2 quiver gauge theory by using a fractional D-instanton as a probe and exploiting recent exact results on the Coulomb branch of N=2 quivers.<p>Finally, we obtain the near-horizon D4-brane geometry by probing the D4-branes with a small number of D0-branes.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Microwave imaging finds numerous applications involving optically obscured targets. One particular area is breast cancer detection, since microwave technology promises fast low-cost image reconstruction without the use of harmful radiation typical of X-ray mammography. However, the success of microwave imaging is hindered by a critical issue, the complex nature of near-field electromagnetic scattering in tissue. To overcome this, specialized image reconstruction algorithms alongside sensitive measurement hardware are required. In this work, real-time near-field microwave imaging algorithms known as quantitative microwave holography and scattered power mapping are explored. They are experimentally demonstrated to identify potential tumor regions in tissue phantoms. Alongside this development, quality control techniques for evaluating microwave hardware are also described. Two new methods for improving the image reconstruction quality are also presented. First, a novel technique, which combines two commonly used mathematical approximations of scattering (the Born and Rytov approximations), is demonstrated yielding improved image reconstructions due to the complimentary nature of the approximations. Second, a range migration algorithm is introduced which enables near-field refocusing of a point-spread function (PSF), which is critical for algorithms that rely on measured PSFs to perform image reconstruction. / Thesis / Doctor of Philosophy (PhD) / Breast cancer remains as one of the highest causes of cancer-related deaths in women in Canada. Though X-ray mammography remains the gold standard for regular breast cancer screening, its use of harmful radiation, painful breast compression, and radiologist dependent evaluation remain as detracting factors for its use. Over the past 40 years, researchers have been exploring the use of microwave technology in place of X-ray mammography. Microwave radiation, used at power levels similar to that of a cellphone, has been demonstrated successfully in simulations of breast scans. However, in experimental evaluations with breast phantoms, the complex scattering path of the radiation through tissue complicates image reconstruction. In this thesis, methods of improving the accuracy of microwave algorithms are explored, alongside new breast phantom structures that replicate well the electrical properties of tissue. The results of this work demonstrate the flexibility of microwave imaging, and the adversities that still need to be overcome for it to begin seeing clinical use.

In this work, two distinct types of Diffractive Optical Elements (DOEs) are designed to laterally distribute the solar spectrum across multiple photovoltaic (PV) cells. Each PV cell receives a spectral band near its bandgap energy to maximize overall solar-to-electric conversion efficiency of the system. The first DOE is an off-axis volume holographic lens. Design parameters include lateral grating period and slant angle, index modulation, film thickness, and control of swelling and index modulation attenuation in the film development process. Diffraction efficiency across the holographic lens is simulated using Rigorous Coupled Wave Analysis (RCWA). A full system model is created, and non-sequential raytracing is performed. Performance is evaluated under AM 1.5 conditions and annual insolation in Tucson, AZ, and Seattle, WA. A proof-of-concept off-axis holographic lens is fabricated and its performance is measured to confirm the optical properties of this system. The second DOE is an algorithmically-designed freeform surface relief structure. The Gerchberg-Saxton design algorithm is expanded to consider multiple wavelengths, resulting in a Broadband Gerchberg-Saxton (BGS) algorithm. All design variables are evaluated in a parametric study of the algorithm. Several DOE designs are proposed for spectrum splitting, and two of these designs are fabricated and measured. Additional considerations, such as finite sampling of the discrete Fourier transform, fabrication error, and solar divergence are addressed. The dissertation will conclude with a summary of spectrum splitting performance of all proposed DOEs, as well as a comparison to ideal spectrum splitting performance and discussion of areas for improvement and future work.

Hybridizing, in general, is the approach of combining multiple technologies, materials, or designs such to mitigate the drawbacks and enhance the benefits. The result of this combination can be referred to as a hybrid. The projects described in this work concern a number of these hybrids. The collection of projects are limited to optical applications, but are otherwise enormously different. There is perhaps no better way to illustrate this breadth than their characteristic length-scale. That is, the general size of the elements being hybridized. Ten orders of magnitude lie between the smallest system described and largest systems. At the several-nanometer scale, a single component of a composite optical material. Diamond possesses a unique combination of refractive and dispersive optical properties, making it an attractive optical material. Unfortunately, the lowest cost diamond available possesses large amounts of impurities and color. In an attempt to remove the visible color from commercially available detonation-origin nanodiamond powders we developed a facile three-step cleaning process. This process and the resulting qualities of the nanodiamond are discussed. At tens to hundreds of nanometers scale, we have worked to optimize a complete composite material system; a combination of Polystyrene-b-poly (2-vinyl pyridine) (PS-b-P2VP), a block co-polymer with self-assembly properties, and controlled size iron platinum (FePt) nanoparticles. The applications in mind are magnetic field sensors, used in medical testing and physical experiments, and fiber optic isolators, used extensively in telecommunications networks. These composites exhibited commercially significant Verdet constants in room temperature Faraday rotation measurements, and possess processing benefits over the current state-of-the-art magneto-optically active materials. Several behaviors with respect to wavelength, particle loading, and primary particle size are discussed. At the micron to centimeter scale, we have designed and characterized a high-speed fiber-optic switch for telecommunications networks capable of reconfiguring 100 times faster than currently available technologies with comparable port counts. The switch is an unconventional hybrid of the micron-scale optics of single-mode fiber modes, and the centimeter scale of free-space holography. Built primarily using off-the-shelf components and a commercially available digital micro-mirror device (DMD), the switch is protocol and bit-rate agnostic, robust against random mirror failure, and provides the basic building block for a fully reconfigurable optical add drop multiplexer (ROADM).Finally, at the scale of several meters, we address a system that hybridizes two established methods for harvesting solar energy. Sunlight can be captured as electricity using photovoltaics (PV), as well as heat, often called concentrated solar power (CSP). Each approach has benefits and drawbacks which will be discussed. A system possessing the peak efficiency of PV, with the deployable storage of CSP, would most effectively meet demand around the clock. In order to combine these technologies, we have developed an approach for designing a dichroic coating to optimize performance of such a system utilizing multi-junction photovoltaic cells while diverting unused light to heat collection. Through careful design substantial improvement to system efficiencies are shown to be possible.

We investigate phase transitions in holographic models of QCD. In chapter I, we explore the effect of constant external U(1) fields on the physics of chiral symmetry breaking, as realized in the D3/D7 model. We discover that this model exhibits the phenomenon of magnetic catalysis, which is what one would expect from a weakly coupled field theory intuition. In chapter II, we continue exploring the effect of external U(1) fields but now on the backreacted D3/D7 model, where the backreaction is obtained via a smearing procedure. We again find the magnetic catalysis effect, however the results differ from the previous case depending on the backreaction parameters. In chapter III, we investigate lattices of instantons in the D4/D8 model of chiral symmetry breaking. These instanton lattices can change dimensionality, and in particular we investigate the 1D [right arrow] 2D transition as a simpler case of the more complicated 3D [right arrow] 4D transition which is conjectured to be holographically dual to the baryonic to quarkyonic phase transition. Besides this interpretation, one could also view this as a hypothetical condensed matter system. We have a lattice of instantons dominated by two-body forces, whose interactions depend not only on their mutual distance in physical space but also on their relative orientations in the internal isospace. We obtain a rich variety of instanton crystals whose description could serve to be useful beyond holography. / text

No description available.

This dissertation is comprised of two separate topics within the domain of polarization optical engineering. The first topic is a Mueller matrix roots decomposition, and the second topic is polarization computer generated holography. The first four chapters of the dissertation are on the topic of the Mueller matrix roots decomposition. Recently, an order-independent Mueller matrix decomposition was proposed in an effort to organize the nine depolarization degrees of freedom. Chapter 1 discusses relevant Mueller matrix decomposition prior art and the motivation for this work. In chapter 2, the critical computational issues involved in applying this Mueller matrix roots decomposition are addressed, along with a review of the principal root and common methods for its calculation. The choice of the pth root is optimized at p = 10⁵, and computational techniques are proposed which allow singular Mueller matrices and Mueller matrices with a half-wave of retardance to be evaluated with the matrix roots decomposition. A matrix roots algorithm is provided which incorporates these computational results. In chapter 3, the Mueller matrix roots decomposition is reviewed and a set of Mueller matrix generators are discussed. The parameterization of depolarization into three families, each with three degrees of freedom is explained. Analysis of the matrix roots parameters in terms of degree of polarization maps demonstrates that depolarizers fall into two distinct classes: amplitude depolarization in one class, and phase and diagonal depolarization in another class. It is shown that each depolarization family and degree of freedom can be produced by averaging two non-depolarizing Mueller matrix generators. This is extended to provide further insight on two sample measurements, which are analyzed using the matrix roots decomposition. Chapter 4 discusses additional properties of the Mueller matrix roots generators and parameters, along with a pupil aberration application of the matrix roots decomposition. Appendix C, adapted from a conference proceedings paper, presents an application of the matrix roots depolarization parameters for estimating the orientation of a one-dimensionally textured object. The last two chapters are on the topic of polarization computer generated holography. In chapter 5, an interlaced polarization computer-generated hologram (PCGH) is designed to produce specific irradiance and polarization states in the image plane. The PCGH produces a tangentially polarized annular pattern with correlated speckle, which is achieved by a novel application of a diffuser optimization method. Alternating columns of orthogonal linear polarizations illuminate an interlaced PCGH, producing a ratio of polarization of 88% measured on a fabricated sample. In chapter 6, an etched calcite square-wave retarder is designed, fabricated, and demonstrated as an illuminator for an interlaced polarization computer generated hologram (PCGH). The calcite square-wave retarder enables alternating columns of orthogonal linear polarizations to illuminate the interlaced PCGH. Together, these components produce a speckled, tangentially polarized PCGH diffraction pattern with a measured ratio of polarization of 84% and a degree of linear polarization of 0.81. An experimental alignment tolerance analysis is also reported.