Thesis advisor: Willie J. Padilla / Progress in the field of metamaterials has started coming to a point where the field may finally begin to emerge as a viable solution to many electromagnetic challenges facing the community. No where is that more true then at terahertz frequencies where there lies an immense opportunity for growth. The development of mature technologies within this region of the electromagnetic spectrum would provide a valuable resource to become available for a multitude of applications. In order to achieve this, the necessary first steps of identifying viable materials and paths to integrate these with metamaterials will need to be completed. In this dissertation, we examine several different paths to achieve dynamic metamaterial electromagnetic response at terahertz frequencies, and demonstrate several paths to package these devices into imaging systems. In Chapter 1, we introduce the basic theory and design principles of metamaterials. We also describe the experimental techniques involved in the study of terahertz metamaterials. Chapter 2 presents a computational and experimental study investigating the integration of high electron mobility transistors with metamaterials allowing for high speed modulation of incident terahertz radiation. In Chapters 3 and 4, we investigate several different paths to create tunable terahertz metamaterial absorbers. Chapter 3 presents an investigation where we encapsulate a metametarial absorber unit cell with liquid crystals. We study both computationally and experimentally the tuning mechanism of the absorber as the liquid crystal refractive index is controlled as a function of the applied electric field strength and modulation frequency. In Chapter 4, we form a doped semiconducting metamaterial spatial light modulator with multi-color super-pixels composed of arrays of electronically controlled terahertz metamaterial absorbers. We computationally and experimentally study the independent tunability of each pixel in the spatial array and demonstrate high speed modulation. Chapter 5 introduces a multiplex imaging approach by using a terahertz spatial light modulator to enable terahertz imaging with a single pixel detector. We demonstrate the capability for high speed image acquisition, currently only limited by the commerical software used to reconfigure the spatial masks. We also configure the system to capture high fidelity images of varying complexity. In Chapter 6, we show how a metamaterial absorber can be implemented into a detector focal plane array for high sensitivity, low mutual coupling, and broad angle performance. Finally, we summarize in Chapter 7 the achievments of the research presented and highlight the direction of future work. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The purpose of this thesis is to develop a low-cost, high power laser diode/fiber illumination system and to design the driver electronics of the spatial light modulator (SLM) for holographic, three dimensional (3D) imaging. A miniaturized laser diode/fiber/polarizing illumination system capable of 15mW of output at a wavelength of 690nm is designed, fabricated, and tested. The size limitations of various commercially available SLM drivers are described and the design to overcome them is suggested. The design describes in detail the timing considerations of the hardware interface and the psuedocode of the software interface between the host computer and the SLM. Experiments carried out to study the spatial uniformity of the SLM and the distortion due to the beam splitter on the structured output from the LIM are explained. / Master of Science

A miniaturized spatial light modulator (SLM)-based structured-light illumination module with optical fiber input is designed to generate a coded 256 x 256 spots pattern for 3-D areal mapping applications. The projector uses the light from a He-Ne laser coupled to a polarization-maintaining (PM) fiber to illuminate a specially made hologram so that four virtual point sources are regenerated. The interference pattern of the four sources are filtered and modulated by an SLM. The output intensity can thus be encoded to form any arbitrary pattern through the electronic input applied to the SLM with a high speed. In this thesis, a complete optical diffraction analysis of the system is presented to provide guidelines for the optimal design of the system parameters. Through the theoretical analysis for square beam array generation, the important parameters for fabricating a hologram are given. The final system optical design and arrangement based on optical analysis are described. The detailed opto-mechanical construction of the LIM and the associated alignment, the computer simulation and the preliminary test results of the developed LIM are also provided. / Master of Science

Laser beams with precisely controlled intensity profiles are essential for many areas. We developed a beam shaping system based on the digital micromirror device (DMD) for ultra-cold atom experiments and other potential applications. The binary DMD pattern was first designed by the error diffusion algorithm based on an accurate measurement of the quasi-Gaussian incident beam from a real-world laser. The DMD pattern was projected to the image plane by a bandwidth-limited 4f telescope that converted this pattern to the grayscale image. The system bandwidth determined the theoretical limit of image precision by the digitization error. In addition, it controlled the spatial shape of the point spread function (PSF) that reflected the tradeoff between image precision and spatial resolution. PSF was used as a non-orthogonal basis set for iterative pattern refinement to seek the best possible system performance. This feedback process, along with stable performance of DMD, the blue-noise spectrum of the error diffusion algorithm, and low-pass filtering, guaranteed high-precision beam shaping performance. This system was used to produce various beam profiles for different spatial frequency spectra. First, we demonstrated high-precision slowly-varying intensity beam profiles with an unprecedented high intensity accuracy. For flattop and linearly-tilted flattop beams, we achieved 0.20-0.34% root-mean-square (RMS) error over the entire measurement region. Second, two-dimensional sinusoidal-flattop beams were used to evaluate image precision versus system bandwidth. System evaluation confirmed that this system was capable of producing any spatial pattern with <3% RMS error for the most system bandwidth. This experiment extended the beam shaping to any system bandwidth and provided a reference to estimate the output image quality based on its spatial spectrum. Later experiment using a Lena-flattop beam profile demonstrated the arbitrary beam profile generation. We implemented this system for applications on the homogenous optical lattice and dynamic optical trap generation. The DMD pattern was optimized by the iterative refinement process at the image feedback arm, and projected through a two-stage imaging system to form the desired beam profile at the working plane. Experiments demonstrated a high-precision beam shaping as well as a fast and dynamic control of the generated beam profile. / text

Thesis (PhD)--Stellenbosch University, 2015.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Ultra-short laser pulses are useful in materials processing like melting and cutting metals, and medical applications such as surgery and many other fields. In this study, we characterize and control the temporal shape of the ultra-short pulses generated from a Ti:Sapphire femtosecond laser. It operates in the near infra-red spectral region, with a centre wavelength of 800 nm. The 4f pulse shaper is the main setup used to modulate spectral shape and characterize the laser pulse. The shaper consists of two diffraction gratings, two cylindrical lenses and a computer controlled liquid crystal spatial light modulator (LC-SLM). Gratings, lenses and LC-SLM are arranged in a 4f geometry, f being the focal length of the lenses. This setup is first analysed analytically and numerically using Fourier transform and the results obtained are then compared to those obtained from the experiment. The characterization of ultra-short pulses was done using three different autocorrelation techniques such as the intensity autocorrelation, the interferometric autocorrelation, and the pulse shaping autocorrelation which can act as interferometric autocorrelation when a nonlinear crystal ß-barium borate (BBO) is placed exactly at the position of the experiment. These characterization techniques are based on the interaction between the laser pulse and a replica of it with a nonlinear crystal. The setups were implemented and measurements using the last two techniques were successfully conducted, with the pulse duration result in the range from 80-86 fs. / AFRIKAANSE OPSOMMING: Ultrakort laserpulse het baie nut in verskeie velde waaronder materiaalprosessering (soos die smelt en sny van metale) en mediese toepassings (soos chirurgie) maar net twee voorbeelde is. In hierdie studie karakteriseer en beheer ons die vorm van n ultrakort laserpuls, afkomstig vanaf n Ti:Saffier femtosekonde laser, in tyd. Die laser straal in die nabyinfrarooi spektrale gebied uit met n sentrale golflengte van 800 nm. Ons gebruik n sogenaamde 4f-pulsvormer om die spektrum van die laserpuls te moduleer en die laserpuls te karakteriseer. Die vormer bestaan uit twee diffraksieroosters, twee silindriese lense en n rekenaarbeheerde vloeibare kristal ruimtelike-lig-modulator (LC-SLM). Die diffraksieroosters, lense en LC-SLM is in n 4f-geometrie gerangskik, met f die brandpunt van die lense. Die opstelling is eers analities en numeries beskou deur van Fourier-transformasies gebruik te maak waarna die resultate wat verkry is met die van n eksperiment vergelyk is. Die karakterisering van ultrakort laserpulse was met drie verskillende outokorrelasie tegnieke gedoen, naamlik n intensiteits-outokorrelasie, n interferometriese-outokorrelasie en n pulsvormer-outokorrelasie. Die pulsvormer kan as n interferometriese-outokorrelator optree indien n nie-lineêre kristal ß-bariumboraat (BBO) by die uitset van die pulsvormer geplaas word. Hierdie karakteriseringstegnieke is gebaseer op die interaksie tussen die oorspronklike laserpuls en n kopie van die laserpuls in n nie-lineêre kristal. Die nodige opstellings virdie metings is gemaak en die metings was suksesvol uitgevoer. Die pulslengte wat gemeet is, is in die orde van 80-86 fs.

Ce manuscrit de thèse traite de l’étude de verres ophtalmiques microstructurés et plus particulièrement pixellisés, ces derniers pouvant présenter un intérêt particulier en optique active pour la correction de la presbytie. Une étude théorique est proposée, permettant d’analyser les performances optiques d’une lentille pixellisée en termes de transport d’image et d’identifier les paramètres qui ont un impact direct sur ces performances. Après validation expérimentale des résultats obtenus, nous constatons puis expliquons l’effet sur l’observation d’une scène de l’excentrement de l’œil par rapport à la fonction de phase du verre. Nous étudions l’effet du repliement de phase inhérent aux limites des technologies de fabrication, qui vient ajouter un chromatisme axial aux défauts visuels engendrés par la pixellisation. Nous nous intéressons ensuite aux applications possibles de la pixellisation en optique passive. Nous prouvons que pour une application visée, des lentilles binaires non pixellisées, dont nous optimisons la qualité optique, conduisent à de meilleurs résultats que les lentilles pixellisées. L’impact sur l’acuité visuelle des phénomènes diffractifs parasites induits par la pixellisation est évalué au moyen d’un banc de mesure utilisant la simulation de certaines images telles qu’elles seraient vues au travers de verres ophtalmiques pixellisés. Enfin, nous menons une étude de l’aspect esthétique d’un verre pixellisé vu par un observateur externe, à partir de modèles de calcul hybrides mêlant optique géométrique et optique de Fourier. / This thesis investigates microstructured and more particularly pixelated ophthalmic glasses, the latter raising some hope for the active correction of presbyopia. A theoretical study is developed for the analysis of the optical performances of a pixelated lens in terms of image transport and leads to the identification of the parameters which have an impact on these performances. After experimental validation of the results obtained, we note and then explain the effect on the observation of a scene of eye displacement with respect to the optical function of the eyeglass. We study the effect of phase wrapping, which is inherent in the limits of the technologies implied in the manufacturing process and adds an axial chromatism effect to the visual defects generated by pixelation. We are also interested in the potential applications of pixelation in the field of passive optics. We prove that for a given application, non pixelated binary lenses, the optical quality of which we optimize, lead to better results than pixelated lenses. The impact on visual acuity of the parasitic diffractive phenomena induced by pixelation is evaluated with an optical bench using the simulation of test images seen through pixelated lenses. Finally, we study the aesthetic aspect of a pixelated component as seen by an external observer, using hybrid calculation models based on both geometrical and Fourier optics.

Three-dimensional (3D) displays project 3D images that give 3D perceptions and mimic real-world objects. Among the rich varieties of 3D displays, multiview displays take advantage of light’s various degrees of freedom and provide some of the 3D perceptions by projecting 2D subsampling of a 3D object. More 2D subsampling is required to project images with smoother parallax and more realistic sensation. As an additional degree of freedom with theoretically unlimited state space, orbital angular momentum (OAM) modes may be an alternative to the conventional multiview approaches and potentially project more images. This research involves exploring the possibility of encoding/decoding off-axis points in 2D images with OAM modes, development of the optical system, and design and development of a multiview colour display architecture. The first part of the research is exploring encoding/decoding off-axis points with OAM modes. Conventionally OAM modes are used to encode/decode the on-axis information only. Analysis of on-axis OAM beams referenced to off-axis points suggests representation of off-axis displacements as a set of expanded OAM components. At current stage off-axis points within an effective coding area are possible to be encoded/decoded with chosen OAM modes for multiplexing. Experimentally a 2D image is encoded/decoded with an OAM modes. When the encoding/decoding OAM modes match, the image is reconstructed. On the other hand, a dark region with zero intensity is shown. The dark region suggests the effective coding area for multiplexing. The final part of the research develops a multiview colour display. Based on understandings of off-axis representation of a set of different OAM components and experimental test of the optical system, three 1 mm monochromatic images are encoded, multiplexed and projected. Having studied wavelength effects on OAM coding, the initial architecture is updated to a scalable colour display consisting of four wavelengths.

Las aberraciones ópticas determinan la formación de imágenes en el ojo, tanto en el proceso de la visión como en las observaciones oftalmoscópicas del fondo de ojo. La corrección total de estas aberraciones permitiría una resolución limitada sólo por la difracción en las pupilas utilizadas. Las aberraciones del ojo difieren de un sujeto a otro y no responden a modelos sencillos. En este trabajo se propone el uso de técnicas de Óptica Adaptativa para el desarrollo de un sistema experimental para la medida y corrección de las aberraciones estáticas del ojo. Estas técnicas pueden ser igualmente útiles para obtener imágenes de alta resolución de la retina, utilizarse en el diseño de lentes oftálmicas, etc. Para la medida de la función aberración de onda, se han utilizado dos métodos no invasivos aplicables al ojo humano: La Recuperación de Fase a partir de dos imágenes de Doble Paso, y el Sensor de Hartmann-Shack. Para la corrección de la aberración se ha utilizado un Modulador Espacial de Cristal Líquido.Se han desarrollado los procedimientos de control y de calibrado de estos métodos, y se estudia la viabilidad de aplicación para el ojo. Finalmente, se han realizado medidas de la aberración, mediante ambos métodos, y su posterior corrección mediante el modulador espacial de cristal líquido, en un ojo artificial y en sujetos reales. / The image formation properties of the eye are determined by the aberrations of the optics. The complete correction of the aberrations would allow diffraction-limited resolution. The aberrations of the eye are not easily modeled and are different for each subject.This thesis proposes the use of adaptive optics techniques to measure and correct the static aberrations of the eye. The principles and methods developed are useful in specific applications, i.e., high-resolution retinal imaging, ophthalmic lens design, etc.Two non-invasive methods have been used to measure the wave aberration function: Phase Retrieval Techniques from two double-pass retinal images; and the Hartmann-Shack sensor. A Liquid Crystal Spatial Light Modulator was used to adaptively correct the wave front aberration of the eye.This thesis also includes guidelines to calibrate and control the proposed techniques.Finally, experimental explorations of these methods are reported. Several results are presented, including the measure and the subsequent compensation of the wave aberration for artificial and human eyes.

The problem of zero order diffraction (ZOD) in the computer generated hologram (CGH) is a commonly reported issue in employing computer generated hologram (CGH) systems. Failing to remove the zero order diffraction in either far-field or near-field region limits the display region or even worse, can destroy the reconstructed image. Therefore, the elimination of the ZOD is higly desired. The proposed new techniques to suppress the ZOD are the backbone of this thesis. We investigated ZOD sources in two different CGH systems and suggested different methods to remove the ZOD in each system. Two types of spatial light modulator (SLM) were employed for different type of CGHs, including a phase-only SLM and a binary amplitude-only SLM. All the proposed methods were examined with either simulation and experimental tests. For amplitude-only experiments, the ZOD suppression reached a factor of 3. Image quality and diffraction efficiency were also investigated for the proposed methods. / text