Thesis (Ph.D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 15, 2006) Vita. Includes bibliographical references.

Two optical design scenarios—imaging and illumination—were investigated for their use of Cartesian- and polar-based functions to generate freeform optical surfaces. The imaging scenario investigated a single-element, refracting freeform surface that converts an on-axis object field to an off-axis image point. XY polynomials (Cartesian but not orthogonal) and Zernike polynomials (Polar and orthogonal) were the two different function sets used to manipulate the surfaces to achieve the freeform imaging scenarios. The investigation discovered that the results between both function sets did not differ enough to single out a more effective surface type. However, the results did indicate that the Zernike function set typically required fewer coefficients to converge on an optimal imaging solution. The illumination scenario utilized an architectural lighting situation surrounding the Rothko exhibit for Green on Blue at the University of Arizona Museum of Art. The source location was fixed to the light track in the exhibit space and pointed in many different orientations towards the painting. For each orientation, a point cloud of a freeform optical surface was generated such that the painting surface was illuminated with uniform and low-level light. For each of these generated point clouds, a Legendre (Cartesian and orthogonal) and a Zernike (polar and orthogonal) fitting function was applied, and the convergence results were compared. In general, it was found that, after the 20th included fit term, the Legendre function resulted in a smaller RMS fit error than the Zernike function. However, if the light source was pointed near the center of the painting, the Zernike function converged on a solution with fewer fit terms than Legendre. Amidst the imaging scenario, a definition for the extent to which a surface was freeform, or the "freeformity", was given. This definition proved to be an effective solution when the image size was compared for an F/3.33, F/4, F/5, and F/6.67 system for a range of different image focusing heights: the image size trends for each F-number overlapped, indicating a universal freeform term. In addition, a recursive formula for Cartesian Zernike polynomials was defined, which was used to generate an infinite number of Zernike terms using one single recursive expression.

One of the challenges in tissue engineering is to fabricate scaffolds which can mimic the natural microenvironments of cells. In a cell niche, biophysical and mechanical cues are crucial factors influencing cell functions. Given the complexity of natural extracellular matrix (ECM) engineered ECMs providing controllable biophysical and mechanical cues are appealing both in enhancing the understanding of cell-matrix interaction and in controlling cell fates in vitro. The ultimate goal of our study is to establish a platform as an engineered ECM by fabricating customized solid protein microstructures from solution using two-photon photochemical crosslinking, a novel laser-based freeform fabrication technique. In this study, protein structures varying from submicron lines, 2D micropatterns and microporous matrices, to 3D micropillars were successfully fabricated, demonstrating freeform fabrication capability with two-photon photochemical crosslinking. Two-photon fluorescent imaging and scanning electron microscope (SEM)-based microstructural characterization revealed that power, scan speed, total exposure time and concentrations of protein (bovine serum albumin) and photosensitizer (rose Bengal) in the solution were crucial processing parameters in this fabrication technique. Quantitative imaging analysis showed that porosity of protein matrices was highly dependent on processing parameters including power, scan speed, number of cycles in time series scan and protein concentrations in the solution. An atomic force microscopy (AFM)-based step change nano-compression test was used to measure the reduced elastic modulus of 3D viscoelastic protein micro-pillars fabricated, as a pilot study. Microporous protein matrices and 3D micropillar arrays fabricated with two-photon photochemical crosslinking can be used as engineered ECM for future study in cell-ECM interactions. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 90-100).

Freeform optics provide excellent performance for a wide variety of applications. However, obtaining an accurate freeform surface measurement is highly challenging due to its large aspheric/freeform departure. It has been proven that SCOTS (Software Configurable Optical Test System), an advanced deflectometry system developed at the University of Arizona, can measure the departure of a freeform surface from the desired shape with nanometer accuracy. Here, a new data processing technique was used to measure a freeform surface without any prior knowledge of the shape of the surface. Knowing only the geometry of one point on the test surface, this method can take a blind measurement of a freeform surface and arrive at the true surface through iterative construction.

Le besoin en haute performance en termes de qualité image, résolution et champ de vue accroît la complexité et le budget masse/volume des instruments optiques. Ces contraintes impactent toutes les applications: l’astronomie, la défense, les missions spatiales, la médecine, les objectifs d’appareil photos et caméras, les smartphones, les drones. Afin de résoudre cette problématique dans les instruments d’observation astronomique, je considère deux technologies : les optiques freeform et les détecteurs courbes, qui offrent une nouvelle ère pour le design de systèmes optiques.L’augmentation de la taille des télescopes en orbite basse est nécessaire pour atteindre une observation planétaire à haute résolution spatiale, ce qui implique des systèmes d’imagerie complexes et de grand plans focaux. L’utilisation de systèmes d’imagerie homothétiques aux satellites à défilement Spot et Pleiades mènerait à des dimensions de plans focaux prohibitifs, tout particulièrement pour des missions en infrarouge nécessitant un cryostat. Deux télescopes optiques sont présentés, ils utilisent un module de segmentation composé de miroirs freeform qui permet de réduire considérablement la dimension du plan focal. Les capteurs courbes permettent réduire de manière considérable la complexité des imageurs et des spectromètres en corrigeant directement l'aberration de courbure de champ en plan focal. Je présente des études comparatives sur des systèmes optiques grand champ depuis des champs de vue astronomiques jusqu’à celui du Fishseye, ainsi que les résultats obtenus avec nos deux prototypes d’objectif grand champ utilisant les premiers capteurs courbes CMOS visibles full-frame. / The need of high performance in terms of image quality, high resolution and wide field of view increases the complexity and the volume/mass budget of telescopes and their instruments. Such constraints concern also a wide range of applications: astronomy, defense and surveillance, space missions, biomedical imaging, camera objectives, smartphones, drones. To overcome these issues in astronomical instruments, I consider two technologies: freeform optics and curved sensors, offering a new era for the design of optical systems.Increasing the size of low-orbiting space telescopes is necessary to reach high resolution observation of planets, which implies more complex imaging systems and large focal planes. The use of homothetic imaging systems as Spot and Pleiades pushbroom satellites would lead to prohibitive large linear focal plane dimensions, especially for infrared missions requiring a cryostat. Two optical telescopes are presented, they use an image segmentation made of freeform mirrors which allows to reduce significantly the size of the focal plane. Curved sensors enable to reduce drastically the complexity of imagers and spectrometers by correcting the field curvature aberration directly in the focal plane. I present comparative studies on wide field optical designs from astronomical to Fisheye instruments and the results obtained with our two wide field imaging prototypes using the first visible full-frame CMOS curved sensors.

Slow-servo single-point diamond turning as well as advances in computer controlled small lap polishing enable the fabrication of freeform optics, specifically, optical surfaces for imaging applications that are not rotationally symmetric. Freeform optical elements will have a profound importance in the future of optical technology. Orthogonal polynomials added onto conic sections have been extensively used to describe optical surface shapes. The optical testing industry has chosen to represent the departure of a wavefront under test from a reference sphere in terms of orthogonal φ-polynomials, specifically Zernike polynomials. Various forms of polynomials for describing freeform optical surfaces may be considered, however, both in optical design and in support of fabrication. More recently, radial basis functions were also investigated for optical shape description. In the application of orthogonal φ-polynomials to optical freeform shape description, there are important limitations, such as the number of terms required as well as edge-ringing and ill-conditioning in representing the surface with the accuracy demanded by most stringent optics applications. The first part of this dissertation focuses upon describing freeform optical surfaces with φ-polynomials and shows their limitations when including higher orders together with possible remedies. We show that a possible remedy is to use edge-clusteredfitting grids. Provided different grid types, we furthermore compared the efficacy of using different types of φ-polynomials, namely Zernike and gradient orthogonal Q-polynomials. In the second part of this thesis, a local, efficient and accurate hybrid method is developed in order to greatly reduce the order of polynomial terms required to achieve higher level of accuracy in freeform shape description that were shown to require thousands of terms including many higher order terms under prior art. This comes at the expense of multiple sub-apertures, and as such iv computational methods may leverage parallel processing. This new method combines the assets of both radial basis functions and orthogonal phi-polynomials for freeform shape description and is uniquely applicable across any aperture shape due to its locality and stitching principles. Finally in this thesis, in order to comprehend the possible advantages of parallel computing for optical surface descriptions, the benefits of making an effective use of impressive computational power offered by multi-core platforms for the computation of φ-polynomials are investigated. The φ-polynomials, specifically Zernike and gradient orthogonal Q-polynomials, are implemented with a set of recurrence based parallel algorithms on Graphics Processing Units (GPUs). The results show that more than an order of magnitude speedup is possible in the computation of φ-polynomials over a sequential implementation if the recurrence based parallel algorithms are adopted.

We present an optical surface in closed form that can be used to design lenses for controlling relative illumination on a target surface. The optical surface is constructed by rotation of the pedal curve to the ellipse about its minor axis. Three renditions of the surface are provided, namely as an expansion of a base surface, and as combinations of several base surfaces. Examples of the performance of the surfaces are presented for the case of a point light source. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

This article reports the recent progress of re-search made in the Droplet-Based Manufacturing Laboratory at MIT. The study has been focused on obtaining a fundamental understanding of microdroplet deposition and applying the technology to various practical applications. Specific scientific contributions include the development of an analytical model for droplet splashing/recoiling, an in situ droplet size control methodology, and a study of microstructure design for spray forming. The research per-formed in the lab provides both fundamental knowledge base and practical process developments for a range of manufacturing applications, including electronics packaging, spray forming and freeform fabrication. / Singapore-MIT Alliance (SMA)