Browsing by Subject "Lenses"
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Item Micro/nano fabrication of polymeric materials by DMD-based micro-stereolithography and photothermal imprinting(2006) Lu, Yi; Chen, ShaochenThe revolutionary advancement in semiconductor device manufacturing promoted micro/nano fabrication technologies viable for research and applications in broader fields such as biology and optics. This dissertation is aimed at developing parallel fabrication technologies for polymeric micro/nano structures that can potentially be used in biomedical or optical devices. The objective of the dissertation is three told: a) develop and characterize a digital micro-mirror device (DMD)-based micro-stereolithographic system and explore the fabrication of hydrogel tissue engineering scaffolds, b) use the micro-stereolithographic system to fabricate microlens arrays, c) develop a photothermal imprinting technique to pattern nanostructures on the surface of polymer composites. In the first part of the dissertation, we demonstrated a simple and fast, layer-by-layer micro-stereolithographic system based on DMD dynamic photomask that allows fabrication of complex internal features along the precise spatial distribution of biological factors inside a single scaffold. Photo-crosslinkable poly(ethylene glycol) diacrylate and diamethacrylate were used as the scaffold material. In situ encapsulation of fluorescently-labeled micro-particles and cells was demonstrated. We investigated the photopolymerization process and its effects on the properties of the scaffolds. This technique could provide a powerful tool in studying progenitor cell behavior and differentiation under biomimetic, three-dimensional (3D) culture conditions. In the second part, we developed a novel fabrication technique for microlens arrays using a modified DMD-based micro-stereolithographic system. The DMD can generate high resolution images with quasi-continuous intensity gradient, thanks to its high density mirror elements with a bandwidth of 10 KHz. The projected UV patterns were simply drawn in a computer software. Topographic patterns were created in photocurable resin by spatially controlling the curing depth. Spherical microlens arrays were fabricated and their optical performance was characterized. This technique is capable of fabricating optical elements with any surface topography. In the third part, we discussed the photo-induced radical polymerization. A numerical model was established to correlate the geometry of the resulting gels and system parameters. In the fourth part, we reported a laser-assisted photothermal imprinting method for directly patterning carbon nanofiber reinforced polyethylene nanocomposite. A single laser pulse was used to melt/soften a thin skin layer of polymer nanocomposite. Meanwhile, high resolution patterns were transferred from a quartz mold to the surface of the composite.Item Sub-wavelength electromagnetic phenomena in plasmonic and polaritonic nanostructures: from optical magnetism to super-resolution(2007-12) Urzhumov, Yaroslav A., 1979-; Shvets, G.Effective medium theory of sub-wavelength metallic, semiconducting and dielectric nanostructures that encompasses their electric, magnetic and magnetoelectric response at optical frequencies is introduced. Theory development is motivated by the recent surge of interest in electromagnetic metamaterials: nanostructured composites with unusual or naturally unavailable electromagnetic properties. Unlike numerous other studies, this work focuses on strongly sub-wavelength (unit cell size a λ/n) structures inasmuch as non-subwavelength composites, in general, cannot be described with effective medium parameters. The theory starts from purely electrostatic description of non-magnetic composites and uses plasmon eigenfunctions as the basis. Magnetism and other retardation phenomena are taken into account as perturbations of electrostatic equations. Theoretic description is validated by experimental data on extraordinary optical transmission through subwavelength hole arrays in crystalline silicon carbide films. It is shown that one of the most amazing applications of optical metamaterials, known as the “superlens”, enables deeply sub-wavelength spatial resolution not limited by Abbe’s resolution of a microscope. Theoretical grounds and designs of proof-of-principle verification experiments for near-field sub-wavelength imaging are presented. Theoretical principles and formulas are applied to the problem of engineering an optical negativeindex metamaterial (NIM) that may be used to improve the near-field superlens. NIM engineering begins with simple two-dimensional examples (cylinder arrays, wire pairs) and advances to more complicated metamaterials (strip-film and strip-wire arrays, tetrahedral clusters). Finally, the concept of liquid negative-index metafluids (NIMF) based on plasmonic nanoclusters is introduced and exemplified using tetrahedral cluster colloids. Clusters of plasmonic nanospheres, known as Artificial Plasmonic Molecules (APM), can be easily fabricated in macroscopic amounts and, depending on their symmetry, may exhibit three-dimensionally isotropic electromagnetic response.