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Title: Manufacture of micro-optical elements for imaging and light-guidance
Author: Langridge, Mark T.
ISNI:       0000 0004 5347 8067
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2015
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In this thesis we discuss the manufacture and characterisation of micro-optical elements, for guiding light into sub-wavelength beams & spots, and for use in super-resolution imaging. A physical limit exists in microscopy where it is impossible to view object smaller than half the illuminating wavelength, via conventional means. In white light microscopy this creates an resolution limit of 321nm (at a wavelength of 500nm, in air). This places a limit on the smallest objects a researcher can study using optical microscopy. We present a method for fabricating plano-convex lenses which, when placed in near proximity to the samples, boost magnification of conventional microscopes by up-to 2.5x and resolve features below 200nm, with white light illumination. We also demonstrate a curved axicon Bessel-beam former, that produces long (17 micrometer) non-diffracting beams of light, that can be sub-wavelength in width, down to 2/3rds the wavelength. In this thesis we contribute the following to current knowledge: We describe a focused ion-beam milling technique to form bespoke geometry of parabolic & spherical curvature, including reflective dishes, of diameter 1-10 microns, with a surface roughness of 4.0-4.1nm. As part of this work, we calculate the efficiency of a new technique for removing ion-beam induced damage, using wet-chemical etching. Here we show that increasing the ion-dose above 3000 µC/cm^2 allows a higher percentage of the implantation and amorphisation damage to be removed, and leaves less than 0.5% of the gallium remaining in the surface. We use the ion-milled dishes to form lens moulds; we double-replicate the brittle silicon mould, to create a hard wearing rubber mould. As multiple rubber moulds can be created per silicon mould the process becomes industrially scalable. A thin-film of polymer lenses is then formed from the mould. We characterise these lenses, demonstrating 1.2-2.5x magnification and resolution of 200nm. We demonstrate their use by imaging two biological samples, one fixed & stained, and one unlabelled in water. Additionally, using computer simulations alongside the focused ion-beam manufacturing technique, we demonstrate a curved axicon lens structure, that forms long, non-diffracting beams of intense light. We model and experimentally analyse how the lens profile and high-to-low refractive index change forms the beam, and show that increasing the refractive index change decreases the beam width but at a loss of light transmission.
Supervisor: Stolojan, Vlad; Cox, David C. Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available