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A theoretical and experimental study of the three-ring electrostatic lens is presented. The lens consists of three isolated ring-shaped conductors, equally spaced along a common axis of symmetry. When appropriate potentials are applied to the conductors an electric field is produced near the axis which is capable of focusing a collimated beam of electrons. In the theoretical study the charge density method is used to find a closed-form solution for the field. This method approximates the field by replacing each ring with an infinitely thin hoop of uniform charge. The radial and axial equations of motion are then solved numerically, and the paraxial values of focal length, focal distance and their second order aberrations are found. In the experimental study these focal quantities are determined by a ray tracing method that uses two grids placed in the beam path outside the field of the lens. One grid is placed in front of the lens while the other is placed behind it. The shadow pattern cast by the grids is then analyzed to find the focal properties. This method, which is independent of the type of lens being investigated, is also used on a plano-convex glass lens. Comparison of the experimental and theoretical results shows satisfactory agreement in both cases.

The purpose of this thesis was to investigate age related variations in anterior ocular characteristics and their effect on the response to short-term (one-hour) open eye orthokeratology (OK) lens wear and overnight hydrogel lens wear. Sixty-three volunteer subjects were divided into three groups comprising children (Group I), young adults (Group II) and older adults (Group III). Anterior ocular characteristics that were measured included corneal topography with the Medmont corneal topographer, total, stromal and epithelial thickness with the Holden-Payor optical pachometer, microscopic cell characteristics with the confocal microscope, corneal aesthesiometry, corneal modulus of elasticity, and tear film, palpebral and eyelid characteristics. The older cornea was found to be more spherical in shape (asphericity Q = -0.24 ?? 0.07 in group III compared to -0.34 ?? 0.09 and -0.32 ?? 0.17 in groups I and II respectively) and showed a tendency from with-the-rule to against-the-rule astigmatism. Older subjects also had a decreased endothelial cell density (2596 ?? 111 cells/mm2 in group III compared to 2793 ?? 138 cells/mm2 in group II) and reduced eyelid tension compared to the younger groups. Children were found to have lower blink rates than adults. It was concluded that these changes might have a significant impact on contact lens wear. The responses to two contact lens based techniques, orthokeratology (OK) and hydrogel overnight wear (ON), were studied. Sixty subjects (20 per group) wore reverse-geometry lenses (BE, Ultravison Aust Pty Ltd) of Boston XO material in one eye under open eye conditions for one hour in one eye only. Changes in unaided visual acuity, corneal curvature, corneal thickness and confocal microscopic variables were measured after OK lens wear. All subject groups showed statistically significant improvements (p &lt 0.05) in unaided visual acuity, a trend for more positive (less prolate) corneal asphericity, increase in apical corneal radius and decrease in central total corneal thickness, after OK lens wear. When the groups were stratified, statistical significance was obtained between the older group and the other two younger groups for change in apical corneal radius (0.23 ?? 0.01 mm in group I, 0.15 ?? 0.01 mm for group II, 0.06 ?? 0.33 for group III). The change in asphericity also showed significant differences between the older age group (0.10 ?? 0.08 mm) and the young adult group (0.21 ?? 0.13). Central corneal thinning obtained after one hour of OK lens wear revealed significant differences between the older adult group (-1.9 ?? 3.2 ??m) and the other two groups (-5.0 ?? 5.9 ??m in group I, -5.0 ?? 2.0 ??m for group II). Sixty subjects wore hydrogel lenses (One-Day Acuvue, Johnson and Johnson Visioncare Pty Ltd) made of etafilcon A in one eye only overnight during sleep at their home. Changes in unaided visual acuity, corneal curvature, corneal thickness, confocal microscopic variables and slitlamp variables were measured after ON lens wear. All subjects showed significant thickening (p &lt 0.05) of the cornea with ON wear, more in the lens-wearing eye. This study reported that the edema response induced by Acuvue contact lenses is stromal in origin. The edema response of the older group (33.9 ?? 11.5 ??m) was lower than the other two groups as demonstrated by the difference in the change in central stromal thickness (49.3 ?? 20.3 ??m for group I and 51.0 ?? 20.0 ??m for group II). However, a statistically significant difference in the change in thickness was not reached either for the central total corneal thickness or for other topographic locations. Corneal and visual changes found in this study confirm previous reports of the effects of short term OK and hydrogel ON lens wear. Older lens wearers showed a reduced or delayed response to short-term lens wear. Studies investigating the effects of age with long lens-wearing durations are warranted to quantify these effects further.

The use of optics in the fields of nano-technology, telecommunication and medicine has been growing exponentially in recent years. Application of liquid crystals within optics has been a growing trend from flat screen displays to variable focus lenses in a digital versatile discs. One area of the recent developments within optics has been the development of two-photon fluorescence microscopy and high-density three-dimensional optical data storage. In such applications, where a light beam has to be focused deep within the volume of bulk media, aberrations are introduced. The most dominant aberration is spherical aberration which results from the mismatch in refractive indices of the immersion and recording media. The aim of this thesis is to design a liquid crystal lens for dynamic tube length compensation of the spherical aberration. Liquid crystal phase plates are used in everyday liquid crystal displays (LCDs) such as mobile phones and calculators. The technologies required to manufacture a liquid crystal phase plate are well understood. However, an application like three-dimensional data storage requires different properties in the liquid crystal phase plate, which are investigated in this thesis. To fabricate our liquid crystal phase plate we used ZLI-5049-000 from MERCK as the liquid crystal medium, with poly-vinyl alcohol (PVA) and Indium Tin Oxide (ITO) providing the insulating and conducting layers, respectively. It has been demonstrated that vacuum vapour deposition can be used to coat a glass substrate with ITO. However, in order for the ITO coating to be conductive a method is developed where the substrate is heated to 300oC before, during and after the coating. Similarly, a method has been developed for producing a uniform 10 μm coating of PVA on top of the ITO. In order to produce a liquid crystal lens with the properties required to compensate for spherical aberration an investigation into the properties of the liquid crystals is first conducted. A liquid crystal phase plate described in chapter 3 is characterised to determine the effect of the rubbing direction of the insulating layer and the effective refractive index change with applied voltage. It has been demonstrated that an effective change in refractive index of 0.11 can be achieved with 30 volts applied across the ITO electrodes. Based on the characterisation of the liquid crystal phase plate four different liquid crystal lens designs have been proposed and tested. The lens designs are based upon convergent and divergent lenses with different refractive index lens substrates. It is determined that a liquid crystal lens with a divergent lens substrate with a refractive index of 1.785 can be used to effectively compensate for spherical aberration. This has been confirmed experimentally by using the liquid crystal lens in a two-photon confocal microscope and measuring a increase in detected intensity at a depth below the surface of a sample. The research conducted in this thesis shows the ability to dynamically compensate for spherical aberration introduced by a mismatch in the refractive indices between the immersion and sample mediums. It has also been demonstrated that new methods for fabricating the conductive and insulating layers are suitable for producing a liquid crystal lens. A liquid crystal lens based on the research in this thesis could be used in three-dimensional data storage or microscopy applications.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy & Astrophysics. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, August 2001. / Includes bibliographical references. Also available on the Internet.

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