Thesis (M.S.)--Rochester Institute of Technology, 1993. / Typescript. Includes bibliographical references (leaves 131-136).

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, December 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2005. / Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, December 1997. / Includes bibliographical references. Also available on the Internet.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 58-60). Also available in electronic version.

Early stage detection of cancerous tissue is critical to increasing the 5-year survival rate for patients. The development of devices capable of accessing and visualizing these tissue sites plays an important role in this process. Many cancer types have existing screening methods however many have proven ineffective in large clinical trials. Since early stages of cancer development often has subtle changes from normal tissue, traditional non-invasive imaging techniques such as ultrasound or magnetic resonance imaging are not able to detect them. The following work evaluates the feasibility of miniaturization of Volume Holographic Imaging (VHI) systems into laparoscopic endoscopes for tissue and cancer screening. The work is divided into two main sections discussing the design and evaluation of each imaging system. The first system is a Reflectance VHI Endoscope designed for simultaneous imaging of two imaging depths within a tissue sample. The system is evaluated for resolution and contrast through imaging of resolution bar targets and soft tissue samples. The second system is a Wavelength Coded VHI Endoscope which combines the Reflectance VHI Endoscope imaging properties with axial chromatic dispersion effects of Gradient Index (GRIN) optics to improve the volume holographic element performance and reduce excess background light. Both Reflectance and Wavelength Coded VHI systems utilize a sub-4 mm diameter rigid relay probe which has been approved for in-vivo applications. The sub-4.4 µm/lp resolution produced by both VHI Endoscope systems and tissue depth separations of 50 µm and 100 µm for the Reflectance and Wavelength Coded designs, respectively, make VHI systems a candidate for clinical evaluation of early stage cancer development.

A computer-controlled ellipsometer was used to obtain data on the birefringence changes induced in lithium niobate crystals by irradiation with an argon-ion laser. The instrument was set to take readings on a rectangular grid of points before and after irradiation. Irradiation was performed with circular and with narrow rectangular light beams. Results are compared with the prediction of the model of Chen in which he postulated the presence of an internal field Eo in the direction of the c-axis of the crystal. According to his theory, electrons, photoexcited from traps by the laser light, drift under the influence of Eo along the c-axis before being retrapped. The resulting space-charge field set between positive ionised centres and trapped electrons gives rise to the observed birefringence changes via the linear electro-optic effect of the crystal. Approximate mathematical models based on Chen's theory are used to solve the problem with narrow rectangular light beams. Results are compared with experiments. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Time-average and stroboscopic real-time holography have become established as the prominent tools of holographic vibration analysis. Both are able to provide a quantitative determination of the amplitudes of standing waves of a vibrating flat surface, but have to date been limited to qualitative examination of curved surfaces. The purpose of this thesis has been to investigate the problems of extending the holographic technique to the analysis of surfaces of single curvature. The presence of several component motions in curved surface vibration prompted an examination of the fringe behaviour of the individual components of motion. This was performed by studying pure rigid body step displacements using double exposure holography. The experimental work of previous investigators was duplicated and the results tabulated according to the sensitivities of the fringe period density to a change in displacement magnitude. This was then related to the rotations and translations occurring in the motion of a vibrating surface. A fully clamped curved panel was studied using the time-average method with the assumption that all points on the surface were displaced normal to it. Good agreement was obtained between the amplitudes calculated from the fringes and the measured amplitudes, by accounting for the variation in displacement direction across the surface. A fixed-free cylinder was examined simultaneously from two overlapping views using both the time-average and stroboscopic real-time methods. Comparison of the calculated and measured amplitudes of the time-average indicated that the interference fringes were not localized upon or very near the cylinder's surface. The real-time results had reinforced these findings. However, the inherent presence of residual fringes in this method caused difficulties in obtaining an accurate quantitative evaluation of the vibration amplitudes. The real-time fringes were analyzed with attention paid to the effects of the initial residual fringes upon the resultant fringes. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Exposure of some insulating crystals such as lithium niobate to light of appropriate wavelength induces small changes in the refractive index. This effect has been named the photorefractive effect. It allows phase holograms to be stored in these crystals. The work to be described was undertaken in order to obtain a better understanding of the hologram storage process which is believed to involve the spatial redistribution of photoexcited electrons among traps. This causes a space charge field to develop which modulates the refractive index via the linear electro-optic effect. A new reliable criterion for deciding whether the Raman-Nath or the Bragg regime of diffraction will be observed with a given hologram was proposed. It is shown that the distinction between "thin" and "thick" holograms is invalid as a criterion for which regime operates. The new bulk photovoltaic effect proposed by Glass et al. is an important mechanism in the photorefractive effect in ferroelectric crystals. It is shown that as formulated by Glass et al. it is formally equivalent to a fictional "virtual field" acting on the photo-liberated electrons provided that their migration length is short compared to the grating spacing. Hologram writing by the photorefractive effect was modelled in progressive stages of complexity. All the models were based on the assumption that the transport length of the free electrons is short compared to the grating spacing. This appeared to be a generally accepted assumption. The first treatment allowed for the feedback effect of the space charge field and for the dark conductivity. It was for uniform illumination and constant applied voltage. The effects of the modulation ratio and the applied field were investigated. This treatment was then modified to allow for the effect of the absorption constant in reducing the intensity of the light as it propagates through the crystal. It was shown that the hologram becomes nonuniform through the crystal thickness as a result of this effect. Hologram writing with one-dimensional Gaussian beams was modelled allowing for the feedback effect of the space charge field. A large scale space charge field associated with the envelope of the light pattern was shown to affect the writing process. It was found that an increase in the fractional illumination of the crystal improves the writing process. The dark conductivity is shown to have an important effect on the process. The final model was again for uniform illumination and allowed not only for the feedback effect of the photoinduced field and the effect of the dark conductivity and absorption but also for the interaction between the hologram being written and the light pattern which is writing it. This causes energy transfer between the two writing beams, thus modifying the light pattern. Optical erasure of holograms with the light incident either on and off the Bragg angle was modelled. The treatment allows for the feedback effect of the space charge fields and for the effect of the absorption in reducing the light intensity. The model allowed for the interaction between the diffracted and the reading beams for the case of incidence at the Bragg angle. The resulting interference pattern writes a new hologram which may add to or subtract from the hologram to be erased. An experimental method is described in which a normally incident ancillary light beam of different wavelength than that used to write the hologram allows the diffraction efficiency to be determined without errors due to multiple internal reflections. A limited experimental investigation was made of hologram storage in LiNbO₃. Photocurrent and optical measurement were carried out on the same crystal. Almost 100% relative diffraction efficiency was observed. The value of the virtual field obtained from holographic measurement was found to agree within 10% with the value obtained from photocurrent measurements. During hologram writing, energy transfer of up to 70% between the two writing beams was observed. However, since the "virtual" field in these experiments was much larger than the diffusion equivalent field, the model predicted only about 5% energy transfer. It is, therefore, suggested that the transport length of the photoexcited electrons in the crystal used, was not short compared to the grating spacing. It is also shown that light induced scattering can cause serious error in measuring the diffraction efficiency expecially during optical erasure. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Metasurfaces are a novel class of optical devices, made up of an array of subwavelength scatterers that can allow unprecedented control of an optical wavefront. These devices can be fabricated using conventional nano and microfabrication processes en masse and have thin and lightweight form factor making them ideal for use in compact and miniaturized optical systems. In this thesis, I will first introduce the field of metasurfaces with a historical overview of the research and development in this field. Following the introductory section, I will demonstrate a design for broadband infra-red absorber based on the metasurface platform, demonstrating the ability of metasurface to control broad spectrum of light. Subsequently, optical wavefront engineering capability of metasurfaces is displayed by demonstration of multifunctional metasurface devices, including examples of multiwavelength metasurface lenses and holograms. An example of polarization multiplexed metasurface will also be discussed. As an extension of multiwavelength metasurface lens, a framework for correcting chromatic dispersion inherent in metasurface is presented. I will then demonstrate a strategy to design metalenses with broadband achromatic aberration correction for imaging applications and discuss fundamentals limitations on the extent of chromatic correction that can be achieved. This will lead to a section on multi-element metasurface design for correcting monochromatic aberration in addition to chromatic aberration for compact imaging systems. Finally, I will conclude the thesis with an outlook that points to application areas where metasurfaces, with their thin and light form factor are ideal alternative to replace many conventional optical devices.