<p> <b>Overview:</b> Optical concepts as they relate to the ophthalmologic correction of vision in corneal laser vision correction and intraocular lens design was examined. </p><p> <b>Purpose:</b> The interaction between the excimer laser and residual corneal tissue in laser vision correction produces unwanted side effects. Understanding the origin of these artifacts can lead to better procedures. Furthermore, accommodating intraocular lenses offer a potential for eliminating presbyopia. Understanding the properties of a new accommodating intraocular lens incorporating a deformable interface may lead to advances in cataract surgery. </p><p> <b>Introduction:</b> Corneal surface irregularities following laser refractive procedures are commonly seen. They regularly result in a patient&rsquo;s decreased best corrected visual acuity and decreased contrast sensitivity. These changes are only seen in biologic tissue and the etiology has been elusive. A thermal response has been theorized and was investigated in this research. In addition, intraocular lenses using a mechanically deforming interface to change their power in order to duplicate natural accommodation have been developed. The deforming interface(s) induce optical aberrations due to irregular deformations. Design efforts have centered on minimizing these deformations. Both of the ophthalmic applications have been analyzed using finite element analysis (FEA) to understand their inherent optical properties. </p><p> <b>Methods:</b> FEA modeling of thermal theory has been applied to verify that excimer laser induced collagen contraction creates corneal surface irregularities and central islands. A mathematical model which indicates the viability of the theory was developed. The modeling results were compared to post ablation changes in eyes utilizing an excimer (ArF 193 nm), as well as non-ablative thermal heating in eyes with a CO₂ laser. </p><p> Addition modeling was performed on an Intraocular lens prototype measuring of actuation force, lens power, interface contour, optical transfer function, and visual Strehl ratio. Prototype verified mathematical models were utilized to optimize optical and mechanical design parameters to maximize the image quality and minimize the required force. </p><p> Results: The predictive model shows significant irregular central buckling formation and irregular folding. The amount of collagen contraction necessary to cause significant surface changes is very small (0.3%). Uniform scanning excimer laser ablation to corneal stroma produces a significant central steepening and peripheral flattening in the central 3mm diameter. Isolated thermal load from uniform CO₂ laser irradiation without ablation also produces central corneal steepening and paracentral flattening in the central 3mm diameter. </p><p> The iterative mathematical modeling based upon the intraocular lens prototype yielded maximized optical and mechanical performance through varied input mechanical and optical parameters to produce a maximized visual Strehl ratio and a minimized force requirement. </p><p> <b>Conclusions:</b> The thermal load created by laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface which correlates to the temperature rise and is not seen inorganic, isotropic material. The highly similar surface changes seen with both lasers are likely indicative of temperature induced transverse collagen fibril contraction and stress re-distribution. Refractive procedures which produce significant thermal load should be cognizant of these morphological changes. </p><p> The optimized intraocular lens operates within the physiologic constraints of the human eye including the force available for full accommodative amplitude using the eye&rsquo;s natural focusing feedback, while maintaining image quality in the space available. Optimized optical and mechanical performance parameters were delineated as those which minimize both asphericity and actuation pressure. The methodology combines a multidisciplinary basic science approach from biomechanics, optical science, and ophthalmology to optimize an intraocular lens design suitable for preliminary trials.</p>

Evaluation of the optical performances of bimetallic mirrors with various substrate shapes was conducted using the finite element analysis program, SDRC-IDEAS. In these analyses, two different plating materials, nickel and aluminum were considered for an aluminum and a beryllium mirror substrate. Thermal environments used in this study are: a unit thermal soak (temperature difference), an axial temperature distribution, and radial temperature distributions on the mirror substrate. The goal of this study is to optimize the optical surface quality for various plating thicknessess. Surface errors, individual aberration terms, such as piston, tilts, focus and other aberrations were obtained by the program PCFRINGE. It was found that the optical performances of bimetallic mirrors depend on the plating material, plating thickness, and the mirror substrate materials. The optimum plating thickness combinations were determined based on plating material and mirror substrate with variation of temperature distributions. The results were compared with the optical surface errors and the corrected surface errors. The results indicate that there does not exist a definite common rule for the optimum, but a detailed analysis such as presented herein is generally needed to design bimetallic mirrors in a thermal environment.

The Remote Sensing Group of the Optical Sciences Center at the University of Arizona performs absolute radiometric calibration of Earth-viewing sensors using vicarious methods. The reflectance and irradiance-based methods require the nadir-view reflectance of a calibration site at sensor overpass. Errors in these reflectance data contribute directly to errors in the retrieved at sensor radiance, and therefore errors in the calibration. This research addresses two areas of improvement for the reflectance retrieval. The discreet laboratory data of the reference panel is spectrally interpolated using the measured hemispherical reflectance rather than a polynomial fit. This interpolation better fits an absorption feature of the reference material near 2200 nm. The desired reflectance is due to the directly-transmitted solar irradiance, but field measurements also include irradiance due to diffuse light. Non-lambertian properties of the reference and surface cause the ratio of the reflected total radiances to differ from the ratio of the reflected solar radiances. This difference can be corrected using additional field measurements, shaded surface/shaded-reference, output from a radiative transfer code, RTC-only, or a combination of both, shaded-reference. For the shaded-reference and RTC-only methods the shape of the bi-directional reflectance factor of the surface must be known to better than 10% to maintain a 2% accuracy for the retrievals, while the shaded-surface/shaded-reference method does not use the surface BRF. All three methods were applied to measurements of calibrated reflectance tarpaulins, and to measurements made at White Sands Missile Range. These data demonstrate that the shaded-surface/shaded-reference and RTC-only methods improve the surface reflectance retrieval, while the shaded-reference method is too sensitive to variations between the actual and modeled diffuse sky irradiance to be useful. This research represents significant improvements in the calculation of surface reflectance for vicarious calibration. The hemispherical reflectance interpolation will reduce uncertainties in the short wave infrared by 1%, and the diffuse corrections will reduce the errors in blue by 2% in some cases.

Electron Bombarded Charge Coupled Devices (EBCCDs) are a new hybrid image intensifier tube device that allows photoelectrons to be directly detected by a CCD placed as the tube anode. These devices have many significant advantages over traditional image intensified systems, due to their lower noise figure, high intra-scene dynamic range, and high signal to noise ratio. EBCCDs are not subject to some of the deleterious effects that plague traditional intensifiers including veiling glare, "chicken wire" patterns, and ion scintillation. Currently, there is not a standardized set of characterization methods used to measure the performance of these hybrid devices. Furthermore, the normal method of measuring device gain as a ratio of output current (measured as current through the anode substrate) to input current (as measured through the photocathode) does not apply to EBCCDs. This dissertation presents several new methods that have been developed to characterize in situ EBCCD tubes. The new characterization methods that have been developed are: (1) How to measure the actual gain of an EBCCD when operated as a CCD (normal operating mode), (2) How to measure the mean and variance of a single electron pulse height distribution when only multiple electron pulse height distribution data is available, (3) How to measure the spatially varying probability of secondary electron capture by the CCD potential wells, (4) How to measure the thickness of an aluminum overcoat using only optical measurements, (5) How to measure the gain variation due to aluminum thickness variations. These methods have been designed to enable characterization of the EBCCD even after it has been mounted in a camera. This will allow both tube and camera manufacturers to measure performance in a production setting. These new methods were employed, along with other standard measurement techniques, to characterize a commercially available EBCCD (Hamamatsu N7220) controlled by a camera designed by the author. Several figures of merit were measured as a function of accelerating potential including the gain, device signal to noise ratio, detective quantum efficiency, and noise figure. The tube MTF, radiometric sensitivity, aluminum thickness, dynamic range, and probability of secondary electron detection were also measured.

This dissertation addresses both fundamental aspects of Coulomb correlations in semiconductor quantum wells and more practical aspects of theoretical analysis of semiconductor optoelectronic devices. After introducing the subject, we present and evaluate a state-of-the-art theory of the third order coherent optical response of a semiconductor quantum well based on the Dynamics Controlled Truncation (DCT) scheme. Already in the third order (the so-called chi (3)) regime, semiconductors exhibit a number of many-body Coulomb correlation effects. Their manifestation in various multi-pulse experimental configurations, customarily used in ultrafast semiconductor spectroscopy, has been an important component of this thesis. Coherent optical effects in a semiconductor 3-band system based on the heavy-hole, light-hole and conduction bands were investigated. The quantum beats in the time-integrated differential transmission signal were analyzed and compared with experimental data obtained at the University of Iowa. Fundamental differences from corresponding quantum beats in atomic 3-level systems were found. Also, the analysis of experimental data (obtained at the University of Arizona) of the coupled heavy-hole-light-hole optical Stark shift revealed evidence of intervalence band coherences, an analog of Raman coherences in atomic 3-levels systems. A scheme for realization of electromagnetically-induced transparency (EIT) based on the interference of excitonic and biexcitonic coherences was proposed. Corresponding experiments performed at the University of Oregon showed indeed a considerable coherent reduction of excitonic absorption. Furthermore, an extension of the chi(3) analysis revealed an energy renormalization of the biexciton, in good agreement with the corresponding experiment. A microscopic analysis of polarization dynamics in time-resolved four-wave mixing signals was performed, revealing interesting implications for the biexciton dephasing in addition to the significance of many-body correlations. In the case of four-wave mixing in semiconductor microcavities, our theoretical analysis in conjunction with experimental data obtained at the University of Tokyo gave us indications for a significant shortcoming of the second Born approximation (2nd BA) applied to two-exciton Coulomb correlations in a thin semiconductor quantum well, in agreement with the general knowledge of the qualitative failure of the 2nd BA in systems with short-range interaction in two dimensions. We also analyzed a novel all-optical switching technique based on the nonlinear polarization rotation. Apart from identifying the many-particle processes relevant for the switch operation in the chi(3) regime, we proposed ways to further optimize the switch.

This dissertation describes advances in the operational stability and performance of polymer composites that used a new hole-transporting polymer matrix, PATPD. Stable operation is achieved when PATPD provides the transport manifold because it prevents the chromophores to act as hole-traps. Operational stability is combined with video-rate compatible response times and large photorefractive nonlinearities, comparable to those obtained with the commonly used hole-transporting polymer PVK. The advances obtained in understanding the impact of chromophore aggregation to the photorefractive properties of such composites will be presented in the framework of a two-trapping site mode. Numerical simulations of the photogenerated current transients and the sensitizer anion build-up will reveal the intricate nature of the trap dynamics when chromophore aggregates can act as hole-traps in a material. Finally, the photorefractive properties of hybrid polymer composites sensitized with CdSe nanoparticles, that currently define the state-of-the-art for the photorefractive performance of this kind of materials, will be presented. The operational stability of hybrid composites is presented for the first time and the limitations to its performance will be analyzed.

Super-resolution is defined as the ability to algorithmically or physically form an image with meaningful spatial frequency content at spatial frequencies for which the optical instrument has an optical transfer function equal to zero. Historically, the method of least-squares has played a significant role in numerous estimation problems including the super-resolution problem. A viable alternative for the recovery of non-negative signals is the minimum cross-entropy principle. This principle is a generalization of minimum discrimination information in statistics and information theory. In the first part of the dissertation, various minimum cross-entropy methods for super-resolution are presented. Alternating Projections, a special case of which is the class of Expectation-Maximization (EM) algorithms, and Picard-type iterations are employed in our investigations. A cross-entropic Projection-Onto-Convex-Sets (POCS) formulation is developed to provide an alternate interpretation of the minimum cross-entropy based EM-type algorithms. This interpretation provides a theoretical basis for including some a priori object constraints in iterative super-resolution algorithms. The performance of signal recovery algorithms is dependent on the sparsity of the signal. This fact has been observed empirically and theoretically by several researchers. Indeed, the Gerchberg-Papoulis (GP) algorithm achieves bandwidth extrapolation primarily from the finite spatial extent a priori knowledge, a special form of signal sparsity. Unfortunately, in real-world applications, objects are rarely sparse. In the second part of the dissertation, some approximately sparse representations of signals, viz., background-foreground, trend-fluctuations and wavelet representations are proposed to circumvent the sparsity requirement. Multigrid methods and wavelet decompositions are two closely related concepts. Multigrid methods were proposed to improve the convergence rates of iterative smoothers by appending corrections from coarse grids to an approximate estimate at the fine grid. Wavelet representation schemes, on the other hand, show great promise in alternatively representing an object as sparse components. A wavelet-subspace based multigrid formulation for recovery of nonsparse objects is proposed. A unified space-decomposition formulation that ties related concepts found in varied application areas, viz., Grenander's method of sieves in statistical inference, intrinsic correlation functions in astronomy, method of resolution kernels, wavelet-based space-decompositions, space-decompositions in multigrid methods etc., is presented.

The ability to conduct in-flight, absolute radiometric calibrations of ocean color sensors will determine their usefulness in the decade to come. On-board calibration systems are often integrated into the overall design of such sensors and have claimed uncertainty levels below 5%. Independent means of system calibration are needed to confirm that the sensor is accurately calibrated. Vicarious (i.e. ground-referencing) methods are an attractive way to conduct this verification. This research describes the development of in-flight, absolute radiometric calibration methods which reference dark (i.e. low-reflectance) sites. The high sensitivity of ocean color sensors results in saturation over bright surfaces. Low-reflectance targets, such as water bodies, are therefore required for their vicarious calibration. Sensitivity analyses of the reflectance-based and radiance-based techniques, when applied to a water target, are performed. Uncertainties in atmospheric parameters, surface reflectance measurements, and instrument characterization are evaluated for calibrations of a representative ocean color sensor. For a viewing geometry near the sun glint region, reflectance-based uncertainties range between 1.6% and 2.3% for visible and near-IR wavelengths; radiance-based uncertainties range between 6.8% and 20.5%. These studies indicate that better characterization of aerosol parameters is desired and that radiometer pointing accuracy must be improved to make the radiance-based method useful. The uncertainty estimates are evaluated using data from a field campaign at Lake Tahoe in June, 1995. This lake is located on the California-Nevada border and has optical characteristics similar to oceanic waters. Aircraft-based radiance data and surface measurements of water reflectance are used to calibrate visible and near infrared bands of the Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS). The vicariously-derived calibration coefficients are compared to those obtained from a preflight calibration of AVIRIS. The results agree at the 0.3-7.7% level for the reflectance-based technique, which is within the believed method uncertainties. Finally, as a consequence of this research, the testing and refinement of radiative transfer codes applicable to oceanic environments is accomplished. These modifications lead to an improvement in the prediction of top-of-atmosphere radiances over water targets.

As the field of remote sensing continues to grow with the launches of many new and complex satellite sensors in the next year, the ability to provide absolute calibration of these sensors becomes paramount for the many environmental studies proposed. In particular, temporal studies that monitor global changes in atmospheric constituents, ocean and terrestrial temperatures, and vegetation require that changes in the sensor itself, over the period of the study, be understood so that the data may be corrected. Numerous studies have established that satellite sensors change in orbit with respect to preflight calibration, in some cases, up to 20% or more over periods of three years. This research describes the development of an improved cross-calibration method of on-orbit satellite sensor radiometric calibration. The objective of the cross-calibration method is to transfer one sensor's calibration to another sensor which is typically difficult or expensive to calibrate with other methods. The cross-calibration method is relatively inexpensive to apply, and therefore there was a strong incentive to improve the application of the method and the understanding of the uncertainties associated with the method. The primary effort in this work has been the development of a cross-calibration software program which provides the means to easily perform end-to-end cross-calibrations. The program allows for a multiplicity of sites to be run, provides a search mechanism in order to identify calibration sites with particular characteristics, and contains an extensive error analysis capability. As part of this work, a search for acceptable cross-calibration sites was also performed which would allow a reduction in uncertainties of the method. Calibrations of five different sensor band pairs using System Pour l'Observation de la Terre (SPOT) 3, Landsat Thematic Mapper, and Advanced Very High Resolution Radiometer (AVHRR) sensors are performed. Very good results are obtained when the results are compared with other more expensive calibration methods, and the calibrations yielded uncertainties lower than reported in previous work.

Super-resolution is the ability of a restoration algorithm to restore meaningful spatial frequency content beyond the diffraction limit of the imaging system. The Gerchberg-Papoulis (GP) algorithm is one of the most celebrated algorithms for super-resolution. The GP algorithm is conceptually simple and demonstrates the importance of using a priori information in the formation of the object estimate. In the first part of this dissertation the continuous GP algorithm is discussed in detail and shown to be a projection on convex sets algorithm. The discrete GP algorithm is shown to converge in the exactly-, over- and under-determined cases. A direct formula for the computation of the estimate at the kth iteration and at convergence is given. This analysis of the discrete GP algorithm sets the stage to connect super-resolution to error-correction codes. Reed-Solomon codes are used for error-correction in magnetic recording devices, compact disk players and by NASA for space communications. Reed-Solomon codes have a very simple description when analyzed with the Fourier transform. This signal processing approach to error-correction codes allows the error-correction problem to be compared with the super-resolution problem. The GP algorithm for super-resolution is shown to be equivalent to the correction of errors with a Reed-Solomon code over an erasure channel. The Restoration from Magnitude (RFM) problem seeks to recover a signal from the magnitude of the spectrum. This problem has applications to imaging through a turbulent atmosphere. The turbulent atmosphere causes localized changes in the index of refraction and introduces different phase delays in the data collected. Synthetic aperture radar (SAR) and hyperspectral imaging systems are capable of simultaneously recording multiple images of different polarizations or wavelengths. Each of these images will experience the same turbulent atmosphere and have a common phase distortion. A projection based restoration algorithm for the simultaneous restoration of pairs of images experiencing a common phase distortion is presented.