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Astigmatism and Pseudoaccommodation in Pseudophakic Eyes
noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved
Progressive Transient Photon Beams
In this work we introduce a novel algorithm for transient rendering in
participating media. Our method is consistent, robust, and is able to generate
animations of time-resolved light transport featuring complex caustic light
paths in media. We base our method on the observation that the spatial
continuity provides an increased coverage of the temporal domain, and
generalize photon beams to transient-state. We extend the beam steady-state
radiance estimates to include the temporal domain. Then, we develop a
progressive version of spatio-temporal density estimations, that converges to
the correct solution with finite memory requirements by iteratively averaging
several realizations of independent renders with a progressively reduced kernel
bandwidth. We derive the optimal convergence rates accounting for space and
time kernels, and demonstrate our method against previous consistent transient
rendering methods for participating media
Reports about 8 selected benchmark cases of model hierarchies : Deliverable number: D5.1 - Version 0.1
Based on the multitude of industrial applications, benchmarks for model hierarchies will be created that will form a basis for the interdisciplinary research and for the training programme. These will be equipped with publically available data and will be used for training in modelling, model testing, reduced order modelling, error estimation, efficiency optimization in algorithmic approaches, and testing of the generated MSO/MOR software. The present document includes the description about the selection of (at least) eight benchmark cases of model hierarchies.EC/H2020/765374/EU/Reduced Order Modelling, Simulation and Optimization of Coupled Systems/ROMSO
Determining the Phase and Amplitude Distortion of a Wavefront using a Plenoptic Sensor
We have designed a plenoptic sensor to retrieve phase and amplitude changes
resulting from a laser beam's propagation through atmospheric turbulence.
Compared with the commonly restricted domain of (-pi, pi) in phase
reconstruction by interferometers, the reconstructed phase obtained by the
plenoptic sensors can be continuous up to a multiple of 2pi. When compared with
conventional Shack-Hartmann sensors, ambiguities caused by interference or low
intensity, such as branch points and branch cuts, are less likely to happen and
can be adaptively avoided by our reconstruction algorithm. In the design of our
plenoptic sensor, we modified the fundamental structure of a light field camera
into a mini Keplerian telescope array by accurately cascading the back focal
plane of its object lens with a microlens array's front focal plane and
matching the numerical aperture of both components. Unlike light field cameras
designed for incoherent imaging purposes, our plenoptic sensor operates on the
complex amplitude of the incident beam and distributes it into a matrix of
images that are simpler and less subject to interference than a global image of
the beam. Then, with the proposed reconstruction algorithms, the plenoptic
sensor is able to reconstruct the wavefront and a phase screen at an
appropriate depth in the field that causes the equivalent distortion on the
beam. The reconstructed results can be used to guide adaptive optics systems in
directing beam propagation through atmospheric turbulence. In this paper we
will show the theoretical analysis and experimental results obtained with the
plenoptic sensor and its reconstruction algorithms.Comment: This article has been accepted by JOSA
Phase Shaping In The Infrared By Planar Quasi-periodic Surfaces Comprised Of Sub-wavelength Elements
Reflectarrays are passive quasi-periodic sub-wavelength antenna arrays designed for discrete reflected phase manipulation at each individual antenna element making up the array. By spatially varying the phase response of the antenna array, reflectarrays allow a planar surface to impress a non-planar phasefront upon re-radiation. Such devices have become commonplace at radio frequencies. In this dissertation, they are demonstrated in the infrared for the first time--at frequencies as high as 194 THz. Relevant aspects of computational electromagnetic modeling are explored, to yield design procedures optimized for these high frequencies. Modeling is also utilized to demonstrate the phase response of a generalized metallic patch resonator in terms of its dependence on element dimensions, surrounding materials, angle of incidence, and frequency. The impact of realistic dispersion of the real and imaginary parts of the metallic permittivity on the magnitude and bandwidth of the resonance behavior is thoroughly investigated. Several single-phase reflectarrays are fabricated and measurement techniques are developed for evaluating these surfaces. In all of these cases, there is excellent agreement between the computational model results and the measured device characteristics. With accurate modeling and measurement, it is possible to proceed to explore some specific device architectures appropriate for focusing reflectarrays, including binary-phase and phase-incremental approaches. Image quality aspects of these focusing reflectarrays are considered from geometrical and chromatic-aberration perspectives. The dissertation concludes by briefly considering two additional analogous devices--the transmitarray for tailoring transmissive phase response, and the emitarray for angular control of thermally emitted radiation
Determining the Influence of Environment and Minimizing Residual Roughness in Laser Corneal Refractive Surgery
Aims: This dissertation deals with multiple topics, with a global aim of determining the influence of environment and minimizing residual roughness in laser corneal refractive surgery. The multiple topics under consideration are listed below:
•TOPIC A: To analyze the effect of seasonal changes in PMMA Performance using the SCHWIND AMARIS laser system
•TOPIC B: To analyze impact of various humidity and temperature settings on excimer laser ablation of PET, PMMA and porcine corneal tissue
•TOPIC C: To analyze the impact of residual roughness after corneal ablation in perception and vision
•TOPIC D: To outline a rigorous simulation model for simulating shot-by-shot ablation process. Furthermore, to simulate the impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap and lattice geometry on ablation smoothness.
•TOPIC E: To test the impact of laser beam truncation, dithering, and jitter on residual roughness after PMMA ablations, using a close-to-Gaussian beam profile.
Methods:
TOPIC A: By analyzing PMMA and PET ablation performance by a large series of AMARIS laser systems (Schwind eye-tech solutions, Germany) inside a climate controlled environment, the influence purely coming from the seasonal changes was investigated in a large scale retrospective cross sectional review. Seasonal outcomes were evaluated in terms of PMMA and PET Performance stratified for every month in a year, as well as stratified for each season in a year.
TOPIC B: A Study was conducted using AMARIS system placed inside a climate chamber. Ablations were performed on PET, PMMA and porcine cornea. Impact of wide range of temperature (~18°C to ~30°C) and relative humidity (~25% to ~80%) on laser ablation outcomes was tested using nine climate test settings. Multiple linear regression was performed using least square method with predictive factors: Temperature, Relative Humidity, Time stamp. Influence of climate settings was modelled for Pulse Energy, Pulse Fluence, ablation efficiency on PMMA and porcine cornea tissue.
TOPIC C: The Indiana Retinal Image Simulator (IRIS) was used to simulate the polychromatic retinal image. Using patient-specific Zernike coefficients and pupil diameter, the impact of different levels of chromatic aberrations was calculated. Corneal roughness was modeled via both random and filtered noise, using distinct pre-calculated higher order Zernike coefficient terms. The outcome measures for the simulation were simulated retinal image, Strehl Ratio and Visual Strehl Ratio computed in frequency domain. The impact of varying degree of roughness, spatial frequency of the roughness, and pupil dilation was analyzed on these outcome measures.
TOPIC D: Given the super Gaussian order, the theoretical beam profile was determined following Lambert-Beer model. The intensity beam profile originating from an excimer laser was measured with a beam profiler camera. For both, the measured and theoretical, beam profiles, two spot geometries (round and square spots) were considered, and two types of lattices (reticular and triangular) were simulated with varying spot overlaps and ablated material (cornea or PMMA). The roughness in ablation was determined by the root-mean-square per square root of layer depth.
TOPIC E: A study was conducted using a modified AMARIS system. For the PMMA ablations, two configurations (with a 0.7mm pinhole and 0.75mJ and without pinhole and 0.9mJ (for fluences of 329mJ/cm2 and 317mJ/cm2 and corneal spot volumes of 174pl and 188pl)) were considered, along with two types of lattices (with and without ordered dithering to select the optimum pulse positions), and two types of spot placement (with and without jitter). Real ablations on PMMA (ranging from -12D to +6D with and without astigmatism) completed the study setup. The effect of the 2x2x2 different configurations was analyzed based on the roughness in ablation estimated from the root mean square error in ablation.
Results:
TOPIC A: The seasons winter and summer showed statistical significant variations with respect to the global values for all the tested parameters except the nominal number of laser pulses for high and low fluence setting. The metric technical performance of the analyzed systems showed a stronger PMMA ablation performance in summer time compared to a weaker performance in the winter time, with the maximum seasonal deviation of 6%. The results were consistently confirmed in seasonal as well as monthly analyses.
TOPIC B: Temperature changes did not affect laser pulse energy, pulse fluence (PET), and ablation efficiency (on PMMA or porcine corneal tissue) significantly. Changes in relative humidity were more critical and significantly affected laser pulse energy, high fluence and low fluence. Opposite trend was observed between the ablation performance on PMMA and porcine cornea.
TOPIC C: In case of a constant roughness term, reducing the pupil size resulted in improved outcome measures and simulated retinal image. The calculated image quality metrics deteriorated dramatically with increasing roughness. Clear distinction was observed in outcome measures for corneal roughness simulated as random noise compared to filtered noise, further influenced by the spatial frequency of filtered noise.
TOPIC D: Truncating the beam profile increased the roughness in ablation, Gaussian profiles theoretically resulted in smoother ablations, round spot geometries produced lower roughness in ablation compared to square geometry, triangular lattices theoretically produced lower roughness in ablation compared to the reticular lattice, theoretically modelled beam profiles showed lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tend to be lower than on human cornea. For given input parameters, proper optimum parameters for minimizing the roughness has been found.
TOPIC E: Truncation of the beam was negatively associated to a higher level of residual roughness; ordered dithering to select the optimum pulse positions was positively associated to a lower level of residual roughness; jitter was negatively associated to a higher level of residual roughness. The effect of dithering was the largest, followed by truncation, and jitter had the lowest impact on results.
Conclusions: The large scale retrospective cross sectional study presented in this work, demonstrated a cyclic winter-summer variation in PMMA ablation using the AMARIS lasers. These seasonal variations were further substantiated with the experiments conducted in the climate chamber, over a wide range of temperature and humidity. Temperature changes did not affect laser pulse energy, pulse fluence, and ablation efficiency (on PMMA or porcine corneal tissue) significantly. However, changes in relative humidity were more critical and significantly affected laser pulse energy, high fluence and low fluence. The proposed well-fitting multi-linear model can be utilized for compensation of temperature and humidity changes on ablation efficiency. The relationship between calibration materials like PMMA and corneal tissue shall be analyzed cautiously before designing the calibration routine, in order to obtain optimum outcomes with minimum deviations. Despite its limitations, the simple and robust method proposed here for quantifying the influence of post-ablation roughness on vision and perception, can be utilized in different applications. From the simulations of the shot-by-shot ablation process, a theoretical proper optimum configuration was found for minimizing the roughness in ablation for defined input parameters. The PMMA experiments confirmed the theoretical proper optimum settings in real world conditions. The results and improvements derived out of this work can be directly applied to the laser systems for corneal refractive surgery, to help reduce the complications and occurrence of adverse events during and after refractive surgery, and improve the short term and long term postoperative clinical outcomes
Computational Light Transport for Forward and Inverse Problems.
El transporte de luz computacional comprende todas las técnicas usadas para calcular el flujo de luz en una escena virtual. Su uso es ubicuo en distintas aplicaciones, desde entretenimiento y publicidad, hasta diseño de producto, ingenierÃa y arquitectura, incluyendo el generar datos validados para técnicas basadas en imagen por ordenador. Sin embargo, simular el transporte de luz de manera precisa es un proceso costoso. Como consecuencia, hay que establecer un balance entre la fidelidad de la simulación fÃsica y su coste computacional. Por ejemplo, es común asumir óptica geométrica o una velocidad de propagación de la luz infinita, o simplificar los modelos de reflectancia ignorando ciertos fenómenos. En esta tesis introducimos varias contribuciones a la simulación del transporte de luz, dirigidas tanto a mejorar la eficiencia del cálculo de la misma, como a expandir el rango de sus aplicaciones prácticas. Prestamos especial atención a remover la asunción de una velocidad de propagación infinita, generalizando el transporte de luz a su estado transitorio. Respecto a la mejora de eficiencia, presentamos un método para calcular el flujo de luz que incide directamente desde luminarias en un sistema de generación de imágenes por Monte Carlo, reduciendo significativamente la variancia de las imágenes resultantes usando el mismo tiempo de ejecución. Asimismo, introducimos una técnica basada en estimación de densidad en el estado transitorio, que permite reusar mejor las muestras temporales en un medio parcipativo. En el dominio de las aplicaciones, también introducimos dos nuevos usos del transporte de luz: Un modelo para simular un tipo especial de pigmentos gonicromáticos que exhiben apariencia perlescente, con el objetivo de proveer una forma de edición intuitiva para manufactura, y una técnica de imagen sin lÃnea de visión directa usando información del tiempo de vuelo de la luz, construida sobre un modelo de propagación de la luz basado en ondas.<br /
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