Dissertations / Theses on the topic 'Wavefront'
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1
FREISCHLAD, KLAUS REINHARD. "WAVEFRONT SENSING BY HETERODYNE SHEARING INTERFEROMETRY (WAVEFRONT RECONSTRUCTION)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183952.
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The operation of a grating lateral shear heterodyne interferometer as a wavefront sensor for atmospherically perturbed wavefronts is analyzed. A novel wavefront sensor design is given and its feasibility is proven by laboratory experiments. The applications in mind are closed-loop active optical systems for compensating atmospheric perturbations and open-loop atmospheric wavefront measuring device. The optical properties of the turbulent atmosphere are summed up and the resulting wavefront sensor requirements are given. Among them are the property of sell-referencing, high white light efficiency, independence of scintillation effects, and high spatial and temporal sampling rates. Then the general heterodyne grating shearing interferometer is introduced. A description of the phase measurement by the heterodyne process in the frequency domain has been derived. The heterodyne process is interpreted as convolutions of the signal with a pair of filter functions, which isolate a particular harmonic term of the signal and provide its phase. The representation of the convolutions in the frequency domain provides an elegant way to analyse the systematic errors of the heterodyning with general, non-sinusoidal signals. Also the random phase errors of the heterodyne process have been determined using Gaussian error propagation. An algorithm is derived to carry out the wavefront reconstructions from the measured differences on a square array of discrete data points. It is based on a modal expansion in complex exponentials, leading to a simple filtering operation in the spatial frequency domain. The algorithm provides unbiased reconstructions over the finite data set. It has minimal error propagation in a least squares sense. It is computationally efficient in that the number of operations required for a reconstruction is approximately proportional to the number of wavefront points, if a Fast-Fourier-Transform algorithm is used. Finally, a compact wavefront sensor design is described fulfilling the requirements posed by the turbulent atmosphere. It determines wavefronts at 24 by 24 points at a sampling rate of 60 Hz. A rms-wavefront error of better than λ/20 can be achieved with astronomical light sources of sixth stellar magnitude. Laboratory experiments proved the feasibility of the design.
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Mahajan, Virendra N., and Eva Acosta. "Wavefront analysis from its slope data." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626489.
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In the aberration analysis of a wavefront over a certain domain, the polynomials that are orthogonal over and represent balanced wave aberrations for this domain are used. For example, Zernike circle polynomials are used for the analysis of a circular wavefront. Similarly, the annular polynomials are used to analyze the annular wavefronts for systems with annular pupils, as in a rotationally symmetric two-mirror system, such as the Hubble space telescope. However, when the data available for analysis are the slopes of a wavefront, as, for example, in a Shack-Hartmann sensor, we can integrate the slope data to obtain the wavefront data, and then use the orthogonal polynomials to obtain the aberration coefficients. An alternative is to find vector functions that are orthogonal to the gradients of the wavefront polynomials, and obtain the aberration coefficients directly as the inner products of these functions with the slope data. In this paper, we show that an infinite number of vector functions can be obtained in this manner. We show further that the vector functions that are irrotational are unique and propagate minimum uncorrelated additive random noise from the slope data to the aberration coefficients.
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Lundström, Linda. "Wavefront Aberrations and Peripheral Vision." Doctoral thesis, KTH, Tillämpad fysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4385.
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Failing eyesight causes a dramatic change in life. The aim of this project is to help people with large central visual field loss to better utilize their remaining vision. Central visual field loss means that the person has to rely on peripheral vision since the direct vision is lost, often due to a dysfunctional macula. In these cases, a full restoration of vision would require replacement or repair of the damaged retinal tissue, which is not yet possible. Instead, the present study seeks to improve peripheral vision by enhancing the image quality on the remaining functional part of the retina by optical corrections. The off-axis optics of the human eye often suffers from large optical errors, which together with the lower sampling density of the retina explain the limited visual function in the periphery. The dominating aberrations are field curvature and oblique astigmatism, which induce an effective eccentric refractive error. However, the irregular character of the aberrations and the limited neural function in the periphery will make it difficult to find the optimal refractive correction; the conventional subjective refraction, for example, is not suitable for subjects with large central visual field loss. Within the work of this thesis a Hartmann-Shack wavefront sensor has been constructed for oblique aberration measurements. Wavefront sensing is an objective method to assess detailed information about the optical errors in the human eye. Theory and methods have been developed to allow accurate off-axis measurements of the large aberrations, enable eccentric fixation, and handle the elliptical pupil. The study has mainly concentrated on sphero-cylindrical correction of peripheral vision. Peripheral resolution and detection acuity thresholds have been evaluated for seven subjects with central visual field loss and ten control subjects with normal vision. Five of the subjects with field loss showed improved resolution acuity with eccentric refractive correction compared to their habitual central correction, whereas little change was found for the control subjects. These results demonstrate that correction of peripheral optical errors can be beneficial to people with large central visual field loss in situations where a normal healthy eye does not experience any improvements. In conclusion, it is worthwhile to investigate the peripheral refractive errors in low-vision rehabilitation of central visual field loss and prescribe spectacle correction when those errors are large.QC 20100809
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Lundström, Linda. "Wavefront aberrations and peripheral vision /." Stockholm : Department of Applied Physics, Royal Institute of Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4385.
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Chew, Theam Yong. "Wavefront sensors in Adaptive Optics." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/1645.
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Atmospheric turbulence limits the resolving power of astronomical telescopes by distorting
the paths of light between distant objects of interest and the imaging camera at the telescope.
After many light-years of travel, passing through the turbulence in that last 100km of a
photon’s journey results in a blurred image in the telescope, no less than 1” (arc-second)
in width. To achieve higher resolutions, corresponding to smaller image widths, various
methods have been proposed with varying degrees of effectiveness and practicality.
Space telescopes avoid atmospheric turbulence completely and are limited in resolution
solely by the size of their mirror apertures. However, the design and maintenance cost of
space telescopes, which increases prohibitively with size, has limited the number of space
telescopes deployed for astronomical imaging purposes. Ground based telescopes can be
built larger and more cheaply, so atmospheric compensation schemes using adaptive optical
cancellation mirrors can be a cheaper substitute for space telescopes.
Adaptive optics is referred to here as the use of electronic control of optical component to
modify the phase of an incident ray within an optical system like an imaging telescope. Fast
adaptive optics systems operating in real-time can be used to correct the optical aberrations
introduced by atmospheric turbulence. To compensate those aberrations, they must first
be measured using a wavefront sensor. The wavefront estimate from the wavefront sensor
can then be applied, in a closed-loop system, to a deformable mirror to compensate the
incoming wavefront.
Many wavefront sensors have been proposed and are in used today in adaptive optics and
atmospheric turbulence measurement systems. Experimental results comparing the performance
of wavefront sensors have also been published. However, little detailed analyses
of the fundamental similarities and differences between the wavefront sensors have been
performed.
This study concentrates on fourmain types of wavefront sensors, namely the Shack-Hartmann,
pyramid, geometric, and the curvature wavefront sensors, and attempts to unify their description
within a common framework. The quad-cell is a wavefront slope detector and is
first examined as it lays the groundwork for analysing the Shack-Hartmann and pyramid
wavefront sensors.
The quad-cell slope detector is examined, and a new measure of performance based on the
Strehl ratio of the focal plane image is adopted. The quad-cell performance based on the
Strehl ratio is compared using simulations against the Cramer-Rao bound, an information
theoretic or statistical limit, and a polynomial approximation. The effects of quad-cell
modulation, its relationship to extended objects, and the effect on performance are also
examined briefly.
In the Shack-Hartmann and pyramid wavefront sensor, a strong duality in the imaging and
aperture planes exists, allowing for comparison of the performance of the two wavefront
sensors. Both sensors subdivide the input wavefront into smaller regions, and measure the
local slope. They are equivalent in every way except for the order in which the subdivision
and slope measurements were carried out. We show that this crucial difference leads to a
theoretically higher performance from the pyramid wavefront sensor. We also presented
simulations showing the trade-off between sensor precision and resolution.
The geometric wavefront sensor can be considered to be an improved curvature wavefront
sensor as it uses a more accurate algorithm based on geometric optics to estimate the wavefront.
The algorithm is relatively new and has not found application in operating adaptive
optics systems. Further analysis of the noise propagation in the algorithm, sensor resolution,
and precision is presented. We also made some observations on the implementation
of the geometric wavefront sensor based on image recovery through projections.
6
Campbell, Heather Isla. "Generalised Phase Diversity wavefront sensing." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/167.
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Pape, Ulrich v. "Wavefront sensing in the human eye." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=963766163.
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Muyo, Nieto Gonzalo D. "Principles and applications of wavefront coding." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/2043.
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The aim of the work reported in this thesis was to investigate the physical principles and potential applications of wavefront coding. This technique enables extended depth of field and greatly reduced sensitivity to defocus-related and higher-order aberrations whilst maintaining diffraction-limited resolution in incoherent imaging systems. Wavefront· coding involves the introduction of an asymmetric refractive mask close to the aperture stop so as to encode the image with a specific point spread function that, when combined with decoding of the recorded image, can enable accurate image acquisition even in the presence of aberrations. In practical imaging systems, this enhancement is subject to a range of constraints and limitations which have been neglected in previous works. We show that although-wavefront coding has sometimes been presented as a panacea, it is more realistic to consider it as an additional parameter in the optimisation process. This research explores the trade offs involved in the application of wavefront coding to lowcost imaging systems for use in t,he thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems. Some of the original contributions of this work include the design of new phase masks, a new understanding of the fundamental physical principles in terms of the decomposition of the optical transfer function, appraisal of the restoration issues (detector sampling, noise amplification and artefacts in the digitally processed image) and the design and manufacture of a wavefront-coded infrared singlet.
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Weddell, Stephen John. "Optical Wavefront Prediction with Reservoir Computing." Thesis, University of Canterbury. Electrical and Computer Engineering, 2010. http://hdl.handle.net/10092/4070.
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Over the last four decades there has been considerable research in the improvement of imaging exo-atmospheric objects through air turbulence from ground-based instruments. Whilst such research was initially motivated for military purposes, the benefits to the astronomical community have been significant. A key topic in this research is isoplanatism. The isoplanatic angle is an angular limit that separates two point-source objects, where if independent measurements of wavefront perturbations were obtained from each source, the wavefront distortion would be considered equivalent. In classical adaptive optics, perturbations from a point-source reference, such as a bright, natural guide star, are used to partially negate perturbations distorting an image of a fainter, nearby science object.
Various techniques, such as atmospheric tomography, maximum a posteriori (MAP), and parameterised modelling, have been used to estimate wavefront perturbations when the distortion function is spatially variant, i.e., angular separations exceed the isoplanatic angle, θ₀, where θ₀ ≈ 10 μrad for mild distortion at visual wavelengths. However, the effectiveness of such techniques is also dependent on knowledge a priori of turbulence profiles and configuration data.
This dissertation describes a new method used to estimate the eigenvalues that comprise wavefront perturbations over a wide, spatial field. To help reduce dependency on prior knowledge for specific configurations, machine learning is used with a recurrent neural network trained using a posteriori wavefront ensembles from multiple point-source objects. Using a spatiotemporal framework for prediction, the eigenvalues, in terms of Zernike polynomials, are used to reconstruct the spatially-variant, point spread function (SVPSF) for image restoration. The overall requirement is to counter the adverse effects of atmospheric turbulence on the images of extended astronomical objects. The method outlined in this thesis combines optical wavefront sensing using multiple natural guide stars, with a reservoir-based, artificial neural network. The network is used to predict aberrations caused by atmospheric turbulence that degrade the images of faint science objects.
A modified geometric wavefront sensor was used to simultaneously measure phase perturbations from multiple, point-source reference objects in the pupil. A specialised recurrent neural network (RNN) was used to learn the spatiotemporal effects of phase perturbations measured from several source references. Modal expansions, in terms of Zernike coefficients, were used to build time-series ensembles that defined wavefront maps of point-source reference objects. The ensembles were used to firstly train an RNN by applying a spatiotemporal training algorithm, and secondly, new data ensembles presented to the trained RNN were used to estimate the wavefront map of science objects over a wide field. Both simulations and experiments were used to evaluate this method.
The results of this study showed that by employing three or more source references over an angular separation of 24 μrad from a target, and given mild turbulence with Fried coherence length of 20 cm, the normalised mean squared error of low-order Zernike modes could be estimated to within 0.086.
A key benefit in estimating phase perturbations using a time-series of short exposure point-spread functions (PSFs) is that it is then possible to determine the long exposure PSF. Based on the summation of successive, corrected, short-exposure frames, high resolution images of the science object can be obtained. The method was shown to predict a contiguous series of short exposure aberrations, as a phase screen was moved over a simulated aperture. By qualifying temporal decorrelation of atmospheric turbulence, in terms of Taylor's hypothesis, long exposure estimates of the PSF were obtained.
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Curatu, Costin. "Wavefront Sensor for Eye Aberrations Measurements." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2274.
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Ocular wavefront sensing is vital to improving our understanding of the human eye and to developing advanced vision correction methods, such as adaptive optics, customized contact lenses, and customized laser refractive surgery. It is also a necessary technique for high-resolution imaging of the retina. The most commonly used wavefront sensing method is based on the Shack-Hartmann wavefront sensor. Since Junzhong Liang's first application of Shack-Hartmann wavefront sensing for the human eye in 1994, the method has quickly gained acceptance and popularity in the ophthalmic industry. Several commercial Shack-Hartmann eye aberrometers are currently available. While the existing aberrometers offer reasonable measurement accuracy and reproducibility, they do have a limited dynamic range. Although rare, highly aberrated eyes do exists (corneal transplant, keratoconus, post-lasik) that cannot be measured with the existing devices. Clinicians as well as optical engineers agree that there is room for improvement in the performance of these devices "Although the optical aberrations of normal eyes have been studied by the Shack-Hartmann technique, little is known about the optical imperfections of abnormal eyes. Furthermore, it is not obvious that current Shack-Hartmann aberrometers are robust enough to successfully measure clinically abnormal eyes of poor optical quality" Larry Thibos, School of Optometry, Indiana University. The ultimate goal for ophthalmic aberrometers and the main objective of this work is to increase the dynamic range of the wavefront sensor without sacrificing its sensitivity or accuracy. In this dissertation, we attempt to review and integrate knowledge and techniques from previous studies as well as to propose our own analytical approach to optimizing the optical design of the sensor in order to achieve the desired dynamic range. We present the underlying theory that governs the relationship between the performance metrics of the sensor: dynamic range, sensitivity, spatial resolution, and accuracy. We study the design constraints and trade-offs and present our system optimization method in detail. To validate the conceptual approach, a complex simulation model was developed. The comprehensive model was able to predict the performance of the sensor as a function of system design parameters, for a wide variety of ocular wavefronts. This simulation model did confirm the results obtained with our analytical approach. The simulator itself can now be used as a standalone tool for other Shack-Hartmann sensor designs. Finally, we were able to validate our theoretical work by designing and building an experimental prototype. We present some of the more practical design aspects, such as illumination choices and tolerance analysis methods. The prototype validated the conceptual approach used in the design and was able to demonstrate a vast increase in dynamic range while maintaining accurate and repeatable measurements.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Koukourakis, N., B. Fregin, L. Büttner, and J. W. Czarske. "Adaptive wavefront shaping for flowfield measurements." SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35058.
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In this contribution we use wavefront shaping approaches for image correlation based flow-field measurements for the first time. Aberrations introduced by a single phase boundary in the detection beam path were explored. Variations of the optical path-length result in strong errors in position allocation and thus to an enhancement of the measurement uncertainty of the velocity. Our results show that the usage of wavefront shaping enables to reduce these errors and to strongly improve the quality of image correlation based flow-field measurements. First experimental and simulated results underline the importance of these approaches.
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Mohanty, Siddharth. "Autotuning wavefront patterns for heterogeneous architectures." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10557.
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Manual tuning of applications for heterogeneous parallel systems is tedious and complex. Optimizations are often not portable, and the whole process must be repeated when moving to a new system, or sometimes even to a different problem size. Pattern based parallel programming models were originally designed to provide programmers with an abstract layer, hiding tedious parallel boilerplate code, and allowing a focus on only application specific issues. However, the constrained algorithmic model associated with each pattern also enables the creation of pattern-specific optimization strategies. These can capture more complex variations than would be accessible by analysis of equivalent unstructured source code. These variations create complex optimization spaces. Machine learning offers well established techniques for exploring such spaces. In this thesis we use machine learning to create autotuning strategies for heterogeneous parallel implementations of applications which follow the wavefront pattern. In a wavefront, computation starts from one corner of the problem grid and proceeds diagonally like a wave to the opposite corner in either two or three dimensions. Our framework partitions and optimizes the work created by these applications across systems comprising multicore CPUs and multiple GPU accelerators. The tuning opportunities for a wavefront include controlling the amount of computation to be offloaded onto GPU accelerators, choosing the number of CPU and GPU threads to process tasks, tiling for both CPU and GPU memory structures, and trading redundant halo computation against communication for multiple GPUs. Our exhaustive search of the problem space shows that these parameters are very sensitive to the combination of architecture, wavefront instance and problem size. We design and investigate a family of autotuning strategies, targeting single and multiple CPU + GPU systems, and both two and three dimensional wavefront instances. These yield an average of 87% of the performance found by offline exhaustive search, with up to 99% in some cases.
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Williby, Gregory Allen. "Transmitted wavefront testing of complex optics." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289995.
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The advancement of optical systems arises from furthering at least one of the three fields of optical development: design, fabrication, and testing. One example of such advancement is the growth in customization of contact lenses, which is occurring in part due to advances in testing. Due to the diverse quantities that can be derived from it, the transmitted wavefront is the tested parameter. There are a number of tests that can evaluate a transmitted wavefront, including moire deflectometry, Shack-Hartmann wavefront sensing, and interferometry. Interferometry is preferred for its sensitivity and spatial resolution. The dynamic range issue is mitigated by the required immersion of the contact lenses in saline due to the complex nature of the lens material. The partial index-match between the lens and surrounding saline reduces the measured power of the lens and enables testing in an absolute, or non-null, configuration. Absolute testing allows for the generation of ophthalmic prescriptions and power maps from the transmitted wavefront. Designing a non-null interferometer is based on three principles. The transmitted light must be collected, the resulting interference must be resolved, and the imaged wavefront must be calibrated. The first two principles are fulfilled by proper choices for the imaging lens and detector. Calibration comes from removing the wavefront-dependent induced aberrations via reverse raytracing. Reverse raytracing demands an accurate model of the interferometer. With such a model, theoretical wavefronts can be produced and compared to measured wavefronts. The difference between measured and modeled wavefronts quantifies the answer to the fundamental question in transmitted wavefront testing: does the optic perform as desired? Immersion in index-matching fluid provides an adjustable increase in the dynamic range of the interferometer. The increase comes at the expense of sensitivity. The tradeoff between dynamic range and sensitivity can be quantified by the dimensionless ratio between the two numbers. This ratio is interpreted as a degree of difficulty for a measurement. Combined with absolute testing, immersion provides the ability to measure fast cylindrical lenses, which are notoriously difficult to test. Understanding the parameters of the interferometer provides a simple condition for determining the gain from immersion.
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Tan, Zhen. "Electromagnetic metagratings for efficient wavefront manipulation." Electronic Thesis or Diss., Paris 10, 2024. http://www.theses.fr/2024PA100031.
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Par rapport aux métasurfaces traditionnelles, les métaréseaux ont démontré des avantages prononcés dans la manipulation efficace du front d’onde au cours de ces dernières années. Ces avantages découlent principalement de deux facteurs clés : premièrement, les métaréseaux éliminent efficacement la désadaptation d’impédance d’onde entre les ondes entrantes et sortantes, permettant ainsi d’avoir une efficacité quasi-optimale dans la manipulation du front d’onde. Deuxièmement, la structure simplifiée et éparse des métaréseaux les rend beaucoup plus faciles à réaliser que les métasurfaces traditionnelles, qui impliquent souvent des exigences de résolution structurelle complexes, en particulier à des fréquences élevées. Cette thèse s’efforce d’établir une méthodologie de conception plus intuitive et plus rigoureuse pour la manipulation du front d’onde basée sur les métaréseaux, tout en explorant de nouvelles voies dans le domaine. Menée conjointement par l’Université Paris Nanterre et Xi’an Jiaotong University, l’étude commence par une analyse complète des caractéristiques électromagnétiques inhérentes aux métaréseaux, visant à clarifier les principes fondamentaux régissant la manipulation du front d’onde. Cette analyse englobe la dérivation des coefficients de réflexion et de transmission dans les milieux multicouches, l’analyse des caractéristiques du rayonnement et des considérations méticuleuses pour obtenir une manipulation optimale du front d’onde. Les travaux de recherche portent sur les subtilités de la conception des métaréseaux réfléchissants, en abordant les défis et en concevant des stratégies pour les rayonnements mono- et multi-faisceaux et pour l’absorption électromagnétique, en explorant l’influence de diverses configurations structurelles sur la bande passante d’absorption. Notamment, le concept de métaréseaux à impédance de charge nulle est introduit et des applications potentielles sont explorées, en particulier dans les scénarios à hautes fréquences. Enfin, les travaux de recherche étendent leur exploration aux métaréseaux transmissifs, dans le but de démontrer leurs capacités à réaliser diverses manipulations, englobant la réflexion anormale, la réfraction anormale, la division du faisceau, l’absorption d’ondes unidirectionnelle et bidirectionnelle et la manipulation asymétrique du front d’ondeCompared to traditional metasurfaces, metagratings have demonstrated pronounced advantages in efficient wavefront manipulation in recent years. These advantages primarily stem from two key factors: first, metagratings effectively eliminate wave impedance mismatch between incoming and outgoing waves, thus facilitating near-optimal efficiency in wavefront manipulation. Second, the sparsely arranged and simplified structure of metagratings renders them significantly easier to fabricate compared to traditional metasurfaces, which often entail complex structural resolution requirements particularly at high frequencies. This doctoral research endeavors to establish a more intuitive and rigorous design methodology for metagrating-based wavefront manipulation while also exploring novel avenues in the domain. Conducted jointly by Université Paris Nanterre and Xi’an Jiaotong University, the study starts with a comprehensive analysis of the electromagnetic characteristics inherent to metagratings, aiming to elucidate the fundamental principles governing wavefront manipulation. This analysis encompasses the derivation of reflection and transmission coefficients in multilayered media, examination of radiation characteristics, and meticulous considerations for achieving optimal wavefront manipulation. Subsequent investigations deal with the design intricacies of reflective metagratings, addressing challenges and devising strategies for both single-beam and multi-beam radiations and for electromagnetic absorption, exploring the influence of diverse structural configurations on absorption bandwidth. Notably, the concept of zero load-impedance metagratings is introduced and potential applications are explored particularly in high-frequency band scenarios. Finally, the research extends its exploration to transmissive metagratings, aiming to demonstrate their capabilities in achieving diverse wavefront manipulations, encompassing anomalous reflection, anomalous refraction, beam splitting, uni- and bi-directional wave absorption, and asymmetrical wavefront manipulation
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Powell, Keith. "Next generation wavefront controller for the MMT adaptive optics system: Algorithms and techniques for mitigating dynamic wavefront aberrations." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/222838.
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Wavefront controller optimization is important in achieving the best possible image quality for adaptive optics systems on the current generation of large and very large aperture telescopes. This will become even more critical when we consider the demands of the next generation of extremely large telescopes currently under development. These telescopes will be capable of providing resolution which is significantly greater than the current generation of optical/IR telescopes. However, reaching the full resolving potential of these instruments will require a careful analysis of all disturbance sources, then optimizing the wavefront controller to provide the best possible image quality given the desired science goals and system constraints. Along with atmospheric turbulence and sensor noise, structural vibration will play an important part in determining the overall image quality obtained. The next generation of very large aperture telescopes currently being developed will require assessing the effects of structural vibration on closed loop AO system performance as an integral part of the overall system design. Telescope structural vibrations can seriously degrade image quality, resulting in actual spot full width half maximum (FWHM) and angular resolution much worse than the theoretical limit. Strehl ratio can also be significantly degraded by structural vibration as energy is dispersed over a much larger area of the detector. In addition to increasing telescope diameter to obtain higher resolution, there has also been significant interest in adaptive optics systems which observe at shorter wavelength from the near infrared to visible (VNIR) wavelengths, at or near 0.7 microns. This will require significant reduction in the overall wavefront residuals as compared with current systems, and will therefore make assessment and optimization of the wavefront controller even more critical for obtaining good AO system performance in the VNIR regime.
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Moshirfar, Majid, Tirth Shah, David Skanchy, Steven Linn, Paul Kang, and Daniel Durrie. "Comparison and analysis of FDA reported visual outcomes of the three latest platforms for LASIK: wavefront guided Visx iDesign, topography guided WaveLight Allegro Contoura, and topography guided Nidek EC-5000 CATz." DOVE MEDICAL PRESS LTD, 2017. http://hdl.handle.net/10150/622646.
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Purpose: To compare and analyze the differences in visual outcomes between Visx iDesign Advanced WaveScan Studio (TM) System, Alcon Wavelight Allegro Topolyzer and Nidek EC-5000 using Final Fit (TM) Custom Ablation Treatment Software from the submitted summary of safety and effectiveness of the US Food and Drug Administration (FDA) data. Methods: In this retrospective comparative study, 334 eyes from Visx iDesign, 212 eyes from Alcon Contour, and 135 eyes from Nidek CATz platforms were analyzed for primary and secondary visual outcomes. These outcomes were compared via side-by-side graphical and tabular representation of the FDA data. Statistical significance was calculated when appropriate to assess differences. A P-value <0.05 was considered statistically significant. Results: The mean postoperative uncorrected distance visual acuity (UDVA) at 12 months was 20/19.25 +/- 8.76, 20/16.59 +/- 5.94, and 20/19.17 +/- 4.46 for Visx iDesign, Alcon Contoura, and Nidek CATz, respectively. In at least 90% of treated eyes at 3 months and 12 months, all three lasers showed either no change or a gain of corrected distance visual acuity (CDVA). Mesopic contrast sensitivity at 6 months showed a clinically significant increase of 41.3%, 25.1%, and 10.6% for eyes using Visx iDesign, Alcon Contoura, and Nidek CATz, respectively. Photopic contrast sensitivity at 6 months showed a clinically significant increase of 19.2%, 31.9%, and 10.6% for eyes using Visx iDesign, Alcon Contoura, and Nidek CATz, respectively. Conclusion: FDA data for the three platforms shows all three were excellent with respect to efficacy, safety, accuracy, and stability. However, there are some differences between the platforms with certain outcome measurements. Overall, patients using all three lasers showed significant improvements in primary and secondary visual outcomes after LASIK surgery.
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Varslot, Trond. "Wavefront aberration correction in medical ultrasound imaging." Doctoral thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1906.
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Medisinsk ultralydavbildning er et relativt rimelig verktøy som er i utstrakte bruk på dagens sykehus og tildels også legekontor. En underliggende antakelse ved dagens avbildningsteknikker er at vevet som skal avbildes i grove trekk er homogent. Det vil i praksis si at de akustiske egenskapene varierer lite. I tilfeller der denne forutsetningen ikke holder vil resultatet bli betraktlig reduksjon av bildekvaliteten. Prosjektet har fokusert på hvordan man best mulig kan korrigere for denne kvalitetsforringelsen. Arbeidet har resultert i et styrket teoretisk rammeverk for modellering, programvare for numerisk simulering. Rammeverket gir en felles forankring for tidligere publiserte metoder som "time-reversal mirror", "beamsum-correlation" og "speckle brightness", og gir derfor en utvidet forståelse av disse metodene. Videre har en ny metode blitt utviklet basert på egenfunksjonsanalyse av et stokastisk tilbakespredt lydfelt. Denne metoden vil potensielt kunne håndtere sterk spredning fra områder utenfor hovedaksen til ultralydstrålen på en bedre måte enn tidligere metoder. Arbeidet er utført ved Institutt for matematiske fag, NTNU, med professor Harald Krogstad, Institutt for matematiske fag, som hovedveileder og professor Bjørn Angelsen, Institutt for sirkulasjon og bildediagnostikk, som medveileder.
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Roney, Caroline Helen. "Mathematical techniques for assessing cardiac wavefront dynamics." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/39976.
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Electrical signals measured during cardiac arrhythmias may be difficult to analyse and there are multiple challenges associated with their interpretation, including noise, variability between and within datasets, data resolution, and complicated wavefront behaviour. This thesis aimed to develop and test techniques for analysing cardiac electrical wavefront dynamics applied to in vitro, in silico in vivo data. One such technique was developed to determine conduction velocity and to estimate the location of the origin of a focal source, assuming either a planar or circular wavefront, measured from any arbitrary arrangement of recording points. This algorithmic technique performed well on simulated and clinical data, and was extended to incorporate curvature of the atrium. The sensitivity to filtering and post-processing parameters of a technique for tracking rotational sources in optical mapping experiments was investigated, and an optimal parameter set was determined. This was used alongside a technique developed to calculate the distribution of new wavefront initiation sites, in order to gain insight into the mechanisms sustaining atrial fibrillation. The technique for tracking rotational sources was extended to work for unipolar and bipolar electrogram data. This extension was tested in simulation against action potential data, where the modalities (unipolar electrogram, bipolar electrogram and action potential phase) were found to perform similarly; and then applied to experimental and clinical electrograms. Rotational content and activation maps were found to be similar for clinical unipolar and bipolar phase. The developed techniques were used to investigate the effects of spatial resolution on the identification of rotors and focal sources, as a function of the distance between successive wavefronts. A technique was presented to estimate this distance from a small number of measuring points, providing experimental and clinical utility. These requirements were then tested for simulated high-density mapping catheters and basket catheters, where all catheters provided sufficient resolution.
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Oag, Thomas J. D. "Interferometric wavefront sensing for extreme adaptive optics." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3101/.
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Adaptive optics is concerned with the correction of phase distortions in wavefronts which degrade the quality of images produced by optical systems. It was originally developed for both astronomy and the military, where the Earth's atmosphere causes distortions, although other uses are now being developed. As ground based telescopes become increasingly large the size and complexity of adaptive optics systems also increase, creating "extreme adaptive optics”. This thesis deals with such an adaptive optics system. A novel self referenced phase shifting interferometer based on a liquid crystal (LC) waveplate is presented which can measure high spatial frequency phase distortions. This is then coupled to a LC spatial light modulator wavefront corrector. The geometry is matched such that there is no need for a wavefront reconstructor. The performance is measured in two stages. Firstly, spatially where static phase distortions are measured by the interferometer and corrected. Secondly, temporally where a simple analogue feedback is implemented to show correction over a single corrector pixel for fast time varying phase distortions. This work builds on other published research on using point diffraction interferometry in adaptive optics. The novelty lies in the development of a new implementation of a point diffraction interferometer, and in the demonstration of a high-speed closed loop single channel system. This work therefore contributes to the groundwork required to build an extreme adaptive optics system whose complexity scales linearly with the size (area) of the telescope aperture.
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Ash, Darren. "Optimal wavefront sensing for adaptive optics systems." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297368.
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Lu, Jiahui. "Designing wavefront sensors from liquid crystal microlenses." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707989.
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Teich, M., J. Sturm, L. Büttner, and J. Czarske. "Distortion-free 3D imaging using wavefront shaping." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A34966.
Full textAbstract:
3-dimensional imaging often requires substantial effort since information along the optical axis is not straight forward gatherable. In many applications it is aimed for depth information along the direction of view. For example fluidic mixing processes and the environmental interaction on a microscopic scale are of particular importance for e.g. pharmaceutical applications and often demand for 3D information. This problem is often solved by stereoscopic approaches, where two cameras are used in order to gather depth information by triangulation technique. Another approach is to scan the object through the focal plane in order to get sharp images of each layer. Since the before mentioned approaches require a lot of video data to be evaluated it would be more convenient to get depth mapping within a single camera recording and without scanning. Here we present a tunable 3D depth-mapping camera technique in combination with dynamic aberration control. By using an incoherent light source, only one camera and a spatial light modulator (LCoS-SLM), it is a simply applicable and highly scalable technique. A double-helix point spread function (DH-PSF) is generated for light emerging from the bserved focal plane. Each object appears as a double-image on the camera. Within the orientation of the double-image, depth information along the optical axis is encoded. By using an additional adaptive element (deformable mirror) the technique is combined with wide-field aberration correction. Here we combine a tunable 3D depth camera with dynamic aberration control in one imaging system.
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Khandekar, Rahul M. "Advanced wavefront manipulation technologies in optical systems." Diss., Online access via UMI:, 2008.
Find full textAbstract:
Thesis (Ph. D.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Electrical Engineering, 2008.Includes bibliographical references.
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Korablinova, Nina. "Measuring corneal topography using wavefront analysis technique." [S.l. : s.n.], 2004. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-65645.
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Chang, YuChun. "Diffraction wavefront analysis of computer-generated holograms." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284879.
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Computer-generated holograms (CGHs) use diffraction to create wavefronts of light with desired amplitude and phase variations. The amplitude control is well known. But the sensitivity of phase, which is most important for some applications, such as interferometry, is less known. This dissertation studies phase errors resulted from design and fabrication limitations of CGHs. Fabrication uncertainties of CGHs are primarily responsible for the degradation of the quality of wavefronts generated by CGHs. In this dissertation, the binary linear diffraction model is introduced to study wavefront phase errors caused by substrate figure errors, pattern distortion, grating duty-cycle and etching depth errors. Wavefront sensitivity functions derived from diffraction model provide analytical solutions to estimate phase deviations due to duty-cycle or phase depth variations. The results of the wavefront sensitivity analysis also enable us to identify hologram structures that are the most sensitive, as well as the least sensitive to fabrication uncertainties. Experiments were conducted to validate the diffraction model. Example error budgets for common CGH optical testing configurations are demonstrated. In addition, a graphical representation of the diffraction fields is introduced. It provides an intuitive way for diffraction wavefront analysis and explains phase discontinuous observed in the diffraction model. Scalar diffraction models are commonly used in CGH analysis and modeling due to their computational simplicity compared with rigorous diffraction models. The validity of the scalar diffraction models becomes unclear when they are used to analyze diffractive elements with wavelength-scaled features. This dissertation discusses the validity of the scalar diffraction models with giving emphasis to wavefront phase. Fourier modal method (FMM) derived from rigorous diffraction theory is used to study a binary zone plate. The result of this analysis is compared with experimental data, This study shows that polarization sensitivities of the hologram are almost negligible for the chrome-on-glass zone plate with a minimum ring spacing of 2lambda. This result implies that scalar diffraction models may still be sufficient for modeling the phase from holograms with wavelength-scaled diffraction features for the case studied in this dissertation.
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Zhu, Mingxia. "Microfluctuations of Wavefront Aberrations of the Eye." Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/16121/1/Mingxia_Zhu_Thesis.pdf.
Full textAbstract:
The human eye suffers various optical aberrations that degrade the retinal image. These aberrations include defocus and astigmatism, as well as the higher order aberrations that also play an important role in our vision. The optics of the eye are not static, but are continuously fluctuating. The work reported in this thesis has studied the nature of the microfluctuations of the wavefront aberrations of the eye and has investigated factors that influence the microfluctuations.
The fluctuations in the ocular surface of the eye were investigated using high speed videokeratoscopy which measures the dynamics of the ocular surface topography. Ocular surface height difference maps were computed to illustrate the changes in the tear film in the inter-blink interval. The videokeratoscopy data was used to derive the ocular surface wavefront aberrations up to the 4th radial order of the Zernike polynomial expension. We examined the ocular surface dynamics and temporal changes in the ocular surface wavefront aberrations in the inter-blink interval. During the first 0.5 sec following a blink, the tear thickness at the upper edge of the topography map appeared to thicken by about 2 microns. The influence of pulse and instantaneous pulse rate on the microfluctuations in the corneal wavefront aberrations was also investigated. The fluctuations in ocular surface wavefront aberrations were found to be uncorrelated with the pulse and instantaneous heart rates. In the clinical measurement of the ocular surface topography using videokeratoscopy, capturing images 2 to 3 seconds after a blink will result in more consistent results.
To investigate fluctuations in the wavefront aberrations of the eye and their relation to pulse and respiration frequencies we used a wavefront sensor to measure the dynamics of the aberrations up to the Zernike polynomial 4th radial order. Simultaneously, the subject's pulse rate was measured, from which the instantaneous heart rate was derived. An auto-regressive process was used to derive the power spectra of the Zernike aberration signals, as well as pulse and instantaneous heart rate signals. Linear regression analysis was performed between the frequency components of Zernike aberrations and the pulse and instantaneous heart rate frequencies. Cross spectrum density and coherence analyses were also applied to investigate the relation between fluctuations of wavefront aberrations and pulse and instantaneous heart rate. The correlations between fluctuations of individual Zernike aberrations were also determined. A frequency component of all Zernike aberrations up to the 4th radial order was found to be significantly correlated with the pulse frequency (all > 2R0.51, p<0.02), and a frequency component of 9 out of 12 Zernike aberrations was also significantly correlated with instantaneous heart rate frequency (all>2R0.46, p<0.05). The major correlations among Zernike aberrations occurred between second order and fourth order aberrations with the same angular frequencies. Higher order aberrations appear to be related to the cardiopulmonary system in a similar way to that reported for the accommodation signal and pupil fluctuations.
A wavefront sensor and high speed videokeratoscopy were used to investigate the contribution of the ocular surface, the effect of stimulus vergence, and refractive error on the microfluctuations of the wavefront aberrations of the eye. The fluctuations of the Zernike wavefront aberrations were quantified by their variations around the mean and using power spectrum analysis. Integrated power was determined in two regions: 0.1 Hz ─ 0.7 Hz (low frequencies) and 0.8 Hz ─ 1.8 Hz (high frequencies). Changes in the ocular surface topography were measured using high speed videokeratoscopy and variations in the ocular wavefront aberrations were calculated. The microfluctuations of wavefront aberrations in the ocular surface were found to be small compared with the microfluctuations of the wavefront aberrations in the total eye. The variations in defocus while viewing a closer target at 2 D and 4 D stimulus vergence were found to be significantly greater than variations in defocus when viewing a far target. This increase in defocus fluctuations occurred in both the low and high frequency regions (all p<0.001) of the power spectra. The microfluctuations in astigmatism and most of the 3rd order and 4th order Zernike wavefront aberrations of the total eye were found to significantly increase with the magnitude of myopia.
The experiments reported in this thesis have demonstrated the characteristics of the microfluctuations of the wavefront aberrations of the eye and have shown some of the factors that can influence the fluctuations. Major fluctuation frequencies of the eye's wavefront aberrations were shown to be significantly correlated with the pulse and instantaneous heart rate frequencies. Fluctuations in the ocular surface wavefront aberrations made a small contribution to those of the total eye. Changing stimulus vergence primarily affected the fluctuations of defocus in both low and high frequency components. Variations in astigmatism and most 3rd and 4th order aberrations were associated with refractive error magnitude. These findings will aid our fundamental understanding of the complex visual optics of the human eye and may allow the opportunity for better dynamic correction of the aberrations with adaptive optics.
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Zhu, Mingxia. "Microfluctuations of Wavefront Aberrations of the Eye." Queensland University of Technology, 2005. http://eprints.qut.edu.au/16121/.
Full textAbstract:
The human eye suffers various optical aberrations that degrade the retinal image. These aberrations include defocus and astigmatism, as well as the higher order aberrations that also play an important role in our vision. The optics of the eye are not static, but are continuously fluctuating. The work reported in this thesis has studied the nature of the microfluctuations of the wavefront aberrations of the eye and has investigated factors that influence the microfluctuations. The fluctuations in the ocular surface of the eye were investigated using high speed videokeratoscopy which measures the dynamics of the ocular surface topography. Ocular surface height difference maps were computed to illustrate the changes in the tear film in the inter-blink interval. The videokeratoscopy data was used to derive the ocular surface wavefront aberrations up to the 4th radial order of the Zernike polynomial expension. We examined the ocular surface dynamics and temporal changes in the ocular surface wavefront aberrations in the inter-blink interval. During the first 0.5 sec following a blink, the tear thickness at the upper edge of the topography map appeared to thicken by about 2 microns. The influence of pulse and instantaneous pulse rate on the microfluctuations in the corneal wavefront aberrations was also investigated. The fluctuations in ocular surface wavefront aberrations were found to be uncorrelated with the pulse and instantaneous heart rates. In the clinical measurement of the ocular surface topography using videokeratoscopy, capturing images 2 to 3 seconds after a blink will result in more consistent results. To investigate fluctuations in the wavefront aberrations of the eye and their relation to pulse and respiration frequencies we used a wavefront sensor to measure the dynamics of the aberrations up to the Zernike polynomial 4th radial order. Simultaneously, the subject's pulse rate was measured, from which the instantaneous heart rate was derived. An auto-regressive process was used to derive the power spectra of the Zernike aberration signals, as well as pulse and instantaneous heart rate signals. Linear regression analysis was performed between the frequency components of Zernike aberrations and the pulse and instantaneous heart rate frequencies. Cross spectrum density and coherence analyses were also applied to investigate the relation between fluctuations of wavefront aberrations and pulse and instantaneous heart rate. The correlations between fluctuations of individual Zernike aberrations were also determined. A frequency component of all Zernike aberrations up to the 4th radial order was found to be significantly correlated with the pulse frequency (all > 2R0.51, p<0.02), and a frequency component of 9 out of 12 Zernike aberrations was also significantly correlated with instantaneous heart rate frequency (all>2R0.46, p<0.05). The major correlations among Zernike aberrations occurred between second order and fourth order aberrations with the same angular frequencies. Higher order aberrations appear to be related to the cardiopulmonary system in a similar way to that reported for the accommodation signal and pupil fluctuations. A wavefront sensor and high speed videokeratoscopy were used to investigate the contribution of the ocular surface, the effect of stimulus vergence, and refractive error on the microfluctuations of the wavefront aberrations of the eye. The fluctuations of the Zernike wavefront aberrations were quantified by their variations around the mean and using power spectrum analysis. Integrated power was determined in two regions: 0.1 Hz ─ 0.7 Hz (low frequencies) and 0.8 Hz ─ 1.8 Hz (high frequencies). Changes in the ocular surface topography were measured using high speed videokeratoscopy and variations in the ocular wavefront aberrations were calculated. The microfluctuations of wavefront aberrations in the ocular surface were found to be small compared with the microfluctuations of the wavefront aberrations in the total eye. The variations in defocus while viewing a closer target at 2 D and 4 D stimulus vergence were found to be significantly greater than variations in defocus when viewing a far target. This increase in defocus fluctuations occurred in both the low and high frequency regions (all p<0.001) of the power spectra. The microfluctuations in astigmatism and most of the 3rd order and 4th order Zernike wavefront aberrations of the total eye were found to significantly increase with the magnitude of myopia. The experiments reported in this thesis have demonstrated the characteristics of the microfluctuations of the wavefront aberrations of the eye and have shown some of the factors that can influence the fluctuations. Major fluctuation frequencies of the eye's wavefront aberrations were shown to be significantly correlated with the pulse and instantaneous heart rate frequencies. Fluctuations in the ocular surface wavefront aberrations made a small contribution to those of the total eye. Changing stimulus vergence primarily affected the fluctuations of defocus in both low and high frequency components. Variations in astigmatism and most 3rd and 4th order aberrations were associated with refractive error magnitude. These findings will aid our fundamental understanding of the complex visual optics of the human eye and may allow the opportunity for better dynamic correction of the aberrations with adaptive optics.
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BARTOLUCCI, FRANCESCA. "Radon transforms: Unitarization, Inversion and Wavefront sets." Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/997903.
Full textAbstract:
The first contribution of this thesis is a new approach based on the theory of group representations in order to solve in a general an unified way the unitarization and inversion problems for generalized Radon transform associated to dual pairs (G/K,G/H) of homogeneous spaces of a locally compact group G, where K and H are closed subgroups of G. Precisely, under some technical assumptions, if the quasi-regular representations of G acting on L^2(G/K) and L^2(G/H) are irreducible, then the Radon transform, up to a composition with a suitable pseudo-differential operator, can be extended to a unitary operator intertwining the two representations. If, in addition, the representations are square integrable, an inversion formula for the Radon transform based on the voice transform associated to these representations is given. Several examples are discussed. The second purpose of the thesis is to investigate the connection between the shearlet transform and the wavelet transform, which has to be found in the Radon transform in affine coordinates. This link yields a formula for the shearlet transform that involves only integral transforms applied to the affine Radon transform of the signal, thereby opening new perspectives both for finding a new algorithm to compute the shearlet transform of a signal and for the inversion of the Radon transform. Furthermore, we study the role of the Radon transform in microlocal analysis, especially in the resolution of the wavefront set in shearlet analysis. We propose a new approach based on the wavelet transform and on the Radon transform which clarifies how the ability of the shearlet transform to characterize the wavefront set of signals follows directly by the combination of the microlocal properties inhereted by the one-dimensional wavelet transform with a sensitivity for directions inhereted by the Radon transform. Finally, the last chapter of the thesis is devoted to the extension of the shearlet transform to distributions. Our main results are continuity theorems for the shearlet transform and its transpose, called the shearlet synthesis operator, on various test function spaces. Then, we use these continuity results to develop a distributional framework for the shearlet transform via a duality approach. This work arises from the lack in the theory of a complete distributional framework for the shearlet transform and from the link between the shearlet transform with the Radon and the wavelet transforms, whose distribution theory is a deeply investigated and well known subject in applied mathematics.
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Lin, Menglan. "Functionality-multiplexing metasurfaces for electromagnetic wavefront manipulation." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST052.
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Les métasurfaces à multiplexage de fonctionnalités ont attiré une attention considérable en tant que candidats prometteurs pour faire face à l'intégration et à la miniaturisation des dispositifs. De telles métasurfaces permettent d'obtenir différentes fonctionnalités à partir d'un seul dispositif. Pour développer des méta-dispositifs dans le régime des micro-ondes, certains enjeux ne peuvent pas être ignorées. Cette thèse de doctorat est consacrée à l'exploration de différentes méthodologies pour réaliser des méta-dispositifs à multiplexage de fonctionnalités, en se concentrant sur des questions critiques telles que la manipulation indépendante de l'état de spin, la large bande passante de fonctionnement, le contrôle indépendant et la régulation en temps réel. Des validations numériques et expérimentales ont été faites pour plusieurs applications de manipulation d'ondes électromagnétiques dans chaque méta-dispositif. Les travaux ont été réalisés conjointement par l'Université Paris-Saclay et Xidian University. Tout d'abord, un méta-dispositif passif de multiplexage de polarisations est développé pour réaliser une manipulation d'amplitude indépendante et une modulation complète de phase dépendante pour les états de polarisation circulaire orthogonale. Divers générateurs de faisceaux vortex sont ensuite mis en œuvre pour des états de spin orthogonaux dans une large bande de fréquences et une absorption sélective de spin à la fréquence de résonance est ciblée. Un méta-dispositif réorganisable mécaniquement est également réalisé, où une modulation de phase dynamique est obtenue en enfichant des méta-atomes dans une structure entièrement diélectrique. La capacité de ce méta-dispositif pour la manipulation du front d'onde est étudiée au travers de deux fonctionnalités dans une large bande de fréquences, à savoir des générateurs de faisceaux vortex avec des charges topologiques différentes et des hologrammes en champ proche avec des motifs d'imagerie accordables. Enfin, une métasurface reconfigurable électroniquement, constituée de méta-atomes adressables individuellement, est exploitée pour la focalisation en champ proche à différentes distances focales sur la base du mécanisme de superoscillation. De plus, des faisceaux bouteille unidimensionnels et bidimensionnels sont générés avec différents rayons de trajectoires circulairesFunctionality-multiplexing metasurfaces have attracted considerable attention as prominent candidates for coping with device integration and miniaturization. Such metasurfaces enable different functionalities to be achieved from a single device. To develop meta-devices in the microwave regime, some issues cannot be ignored. This PhD thesis is devoted to exploring different methodologies to realize functionality-multiplexing meta-devices, focusing on critical issues such as independent spin-state manipulation, wide operating bandwidth, independent controllability and real-time regulation. Numerical and experimental validation have been conducted for several applications of electromagnetic wave manipulation in each functionality-multiplexing meta-device. The work was done jointly by Université Paris-Saclay and Xidian University. First, a polarization-multiplexing passive meta-device is developed to achieve independent amplitude manipulation and dependent full-phase modulation for orthogonal circularly polarized states. Diverse vortex beam generators are then implemented for orthogonal spin-states in a wide frequency band and a spin-selective absorption at the resonance frequency is targeted. A mechanically re-organizable meta-device is also realized, where a dynamic phase modulation is achieved by plugging meta-atoms in an all-dielectric structure. The capability of this meta-device for wavefront manipulation is investigated through two functionalities in a wide frequency band, i.e., vortex beam generators with different topological charges and near-field holograms with tunable imaging patterns. Finally, an electronically reconfigurable metasurface, consisting of individually addressable meta-atom, is exploited for near-field focusing at different focal lengths based on the superoscillation mechanism. Additionally, one-dimensional and two-dimensional bottle beams are generated with different radii of circular trajectories
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Costa, Joana Büchler. "Development of a new infrared pyramid wavefront sensor." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974121045.
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Ricciardi, Sébastien. "Polymeric Microcavities for Dye Lasers and Wavefront Shapers." Licentiate thesis, KTH, Microelectronics and Applied Physics, MAP, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4655.
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Over the last few years, the available computing power allows us to have a deeper insight into photonics components than we ever had before. In this thesis we use the finite element method (FEM) to explore the behavior of the waves in 2D planar microcavities. We demonstrate the tunability of the cavity over a wide range of frequencies taking into account both the thermo-mechanical and the thermo-optical effect. Geometry and material choices are done so that the latter is predominant. We also demonstrate an odd mode disappearing phenomenon reported here for the first time as far as we know. Using this knowledge, we design two structures with these remarkable properties.
One of the devices will be used as micro-sized solid-state dye laser with Rhodamine 6G as the active medium and SU-8 polymer as a cavity material in sizes that have never been reached before. This opens new opportunities not only for future implementation for “labs-on-a-chip” (LOC) but also for a higher integration density of optical communication systems. The second device is a wavefront shaper creating plane waves from a point source performing the functions of beam shaper and beam splitter with plane wave as the output result.
After an introduction to FEM and comparison with a rival algorithm, some issues related to FEM in electromagnetic simulation are resolved and explained. Finally, some fabrication techniques with feature sizes <100 nm, such as electron beam lithography (EBL) and nano-imprint lithography (NIL), are described and compared with other lithographic techniques.
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Clare, Richard M. "Wavefront sensing and phase retrieval for astronomical imaging." Thesis, University of Canterbury. Electrical and Computer Engineering, 2004. http://hdl.handle.net/10092/7841.
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Images of astronomical objects captured by ground-based telescopes are distorted by the earth's atmosphere. The atmosphere consists of random time-varying layers of air of differing density and hence refractive index. These refractive index fluctuations cause wavefronts that propagate through the atmosphere to become aberrated, resulting in a loss in resolution of the astronomical images.
The wavefront aberrations that are induced by the atmosphere can be compensated by either real-time adaptive optics, where a deformable mirror is placed in the optical path, or by computer post-processing algorithms on the distorted images. In an adaptive optics system, the wavefront sensor is the element that estimates the wavefront phase aberration. The wavefront cannot be measured directly, and instead an aberration is introduced to the optical path to produce two or more intensity distributions, from which the wavefront slope or curvature can be estimated. Wavefront sensing is one of the topics of this thesis. A number of computer post-processing algorithms exist to deblur astronomical images, such as phase diversity, deconvolution from wavefront sensing (DWFS) and phase retrieval, with improvements to the latter two published in this thesis.
The pyramid wavefront sensor consists of a four-sided glass prism placed in the focal plane of the telescope, which subdivides the focal plane in four, and a relay lens which re-images the four sections of the focal plane to form four images of the aperture at the conjugate aperture plane. The wavefront slope is estimated as a linear combination of the aperture images. The pyramid sensor can be generalised to a class of N-sided glass prism wavefront sensors that subdivide the focal plane into N equal sections, forming N aperture images at the conjugate aperture plane. The minimum number of sides required to estimate the slope in two orthogonal directions is three, and the cone sensor is derived by letting N tend to infinity. Simulation results show that in the presence of photon, but not read, noise the cone sensor provides the best wavefront estimate.
For the pyramid sensor, the wavefront is typically reconstructed from the estimate of the wavefront slope in two orthogonal directions. Some information is inherently lost when the four measurements (aperture images) are reduced to two slope estimates. A new method is proposed to reconstruct the wavefront directly from the aperture images, removing the intermediate step of forming the slope estimates. Reconstructing the wavefront directly from the images is shown through simulation of atmospheric phase screens to give a better wavefront estimate than reconstructing from the slope estimates. This result is true for all pyramid type sensors tested.
The pyramid wavefront sensor can be generalised by placing the lenslet array at the focal plane to subdivide the complex field in the focal plane into more than four sections. Using this framework, the pyramid sensor can be considered as the dual of the Shack Hartmann sensor, which subdivides the aperture plane with a lenslet array, since the two sensors subdivide each one of a Fourier pair. Both sensors estimate the wavefront slope with a centroid operator on the low resolution images. Also, in both sensors there exists a trade-off between the spatial resolution obtainable and the accuracy of the slope estimates. This trade-off is determined by the size of the lenslets in the array for both sensors, and is inverted between the two sensors. Simulation results run in open loop demonstrate that the lenslet array at the aperture (Shack-Hartmann) and focal (pyramid) planes do provide wavefront estimates of equivalent quality. The lenslet array at the focal plane, however, can be modulated so as to increase its linear range and thus provide a better wavefront estimate than the Shack-Hartmann sensor in open loop simulations.
Phase retrieval is a non-linear iterative technique that is used to recover the phase in the aperture plane from intensity measurements at the focal plane and other constraints. A novel phase retrieval algorithm, which subdivides the focal plane of the telescope with a lenslet array and uses the aperture images formed at the conjugate aperture plane as a magnitude constraint, is proposed. This algorithm is more heavily constrained than conventional phase retrieval or phase retrieval in conjunction with the Shack-Hartmann sensor, with constraints applied at three Fourier planes: the aperture, focal and conjugate aperture planes. The subdivision of the focal plane means that the ambiguity problem that exists in other phase retrieval algorithms between an object
A(x,y) and its twin A* (x,y) is removed, and this is supported by simulation results. Simulation results also show that the performance of the algorithm is dependent on the starting point, and that starting with the linear estimate from the aperture images gives a better wavefront estimate than starting with zero phase.
DWFS is a computer post-processing algorithm that combines the distorted image and
wavefront sensing measurements in order to compensate the image for the atmospheric
turbulence. An accurate calibration of the reference positions for the centroids of the Shack-Hartmann sensor is essential for an accurate estimate of the wavefront and hence astronomical object, with DWFS. The conventional method for estimating these reference positions is to image a laser beam through the Shack-Hartmann lenslet array but not through the atmosphere. An alternative calibration technique is to observe a single bright star and optimise the Strehl ratio with respect to the reference positions. Results using DWFS on data captured at the Observatoire de Lyon show that this new technique can provide wavefront estimates of similar quality as the grid calibration technique, but without the need for a separate calibration laser.
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Zou, Weiyao. "OPTIMIZATION OF ZONAL WAVEFRONT ESTIMATION AND CURVATURE MEASUREMENTS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4134.
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Optical testing in adverse environments, ophthalmology and applications where characterization by curvature is leveraged all have a common goal: accurately estimate wavefront shape. This dissertation investigates wavefront sensing techniques as applied to optical testing based on gradient and curvature measurements. Wavefront sensing involves the ability to accurately estimate shape over any aperture geometry, which requires establishing a sampling grid and estimation scheme, quantifying estimation errors caused by measurement noise propagation, and designing an instrument with sufficient accuracy and sensitivity for the application. Starting with gradient-based wavefront sensing, a zonal least-squares wavefront estimation algorithm for any irregular pupil shape and size is presented, for which the normal matrix equation sets share a pre-defined matrix. A Gerchberg–Saxton iterative method is employed to reduce the deviation errors in the estimated wavefront caused by the pre-defined matrix across discontinuous boundary. The results show that the RMS deviation error of the estimated wavefront from the original wavefront can be less than λ/130~ λ/150 (for λ equals 632.8nm) after about twelve iterations and less than λ/100 after as few as four iterations. The presented approach to handling irregular pupil shapes applies equally well to wavefront estimation from curvature data. A defining characteristic for a wavefront estimation algorithm is its error propagation behavior. The error propagation coefficient can be formulated as a function of the eigenvalues of the wavefront estimation-related matrices, and such functions are established for each of the basic estimation geometries (i.e. Fried, Hudgin and Southwell) with a serial numbering scheme, where a square sampling grid array is sequentially indexed row by row. The results show that with the wavefront piston-value fixed, the odd-number grid sizes yield lower error propagation than the even-number grid sizes for all geometries. The Fried geometry either allows sub-sized wavefront estimations within the testing domain or yields a two-rank deficient estimation matrix over the full aperture; but the latter usually suffers from high error propagation and the waffle mode problem. Hudgin geometry offers an error propagator between those of the Southwell and the Fried geometries. For both wavefront gradient-based and wavefront difference-based estimations, the Southwell geometry is shown to offer the lowest error propagation with the minimum-norm least-squares solution. Noll's theoretical result, which was extensively used as a reference in the previous literature for error propagation estimate, corresponds to the Southwell geometry with an odd-number grid size. For curvature-based wavefront sensing, a concept for a differential Shack-Hartmann (DSH) curvature sensor is proposed. This curvature sensor is derived from the basic Shack-Hartmann sensor with the collimated beam split into three output channels, along each of which a lenslet array is located. Three Hartmann grid arrays are generated by three lenslet arrays. Two of the lenslets shear in two perpendicular directions relative to the third one. By quantitatively comparing the Shack-Hartmann grid coordinates of the three channels, the differentials of the wavefront slope at each Shack-Hartmann grid point can be obtained, so the Laplacian curvatures and twist terms will be available. The acquisition of the twist terms using a Hartmann-based sensor allows us to uniquely determine the principal curvatures and directions more accurately than prior methods. Measurement of local curvatures as opposed to slopes is unique because curvature is intrinsic to the wavefront under test, and it is an absolute as opposed to a relative measurement. A zonal least-squares-based wavefront estimation algorithm was developed to estimate the wavefront shape from the Laplacian curvature data, and validated. An implementation of the DSH curvature sensor is proposed and an experimental system for this implementation was initiated. The DSH curvature sensor shares the important features of both the Shack-Hartmann slope sensor and Roddier's curvature sensor. It is a two-dimensional parallel curvature sensor. Because it is a curvature sensor, it provides absolute measurements which are thus insensitive to vibrations, tip/tilts, and whole body movements. Because it is a two-dimensional sensor, it does not suffer from other sources of errors, such as scanning noise. Combined with sufficient sampling and a zonal wavefront estimation algorithm, both low and mid frequencies of the wavefront may be recovered. Notice that the DSH curvature sensor operates at the pupil of the system under test, therefore the difficulty associated with operation close to the caustic zone is avoided. Finally, the DSH-curvature-sensor-based wavefront estimation does not suffer from the 2-ambiguity problem, so potentially both small and large aberrations may be measured.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Torti, Cristiano. "Curvature-based wavefront sensors for the human eye." Thesis, City University London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446340.
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Gelman, Geoffrey M. (Geoffrey Michael) 1977. "Distance estimation through wavefront curvature in cellular systems." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80537.
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Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 78-79).
by Geoffrey M. Gelman.
S.B.and M.Eng.
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Frigerio, Federico Ph D. Massachusetts Institute of Technology. "3-dimensional surface imaging using Active Wavefront Sampling." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38258.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 129-130).
A novel 3D surface imaging technique using Active Wavefront Sampling (AWS) is presented. In this technique, the optical wavefront traversing a lens is sampled at two or more off-axis locations and the resulting motion of each target feature is measured. This target feature image motion can be used to calculate the feature's distance to the camera. One advantage of this approach over traditional stereo techniques is that only one optical train and one sensor can be used to obtain depth information, thereby reducing the bulk and the potential cost of the equipment. AWS based systems are also flexible operationally in that the number of sampling positions can be increased or decreased to respectively raise the accuracy or to raise the processing speed of the system. Potential applications include general machine vision tasks, 3D endoscopy, and microscopy. The fundamental depth sensitivity of an AWS based system will be discussed, and practical implementations of the approach will be described. Algorithms developed to track target features in the images captured at different aperture sampling positions will be discussed, and a method for calibrating an AWS based method will also be described.
by Federico Frigerio.
Ph.D.
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Brooks, Keira J., Laure Catala, Matthew A. Kenworthy, Steven M. Crawford, and Johanan L. Codona. "Polarization dOTF: on-sky focal plane wavefront sensing." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622419.
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The differential Optical Transfer Function (dOTF) is a focal plane wavefront sensing method that uses a diversity in the pupil plane to generate two different focal plane images. The difference of their Fourier transforms recovers the complex amplitude of the pupil down to the spatial scale of the diversity. We produce two simultaneous PSF images with diversity using a polarizing filter at the edge of the telescope pupil, and a polarization camera to simultaneously record the two images. Here we present the first on-sky demonstration of polarization dOTF at the 1.0m South African Astronomical Observatory telescope in Sutherland, and our attempt to validate it with simultaneous Shack-Hartmann wavefront sensor images.
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Sala, Simone. "Wavefront and nanostructure characterisation with X-ray ptychography." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10057099/.
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X-ray ptychography is a scanning diffraction microscopy technique suited for the phase-sensitive investigation of wavefronts and specimens. It returns complex-valued wave functions and transmission functions producing high-resolution (nanoscale) phase- contrast images. This work focuses on the implementation and application of X-ray ptychography in the context of synchrotron radiation facilities. It presents an experimental protocol developed for multiscale X-ray imaging and tested at the I13-1 Coherence Branchline at Diamond Light Source. This protocol combines both near-field and far-field ptychography with other imaging methods, providing a flexible way of conducting experiments on hierarchical structures at any high-brilliance X-ray facility. This work also reports ptychography experiments performed at free-electron lasers, aimed at characterising their pulsed beam. Both the average and individual wavefronts are retrieved through a novel application of a reconstruction algorithm based on singular- value decomposition, giving direct insight on pulse-to-pulse fluctuations and confirming ptychography as a powerful beam diagnostics technique. Additional ptychography experiments are also discussed, which were carried out at storage rings on flat, weakly-scattering biogenic samples to characterise their 3D nanos- tructures. Their data analysis pipeline is presented in detail, from data acquisition to rendered volumes. Furthermore, one of these last experiments constitutes the first successful 3D ptychography experiment run on real-life samples at the I13-1 Coherence Branchline at Diamond Light Source.
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Xue, Jing. "Wavefront Healing and Tomographic Resolution of Mantle Plumes." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50423.
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To investigate seismic resolution of deep mantle plumes as well as the robustness of the anti-correlation between bulk sound speed and S wave speed imaged in the lowermost mantle, we use a Spectral Element Method (SEM) to simulate global seismic wave propagation in 3-D wavespeed models and measure frequency-dependent P-, S-, Pdiff- and Sdiff-wave traveltime anomalies caused by plume structures in the lowermost mantle. We compare SEM time delay measurements with calculations based on ray theory and show that an anti-correlation between bulk sound speed and S-wave speed could be produced as an artifact. This is caused by different wavefront healing effects between P waves and S waves in thermal plume models. The bulk sound speed structure remains poorly resolved when P-wave and S-wave measurements are at different periods with similar wavelength. The differences in wave diffraction between the two types of waves depend on epicentral distance and wave frequency. The artifact in anti-correlation is also confirmed in tomographic inversions based on ray theory using Pdiff and Sdiff time delay measurements made on the SEM synthetics. This indicates a chemical origin of "superplumes" in the lowermost mantle may not be necessary to explain observed seismic traveltimes. The same set of Pdiff and Sdiff measurements are inverted using finite-frequency tomography based on Born sensitivity kernels. We show that wavefront healing effects can be accounted for in finite-frequency tomography to recover the true velocity model.Master of Science
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Glazar, Nikolaus. "Micropatterned Photoalignment for Wavefront Controlled Switchable Optical Devices." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1460650961.
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Murthy, Vinay. "Recovery from transient faults in wavefront processor arrays." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06302009-040356/.
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Cai, Wenrui. "Wavefront Analysis and Calibration for Computer Generated Holograms." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311214.
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Interferometry with computer generated holograms (CGH) has evolved to be a standard technology for optical testing and metrology. By controlling the phase of the diffracted light, CGHs are capable of generating reference wavefronts of any desired shape, which allows using of interferometers for measuring complex aspheric surfaces. Fabrication errors in CGHs, however, cause phase errors in the diffracted wavefront, which directly affects the accuracy and validity of the interferometric measurements. Therefore, CGH fabrication errors must be either calibrated or budgeted. This dissertation is a continuation and expansion of the analysis and calibration of the wavefront errors caused by CGH in optical testing. I will focus on two types of error: encoding error and etching variation induced errors. In Topic one, the analysis of wavefront error introduced by encoding the CGH is discussed. The fabrication of CGH by e-beam or laser writing machine specifically requires using polygon segments to approximate the continuously smooth fringe pattern of an ideal CGH. Wavefront phase errors introduced in this process depend on the size of the polygon segments and the shape of the fringes. We propose a method for estimating the wavefront error and its spatial frequency, allowing optimization of the polygon sizes for required measurement accuracy. This method is validated with both computer simulation and direct measurements from an interferometer. In Topics two, we present a new device, the Diffractive Optics Calibrator (DOC), for measuring etching parameters, such as duty-cycle and etching depth, for CGH. The system scans the CGH with a collimated laser beam, and collects the far field diffraction pattern with a CCD array. The relative intensities of the various orders of diffraction are used to fit the phase shift from etching and the duty cycle of the binary pattern. The system is capable of measuring variations that cause 1 nm peak-to-valley (P-V) phase errors. The device will be used primarily for quality control of the CGHs. DOC is also capable of generating an induced phase error map for calibration. Such calibration is essential for measuring freeform aspheric surfaces with 1 nm root-mean-square (RMS) accuracy.
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Lombini, Matteo <1977>. "Laser guide stars wavefront sensors for the EELT." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3706/1/Lombini_Matteo_tesi.pdf.
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The Adaptive Optics is the measurement and correction in real time of the wavefront aberration of the star light caused by the atmospheric turbulence, that limits the angular resolution of ground based telescopes and thus their capabilities to deep explore faint and crowded astronomical objects. The lack of natural stars enough bright to be used as reference sources for the Adaptive Optics, over a relevant fraction of the sky, led to the introduction of artificial reference stars. The so-called Laser Guide Stars are produced by exciting the Sodium atoms in a layer laying at 90km of altitude, by a powerful laser beam projected toward the sky. The possibility to turn on a reference star close to the scientific targets of interest has the drawback in an increased difficulty in the wavefront measuring, mainly due to the time instability of the Sodium layer density. These issues are increased with the telescope diameter. In view of the construction of the 42m diameter European Extremely Large Telescope a detailed investigation of the achievable performances of Adaptive Optics becomes mandatory to exploit its unique angular resolution .
The goal of this Thesis was to present a complete description of a laboratory Prototype development simulating a Shack-Hartmann wavefront sensor using Laser Guide Stars as references, in the expected conditions for a 42m telescope. From the conceptual design, through the opto-mechanical design, to the Assembly, Integration and Test, all the phases of the Prototype construction are explained. The tests carried out shown the reliability of the images produced by the Prototype that agreed with the numerical simulations. For this reason some possible upgrades regarding the opto-mechanical design are presented, to extend the system functionalities and let the Prototype become a more complete test bench to simulate the performances and drive the future Adaptive Optics modules design.
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Lombini, Matteo <1977>. "Laser guide stars wavefront sensors for the EELT." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3706/.
Full textAbstract:
The Adaptive Optics is the measurement and correction in real time of the wavefront aberration of the star light caused by the atmospheric turbulence, that limits the angular resolution of ground based telescopes and thus their capabilities to deep explore faint and crowded astronomical objects. The lack of natural stars enough bright to be used as reference sources for the Adaptive Optics, over a relevant fraction of the sky, led to the introduction of artificial reference stars. The so-called Laser Guide Stars are produced by exciting the Sodium atoms in a layer laying at 90km of altitude, by a powerful laser beam projected toward the sky. The possibility to turn on a reference star close to the scientific targets of interest has the drawback in an increased difficulty in the wavefront measuring, mainly due to the time instability of the Sodium layer density. These issues are increased with the telescope diameter. In view of the construction of the 42m diameter European Extremely Large Telescope a detailed investigation of the achievable performances of Adaptive Optics becomes mandatory to exploit its unique angular resolution .
The goal of this Thesis was to present a complete description of a laboratory Prototype development simulating a Shack-Hartmann wavefront sensor using Laser Guide Stars as references, in the expected conditions for a 42m telescope. From the conceptual design, through the opto-mechanical design, to the Assembly, Integration and Test, all the phases of the Prototype construction are explained. The tests carried out shown the reliability of the images produced by the Prototype that agreed with the numerical simulations. For this reason some possible upgrades regarding the opto-mechanical design are presented, to extend the system functionalities and let the Prototype become a more complete test bench to simulate the performances and drive the future Adaptive Optics modules design.
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Patti, Mauro <1989>. "MAORY: wavefront sensor prototype and instrument optical design." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8534/1/Mauro_Patti.pdf.
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MAORY will be the multi-conjugate adaptive optics module for the ELT first light. Its main goal is to feed the high-resolution NIR imager and spectrograph MICADO.
The present Thesis address the MAORY system at the level of optical design and analysis.
MAORY is a complex science projects whose stakeholder is the scientific community. Its requirements are driven by the science cases which request high resolution and astrometric accuracy.
In an ideal world without atmospheric turbulence, MAORY optics must deliver diffraction-limited images with very low optical distortions.
The tolerance process is one of the most important step in the instrument design since it is intended to ensure that MAORY requested performances are satisfied when the final assembled instrument is operative.
The baseline is to operate wavefront sensing using six sodium Laser Guide Stars and three Natural Guide Stars to solve intrinsic limitations of artificial sources and to mitigate the impact of the sodium layer structure and variability.
The implementation of a laboratory Prototype for Laser Guide Star wavefront sensor at the beginning of the phase study of MAORY has been indispensable to consolidate the choice of the baseline of wavefront sensing technique.
The first part of this Thesis describes the results obtained with the Prototype for Laser Guide Star wavefront sensor under different working conditions.
The second part describes the logic behind the tolerance analysis at the level of MAORY optical design starting from definition of quantitative figures of merit for requirements and ending with estimation of MAORY performances perturbed by opto-mechanical tolerances.
The sensitivity analysis on opto-mechanical tolerance of MAORY is also a crucial step to plan the alignment concept that concludes the arguments addressed by this Thesis.
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Olivier, Nicolas. "Contrast Mechanisms & Wavefront Control in Coherent Nonlinear Microscopy." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00006255.
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McGaughey, Donald. "Spectral modelling and simulation of atmospherically distorted wavefront data." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ54425.pdf.
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Allen, Matthew R. "Wavefront control for space telescope applications using adaptive optics." Thesis, Monterey, Calif. : Naval Postgraduate School, 2007. http://bosun.nps.edu/uhtbin/hyperion-image.exe/07Dec%5FAllen%5FM.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2007.Thesis Advisor(s): Agrawal, Brij. "December 2007." Description based on title screen as viewed on January 16, 2008. Includes bibliographical references (p. 89-90). Also available in print.
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Brooks, Jonathan Mark. "A compact Shack-Hartmann wavefront sensor for the eye." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416449.
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He, Qubao. "Coherent power combining on spacecraft via wavefront Multiplexing techniques." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527380.
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A novel orthogonal wavefront (WF) Multiplexing (Muxing) and De-Multiplexing (Demuxing) scheme is proposed for uplink from antenna array elements to multiple spacecraft (S/C). By using an adaptive equalization at the receiver of S/C, the phase deviation due to different near field distances of the uplink from antenna array elements to S/C is compensated via the WF Demuxing method on S/C. This scheme allows power combining from antenna array elements to S/C. Besides, this scheme can be extended and applied to multiple S/C. Simulations verify that the proposed scheme achieves the same bit error rate (BER) performance as the theoretical BER in additive white Gaussian noise (AWGN) channels and one path flat fading channel. Furthermore, although the radiated signals among the multiple radiating antenna array elements are non-coherent, the coherent power combining of the radiations of multiple radiating antenna array elements is accomplished on the S/C receiver in the proposed techniques.