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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Tomographic wave-front sensing with a single guide star

Hart, Michael, Jefferies, Stuart, Hope, Douglas 01 November 2016 (has links)
Adaptive optics or numerical restoration algorithms that restore high resolution imaging through atmospheric turbulence are subject to isoplanatic wave-front errors. Mitigating those errors requires that the wave-front aberrations be estimated within the 3D volume of the atmosphere. Present techniques rely on multiple beacons, either natural stars or laser guide stars, to probe the atmospheric aberration along different lines of sight, followed by tomographic projection of the measurements onto layers at defined ranges. In this paper we show that a three-dimensional estimate of the wave-front aberration can be recovered from measurements by a single guide star in the case where the aberration is stratified, provided that the telescope tracks across the sky with non-uniform angular velocity. This is generally the case for observations of artificial earth-orbiting satellites, and the new method is likely to find application in ground based telescopes used for space situational awareness.
2

High Dynamic Range Calibration for an Infrared Shack-Hartmann Wavefront Sensor

Smith, Daniel Gene January 2008 (has links)
Since its invention in the early seventies, the Shack-Hartmann wavefront sensor has seen a wide variety of applications and has had great success in the fields of Adaptive Optics and Ophthalmology, where interferometry is usually impractical. Its application to optical shop testing has been less visible perhaps because shop environments can be manipulated to sufficiently remove vibration and turbulence to a degree that can support interferometry. However, with the growing need to accurately test aspheric optics, the Shack-Hartmann has an advantage; its dynamic range can be manipulated through the design of the lenslet array, rather than being directly tied to the wavelength of light and therefore lessen the need for expensive null optics.When the Shack-Hartmann is pushed to the limits of dynamic range, several issues must be dealt with. First, to reach the limits of dynamic range, those limits must be well understood. This dissertation presents a graphical approach to designing the Shack-Hartmann sensor that makes the trade-off between sensitivity and dynamic range, and accuracy and resolution intuitively clear. Next, the spots that once landed neatly in the region behind each lenslet, may now wander several lenslets away and the data reduction must be able handle this. This dissertation presents a novel and robust method for sorting these widely wondering spots and is shown to work in measurements of highly aspheric elements. Finally, in the high dynamic range regime, induced aberrations can severely limit the accuracy of the instrument. In this dissertation, these non-linear and measurement-dependent errors are studied in detail and a method of compensation is presented along with experimental results that illustrate the efficacy of the approach.
3

The Continuous Wavelet Transform and the Wave Front Set

Navarro, Jaime 12 1900 (has links)
In this paper I formulate an explicit wavelet transform that, applied to any distribution in S^1(R^2), yields a function on phase space whose high-frequency singularities coincide precisely with the wave front set of the distribution. This characterizes the wave front set of a distribution in terms of the singularities of its wavelet transform with respect to a suitably chosen basic wavelet.
4

Daylight operation of a sodium laser guide star for adaptive optics wavefront sensing

Hart, Michael, Jefferies, Stuart M., Murphy, Neil 26 October 2016 (has links)
We report contrast measurements of a sodium resonance guide star against the daylight sky when observed through a tuned magneto-optical filter (MOF). The guide star was created by projection of a laser beam at 589.16 nm into the mesospheric sodium layer and the observations were made with a collocated 1.5-m telescope. While MOFs are used with sodium light detecting and ranging systems during the day to improve the signalto- noise ratio of the measurements, they have not so far been employed with laser guide stars to drive adaptive optics (AO) systems to correct atmospherically induced image blur. We interpret our results in terms of the performance of AO systems for astronomy, with particular emphasis on thermal infrared observations at the next generation of extremely large telescopes now being built. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
5

Design and analysis of a phase mask for mutifocusing

Guo, Jian-You 07 September 2011 (has links)
The image quality will degrade if the misfocusing problem occurs in the imaging system. This paper is aimed to design and analyze a phase mask for mutifocusing problem. Depth of field is the range to get a clear image. As the lens can only gather the light in a fixed range. Image will be more blurred when it is more from this range. In 1995 Dowski and Cathey proposed the wave-front coding to increase the system's depth of field so that the image will less susceptible to blur due to the mutifocusing problem. A treatment with a mask before the lens can extend the depth of field. In this paper, we extend to multi-levels phase mask. The simulation results show that multi-level phase mask has a better performance than the two-level phase mask.
6

Design and analysis of a phase mask to improve the misfocus blur

Chuang, Bo-Jin 13 September 2012 (has links)
In optical imaging system, misfocus occurs because of a nonaccuate focal length. In recent years, the improvement for misfocus problem has caught much attention in researches. This thesis is aimed to explore the misfocus improvement and analysis. Lens plays an important role in optical image system. It can focus light at one point. The distance between the focal point and the lens is called focal length. Focal length is determined by the object distance and the image distance. As light is focused farther out of the focal point, the image will blur. It is called misfocus. The general method to improve misfocus image is done by post-processing. In 1995, wave-front coding was first proposed by Dowski and Cathey. They placed the phase mask in front of the lens, and then emphasized on the processing. In recent years, more and more researches work on this field. In this thesis, a one ring phase mask is designed by modulating the phase difference in the ring to make the improvement better. Research before wave-front coding in order to achieve a closed optical transfer function for different degrees of misfocus, but we hope the phase mask can provide immediate improvement. This idea can be applied to real-time video monitoring.
7

Ray Based Finite Difference Method For Time Domain Electromagnetics

Ciydem, Mehmet 01 September 2005 (has links) (PDF)
In this study, novel Ray Based finite difference method for Time Domain electromagnetics(RBTD) has been developed. Instead of solving Maxwell&rsquo / s hyperbolic partial differential equations directly, Geometrical Optics tools (wavefronts, rays) and Taylor series have been utilized. Discontinuities of electromagnetic fields lie on wavefronts and propagate along rays. They are transported in the computational domain by transport equations which are ordinary differential equations. Then time dependent field solutions at a point are constructed by using Taylor series expansion in time whose coefficients are these transported distincontinuties. RBTD utilizes grid structure conforming to wave fronts and rays and treats all electromagnetic problems, regardless of their dimensions, as one dimensional problem along the rays. Hence CFL stability condition is implemented always at one dimensional eqaulity case on the ray. Accuracy of RBTD depends on the accuracy of grid generation and numerical solution of transport equations. Simulations for isotropic medium (homogeneous/inhomogeneous) have been conducted. Basic electromagnetic phenomena such as propagation, reflection and refraction have been implemented. Simulation results prove that RBTD eliminates numerical dispersion inherent to FDTD and is promising to be a novel method for computational electromagnetics.
8

Geometria Diferencial do conjunto focal / Differential Geometry of the Focal Set

Santos, Samuel Paulino dos 08 February 2018 (has links)
Submitted by Samuel Paulino dos Santos null (samuelp.santos@hotmail.com) on 2018-02-20T18:11:03Z No. of bitstreams: 1 Samuel Dissertacao.pdf: 1684097 bytes, checksum: f23b4c4291af5720876a40f4fad8bc75 (MD5) / Rejected by Elza Mitiko Sato null (elzasato@ibilce.unesp.br), reason: Solicitamos que realize correções na submissão seguindo as orientações abaixo: Problema 01) O arquivo contém 07(sete) páginas em branco, as mesmas devem retiradas. Problema 02) Na Folha de rosto deve constar a financiadora. Ex.: Financiadora: FAPESP – Proc. Problema 03) Na capa e folha de rosto devem constar somente o ano Problema 04) A ficha catalográfica deve ser refeita pois na contagem entraram as páginas em branco.. Na página da Seção de pós-graduação, em Instruções para Qualificação e Defesas de Dissertação e Tese, você pode acessar o modelo das páginas pré-textuais. Lembramos que o arquivo depositado no repositório deve ser igual ao impresso. Agradecemos a compreensão. on 2018-02-21T19:46:00Z (GMT) / Submitted by Samuel Paulino dos Santos null (samuelp.santos@hotmail.com) on 2018-02-22T17:32:54Z No. of bitstreams: 1 Samuel Dissertacao.pdf: 1684097 bytes, checksum: f23b4c4291af5720876a40f4fad8bc75 (MD5) / Rejected by Elza Mitiko Sato null (elzasato@ibilce.unesp.br), reason: Solicitamos que realize correções na submissão seguindo as orientações abaixo: Problema 01) O arquivo contém 07(sete) páginas em branco, as mesmas devem retiradas, pois não pode haver páginas em branco no arquivo. Problema 02) Na Folha de rosto deve constar a financiadora. Ex.: Financiadora: FAPESP – Proc. Problema 03) Na capa e folha de rosto devem constar somente o ano Problema 04) A ficha catalográfica deve ser refeita pois na contagem entraram as páginas em branco. Estamos encaminhando via e-mail o modelo das páginas pré-textuais para que você possa fazer as correções. Lembramos que o arquivo depositado no repositório deve ser igual ao impresso. Agradecemos a compreensão. on 2018-02-22T18:21:23Z (GMT) / Submitted by Samuel Paulino dos Santos null (samuelp.santos@hotmail.com) on 2018-02-22T19:27:58Z No. of bitstreams: 1 Dissertacao-Samuel-CORRECOES.pdf: 1777749 bytes, checksum: 414449c29a5a2c7be6d6e5dc4eb7fbe0 (MD5) / Submitted by Samuel Paulino dos Santos null (samuelp.santos@hotmail.com) on 2018-02-22T19:46:16Z No. of bitstreams: 1 Dissertacao-Samuel-CORRECOES.pdf: 1777749 bytes, checksum: 414449c29a5a2c7be6d6e5dc4eb7fbe0 (MD5) / Approved for entry into archive by Elza Mitiko Sato null (elzasato@ibilce.unesp.br) on 2018-02-23T18:32:09Z (GMT) No. of bitstreams: 1 santos_sp_me_sjrp.pdf: 1777749 bytes, checksum: 414449c29a5a2c7be6d6e5dc4eb7fbe0 (MD5) / Made available in DSpace on 2018-02-23T18:32:09Z (GMT). No. of bitstreams: 1 santos_sp_me_sjrp.pdf: 1777749 bytes, checksum: 414449c29a5a2c7be6d6e5dc4eb7fbe0 (MD5) Previous issue date: 2018-02-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Seja S uma superf´ıcie regular em R3 sem pontos parab´olicos. O conjunto focal de S ´e o lugar geom´etrico dos centros das esferas que possuem contato degenerado com S em cada ponto. Tal contato ´e medido pelas singularidades da fam´ılia de func¸˜oes distaˆncia ao quadrado D associada a` S. O conjunto focal ´e uma superf´ıcie, por´em n˜ao necessariamente regular, e pode tamb´em ser visto como o conjunto bifurca¸ca˜o da fam´ılia D. A t´ecnica de associar uma variedade singular X(S) a uma subvariedade suave S do espa¸co euclidiano e descobrir alguns aspectos da geometria de S a partir daqueles de X(S) esta´ na essˆencia das aplica¸co˜es da Teoria das Singularidades `a Geometria Diferencial. Neste trabalho, estudamos os modelos, a menos de difeomorfismos, para o conjunto focal de superf´ıcies imersas em R3 gen´ericas, reunimos os principais resultados sobre a geometria da superf´ıcie focal encontrados na literatura e os apresentamos de forma mais explicativa e com uma linguagem moderna. Al´em disso, mostramos que a superf´ıcie focal pode ser parametrizada por uma frente de onda e utilizamos resultados conhecidos para tais aplica¸co˜es no estudo da geometria da superf´ıcie focal. / Let S be a immersed surface in R3 without parabolic points. The focal set of S is the locus of the centres of spheres that have a degenerate contact with S in each point. This contact is measured by singularities of the family of distance squared function D associated with S. The focal set is a surface, but is not necessarily regular, and it can also be seen as the bifurcation set of the family D. The approach of associating a singular variety X(S) to a smooth submanifold S in an Euclidian space and recover some aspects of the geometry of S from that of X(S) is at the essence of applications of singularity theory to the Differential Geometry. In this work, we study models, unless diffeomorphism, of focal set of the immersed generics surfaces in R3. We have also gathered some results about the geometry of the focal set of the literature and we present them in a more explanatory way and in a modern notation. Furthermore, we show that the focal surface can be parametrized by a wave front and use the known results of such applications in the study of the focal set. / Fapesp: 2016/21226-5
9

Análise das singularidades da função de dois pontos do campo quântico escalar localizado tipo-string

Santos, José Amâncio dos 16 June 2010 (has links)
Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-26T17:28:14Z No. of bitstreams: 1 joseamanciodossantos.pdf: 408905 bytes, checksum: 5a4696372063642f4350d6dbd066da13 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T20:37:22Z (GMT) No. of bitstreams: 1 joseamanciodossantos.pdf: 408905 bytes, checksum: 5a4696372063642f4350d6dbd066da13 (MD5) / Made available in DSpace on 2017-08-07T20:37:22Z (GMT). No. of bitstreams: 1 joseamanciodossantos.pdf: 408905 bytes, checksum: 5a4696372063642f4350d6dbd066da13 (MD5) Previous issue date: 2010-06-16 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Como é bem conhecido, os campos quânticos estudados na TQC satisfazem o princípio de localidade segundo pontos do espaço-tempo. Entretanto, os príncipios da física também admitem campos quânticos que satisfazem a uma condição de localidade determinada por strings 1, as quais são semi-retas no espaço-tempo partindo de algum ponto (evento) e se estendendo em alguma direção do tipo espaço. Devido a esta noção de localidade via string, dizemos que tais campos possuem localização do tipo-string. Por outro lado, nos referimos aos campos cuja localidade é caracterizada por pontos do espaço-tempo, dizendo que eles possuem localização do tipo-ponto ou que são puntiformemente localizados. O interesse na localização do tipo-string está na possibilidade de campos com tal localização apresentarem um comportamento UV, isto é, em altas energias, menos singular do que os campos com a localização do tipo-ponto, permitindo assim a obtenção de mais modelos interagentes com localização do tipo-string. Campos livres com localização tipo-string já foram obtidos para vários tipos de partículas [1, 2], a partir dos quais pode-se construir modelos interagentes. No entanto, para realizar esta tarefa, ou seja, construir modelos com interação a partir do campo livre, deve-se fazer uma análise da função de dois pontos do campo livre correspondente. Neste ponto se faz necessário o uso de certos conceitos e instrumentos - por exemplo: suporte singular, wave front set e scaling degree - na análise da função de dois pontos. Neste texto procuramos introduzir estes conceitos e instrumentos. Além disso, consideramos um modelo de campo escalar livre com localização do tipo-string para uma partícula massiva com spin nulo, para o qual apresentamos e procuramos analisar a estrutura de singularidades da função de dois pontos correspondente, dando uma interpretação em termos de strings. / As is well-known, the quantum fields studied in QFT satisfy the principle of locality according to points in space-time. However, the principles of physics also admit quantum fields that satisfy a condition of locality determined by strings2, which are rays (semi axes) in space-time starting from some point (event) and extending in some space-like direction. Due to this notion of locality via string, we say that such fields are string-localized. On the other hand, we refer to fields whose locality is characterized by points in space-time, saying that they are localized on points. The interest in string localization is the possibility that fields with such kind of localization present a less singular UV behaviour, that is, at high energy, than that of fields localized on points, and then permitting the construction of more interacting models. String-localized free quantum fields have been constructed for many particles types [1, 2], from which one can construct interacting models. However, in order to do this, that is, to construct interacting models from the free fields, it is necessary to analyse the two point function of the corresponding free fields. At this point we have to use some concepts and tools - for example: singular support, wave front set and scaling degree - to analyse the two point function. In this text we introduce these concepts and tools. Moreover, we consider a string-localized free scalar quantum field model for a massive spin zero particle, for which we present and analyse the singularity structure of the corresponding two point function, giving a interpretation in terms of strings.
10

Daylight operation of a sodium laser guide star

Hart, Michael, Jefferies, Stuart, Murphy, Neil 27 July 2016 (has links)
We report photometric measurements of a sodium resonance guide star against the daylight sky when observed through a tuned magneto-optical filter (MOF). The MOF comprises a sodium vapor cell in a kilogauss-level magnetic field between crossed polarizers and has a very narrow transmission profile at the sodium D-2 resonance of approximately 0.008 nm. Our observations were made with the 1.5 m Kuiper telescope on Mt. Bigelow, AZ, which has a separately mounted guide star laser projecting a circularly polarized single-frequency beam of approximately 6.5 W at 589.16 nm. Both the beam projector and the 1.5 m telescope were pointed close to zenith; the baseline between them is approximately 5 m. Measurements of the guide star were made on the morning of 2016 March 24 using an imaging camera focused on the beacon and looking through the full aperture of the telescope. The guide star flux was estimated at 1.20x10(6) photon/m(2)/s while at approximately 45 minutes after sunrise, the sky background through the MOF was 1100 photon/m(2)/s/arcsec(2). We interpret our results in terms of thermal infrared observations with adaptive optics on the next generation of extremely large telescopes now being built.

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