Dissertations / Theses on the topic 'Coronagraphie'
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SCHMITTE, RIVEZ ANNICK. "Interets du doppler des membres inferieurs avant coronagraphie." Reims, 1992. http://www.theses.fr/1992REIMM067.
Alagao, Mary Angelie. "Characterization and optimization of the Evanescent Wave Coronagraph." Electronic Thesis or Diss., Saint-Etienne, 2023. http://www.theses.fr/2023STET0060.
Direct imaging of exoplanets remains challenging due to the high contrast and the small angular separation between the star and the planet. It requires suppressing the blinding glare from the star and ensuring that the planet's faint light is not buried deep in various noises. Successful detection depends on the technological readiness and maturity of techniques and algorithms employed while considering the significant trade-offs on raw contrast, inner working angle, and throughput. One of its key components is the use of coronagraphs – instruments with the sole purpose of blocking/reducing the light from the star. This work presents a new type of Lyot coronagraph, invented by Dr. Yves Rabbia, that relies on the frustrated total internal reflection (FTIR) principle to suppress the starlight. This coronagraph is aptly called the Evanescent Wave Coronagraph (EvWaCo) owing to its nature that its focal plane mask, comprising a lens and a prism, reflects the off-axis source (planet) and transmits the on-axis source (star) by capturing the evanescent waves. This thesis aims to provide the reader with the groundwork that highlights EvWaCo's three main advantages: i) the mask is inherently achromatic, ii) the size of the mask is adjustable by changing the pressure between the lens and the prism, and iii) both the stellar light and the planet light can be collected simultaneously for low-order wavefront sensing, and proper stellar light centering. The performance of EvWaCo is assessed through experiments in a laboratory and then compared to numerical simulations. The experimental results show a raw contrast equal to a few 10-4 at 3 ��/�� over the full I-band (��c = 800 nm, ∆��/�� ≈ 20%) and at 4 ��/�� over the full R-band (��c = 650 nm, ∆��/�� ≈ 23%). The simulations confirm the achromatic rejection capability of EvWaCo as it showed a raw contrast of 10-4 at the same radial distance over both bandpasses. This thesis concludes with the status of its testbed and future perspectives
Chipman, Russell A. "Challenges in coronagraph optical design." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/627190.
Xin, Yeyuan(Yeyuan Yinzi). "Coronagraphic data post-processing using projections on instrumental modes." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127114.
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 71-76).
High contrast astronomy has yielded the direct observations of over a dozen exoplanets and a multitude of brown dwarfs and circumstellar disks. Despite advances in coronagraphy and wavefront control, high contrast observations are still plagued by residual wavefront aberrations. Post-processing techniques can provide an additional boost in separating residual aberrations from an astrophysical signal. This work explores using a coronagraph instrument model to guide post-processing. We consider the propagation of signals and wavefront error through a coronagraphic instrument, and approach the post-processing problem using "robust observables." We model and approximate the instrument response function of a classical Lyot coronagraph (CLC) and find from it a projection that removes the dominant error modes.
We use this projection to post-process synthetically generated data, and assess the performance of the new model-based post-processing approach compared to using the raw intensity data by calculating their respective flux ratio detection limits. We extend our analysis to include the presence of a dark hole using a simulation of the CLC on the High-contrast imager for complex aperture telescopes (HiCAT) testbed. We find that for non-time-correlated wavefront errors, using the robust observables modestly increases our sensitivity to the signal of a binary companion for most of the range of separations over which our treatment is valid, for example, by up to 50% at 7.5[lambda]/D. For time-correlated wavefront errors, the results vary depending on the test statistic used and degree of correlation. The modest improvement using robust observables with non-time-correlated errors is shown to extend to a CLC with a dark hole created by the stroke minimization algorithm.
Future work exploring the inclusion of statistical whitening processes will allow for a more complete characterization of the robust observables with time-correlated noise. We discuss the dimensionality of coronagraph self-calibration problem and motivate future directions in the joint study of coronagraphy and post-processing.
by Yeyuan (Yinzi) Xin.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics
Pueyo, Laurent, Neil Zimmerman, Matthew Bolcar, Tyler Groff, Christopher Stark, Garreth Ruane, Jeffrey Jewell, et al. "The LUVOIR architecture ``A'' coronagraph instrument." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626292.
Thompson, Samantha Jayne. "OSCA, an Optimised Stellar Coronagraph for Adaptive optics." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1338360/.
Chipman, Russell A. "Image formation in coronagraphs due to mirror polarization aberrations." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/627180.
Mawet, D., P. Wizinowich, R. Dekany, M. Chun, D. Hall, S. Cetre, O. Guyon, et al. "Keck Planet Imager and Characterizer: concept and phased implementation." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622026.
Knight, Justin M., John Brewer, Ryan Hamilton, Olivier Guyon, Thomas D. Milster, and Karen Ward. "Design, fabrication, and testing of stellar coronagraphs for exoplanet imaging." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/627078.
Martinache, Frantz, Nemanja Jovanovic, and Olivier Guyon. "Subaru Coronagraphic eXtreme Adaptive Optics: on-sky performance of the asymmetric pupil Fourier wavefront sensor." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622025.
Newman, Kevin, Dan Sirbu, Ruslan Belikov, and Olivier Guyon. "Development of PIAA Complex Mask Coronagraphs for large aperture ground-based telescopes." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622426.
Martinez, Patrice. "Coronagraphs characterization for high-contrast imaging in the context of extremely large telescopes." Paris 7, 2008. http://www.theses.fr/2008PA077208.
This thesis was realized in the context of exoplanet direct detection with ground-based extremely large telescopes (30 to 42 meter diameter). To deliver such contrast level, adaptive/optics System (to correct for the turbulence aberrations) and coronagraphs (to reduce the flux of the parent star where the planet signal is hidden) are required. The intent of this study is to optimize, compare and select optimal coronagraph concepts that can accommodate such telescope constraints (primary mirror obscuration and segmentation, secondary holder. . . ) at several contrast levels (after correction of the atmospheric turbulence with an adaptive optics System, and when a calibration of the halo is performed by the use of a differential imaging System). Finally, prototyping details are described for several coronagraphs that will be implemented on an adaptive optics testbench, as well as the development of a new technical solution for the manufacture of apodizers (critical components for several coronagraph concepts)
Absil, Olivier, Dimitri Mawet, Mikael Karlsson, Brunella Carlomagno, Valentin Christiaens, Denis Defrère, Christian Delacroix, et al. "Three years of harvest with the vector vortex coronagraph in the thermal infrared." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622801.
Bush, Nathan L. "The impact of radiation damage on electron multiplying CCD technology for the WFIRST coronagraph." Thesis, Open University, 2018. http://oro.open.ac.uk/55053/.
Otten, Gilles P. P. L., Frans Snik, Matthew A. Kenworthy, Christoph U. Keller, Jared R. Males, Katie M. Morzinski, Laird M. Close, et al. "ON-SKY PERFORMANCE ANALYSIS OF THE VECTOR APODIZING PHASE PLATE CORONAGRAPH ON MagAO/Clio2." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624015.
Forsberg, Pontus. "Diamond Microfabrication for Applications in Optics and Chemical Sensing." Doctoral thesis, Uppsala universitet, Mikrosystemteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-192567.
Vassallo, Daniele. "A virtual coronagraphic test bench for SHARK-NIR, the second-generation high-contrast imager for the Large Binocular Telescope." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3422319.
SHARK-NIR è l'imager ad alto contrasto di seconda generazione per il Large Binocular Telescope. Durante il mio Ph.D. sono stato coinvolto nella fasi di design concettuale e finale dello strumento. In specifico, ho sviluppato un simulatore in IDL che è stato utilizzato come banco di test virtuale per realizzare uno studio comparativo di diverse tecniche coronografiche identificate come possibili candidate a essere implementate nello strumento. Il simulatore è basato sulla propagazione di fronti d'onda e utilizza un approccio end-to-end per generare immagini in presenza di svariate sorgenti di aberrazioni ottiche, da residui atmosferici a vibrazioni e aberrazioni di non-common path (NCPA). Un'attenzione particolare è stata rivolta all'ottimizzazione del software attraverso specifici schemi di parallelizzazione, alla modellizzazione delle proprietà temporali e spaziali delle NCPA e allo studio dell'impatto del prossimo upgrade dei sistema di Ottica Adattiva di LBT. Ho esplorato le performance di diversi coronografi in un ampio range di condizioni osservative e caratterizzato la loro sensibilità ad aberrazioni, disallineamenti e cromatismo. Ho anche contribuito allo sviluppo di una pipeline di riduzione dati rivolta a processare le immagini simulate adottando diversi algoritmi. I risultati delle simulazioni sono stati utilizzati per effettuare una selezione di tecniche coronografiche in grado di soddisfare i requisiti scientifici dello strumento. Infine, ho validato attraverso simulazioni un approccio denominato Phase Diversity il cui fine è misurare on-line le NCPA. Le simulazioni hanno contribuito alla scelta di implementare uno specchio deformabile interno per la correzione simultanea di NCPA e vibrazioni residue ad alta frequenza.
Mawet, Dimitri, Élodie Choquet, Olivier Absil, Elsa Huby, Michael Bottom, Eugene Serabyn, Bruno Femenia, et al. "CHARACTERIZATION OF THE INNER DISK AROUND HD 141569 A FROM KECK/NIRC2 L-BAND VORTEX CORONAGRAPHY." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625206.
Chipman, Russell A. "Advances in modeling polarimeter performance." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626492.
Newman, Kevin, and Kevin Newman. "Achromatic Phase Shifting Focal Plane Masks." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621110.
Estevez, Dimitri. "Keplerian-Stacker: A new technique for coronagraphic images to increase the signal to noise ratio and detect exoplanets with direct imagning instruments." Thesis, KTH, Fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210306.
Stenborg, Guillermo Adrián. "Interpretation and analysis on various time scales of narrow band coronal oberservations obtained with a new coronagraph system." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=963589644.
Braga, Carlos Roberto. "Study of solar-interplanetary-geomagnetic disturbances using data from the Global Muon Detector Network and the LASCO coronagraph." Instituto Nacional de Pesquisas Espaciais, 2011. http://urlib.net/sid.inpe.br/mtc-m19/2011/02.07.20.31.
The objective of this work is to study solar-interplanetary-geomagnetic disturbances like coronal mass ejections (CMEs) using observations from the white light coronagraph and high-energy cosmic ray (muons). Images from the Large Angle and Spectroscopic Coronagraph (LASCO-C3) were segmented by texture in a supervised way and the identified contour was used to estimate the radial and expansion speed of a set of 57 limb CMEs for the period between 1997 and 2001. Texture analysis was chosen in a way to parameterize the estimation of CMEs contours, which are not always consensus. In a general view, the identified contour is in agreement with the CME definition and the estimate position angle, radial speed and expansion speed are in agreement with previous catalogs manually done. In the other hand, using high-energy cosmic ray (muons) observations, signatures preceding the arrival of plasma structures were studied using data from the Global Muon Detector Network (GMDN). Pitch angle distributions were done for periods associated with the 16 small and moderate geomagnetic storms observed in 2008. Fourteen of them show some possible precursors, both precursory increases and precursory decreases. No clear reason was found yet for not seeing precursors in the remaining two events.
Braga, Carlos Roberto. "Study of coronal mass ejections and their corresponding interplanetary structures using combined observations of cosmic ray detectors and coronagraphs." Instituto Nacional de Pesquisas Espaciais (INPE), 2015. http://urlib.net/sid.inpe.br/mtc-m21b/2015/01.30.19.09.
O objetivo desta Tese é estudar ejeções coronais de massa (conhecidas pela sigla CME, da expressão em Língua Inglesa, coronal mass ejections) e suas correspondentes estruturas interplanetárias usando observações de sensoriamento remoto da coroa solar, dados de campo magnético e plasma in situ do meio interplanetário e observações de detectores de raios cósmicos instalados na superfície da Terra. As CMEs têm um papel central na relação Sol-Terra porque elas são uma das principais causadoras de tempestades geomagnéticas. Iniciou-se a análise desta Tese a partir de uma lista de nuvens magnéticas observadas entre 2008 e 2011 nas vizinhanças da Terra. Uma vez caracterizadas as estruturas interplanetárias, identificaram-se as CMEs ejetadas no período e direção apropriados para produzir cada uma das nuvens magnéticas. A direção das CMEs pode ser estudada graças a observação simultânea da coroa solar a partir de três pontos de observação distintos: um proveniente do instrumento LASCO (\emph{Large Angle and Spectroscopic Coronagraph}) e outros dois do SECCHI (\emph{Sun Earth Connection Coronal and Heliospheric Investigation}). Desenvolveu-se um novo método para rastrear as CMEs em três dimensões usando o rastreio pseudo-automático por textura, triangulação e pontos de amarra. Para cada CMEs, estimou-se a velocidade tridimensional (tanto a magnitude como a direção) usando o novo método e, nos casos já abordados em trabalhos anteriores, compararam-se os resultados. Por outro lado, combinando-se observações de quatro detectores de raios cósmicos (múons), deduziu-se o gradiente da densidade dos raios cósmicos para todos os casos de nuvens magnéticas observadas e, por conseguinte, estimou-se a sua posição geral. Em alguns casos, ajustou-se um modelo da distribuição dos raios cósmicos no interior da nuvem magnética com os dados observados e deduziram-se outras propriedades da nuvem magnética, como orientação e diâmetro. Finalmente, para cada caso, resultados obtidos na coroa solar foram comparados com aqueles deduzidos por observações de raios cósmicos.
Femenía, Castellá Bruno, Eugene Serabyn, Dimitri Mawet, Olivier Absil, Peter Wizinowich, Keith Matthews, Elsa Huby, et al. "Commissioning and first light results of an L'-band vortex coronagraph with the Keck II adaptive optics NIRC2 science instrument." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622007.
Kosová, Petra. "Numerické metody zpracování obrazů z kosmického koronografu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400457.
Hinrichs, Johannes [Verfasser]. "Analysis of Space Weather Impacts on the Terrestrial Ionosphere and Development and Testing of a Coronagraph for Space Weather Forecasts / Johannes Hinrichs." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1214440207/34.
Jovanovic, N., O. Guyon, J. Lozi, T. Currie, J. Hagelberg, B. Norris, G. Singh, et al. "The SCExAO high contrast imager: transitioning from commissioning to science." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622018.
Rougeot, Raphaël. "Calculs de diffraction pour les coronographes solaires en vol en formation : Application pour ASPIICS." Thesis, Université Côte d'Azur, 2020. https://tel.archives-ouvertes.fr/tel-03177643.
The future formation flying PROBA-3 ESA mission will fly the giant solar coronagraph ASPIICS. One spacecraft will carry an occulter disc of 1.42m diameter in front of the Sun. It will cast its shadow onto the 5cm aperture of a Lyot-style coronagraph on-board a second spacecraft that will be positioned 150m behind with millimeters accuracy. ASPIICS aims to observe the solar corona in the rather unexplored region from 1.1 to 3.0 solar radii, where the coronal brightness is six to ten orders of magnitude lower than the solar disc. For such high-contrast instrument, straylight from sunlight diffraction is a key driver for the performance. Dedicated and accurate modeling of these diffraction effects are thus required. Additionally, the novel concept of formation flying brings new constraints to be investigated.This thesis aims to meet these needs. The method is numerical. First, the diffraction from the occulter is calculated by models designed for the study case. The umbra is computed as an incoherent summation over the solar disc. Second, the Fresnel propagation of the diffracted wave front through the coronagraph is built upon Fourier optics, and uses 2D FFT with large arrays. Perturbations are finally added to the model, like roughness scattering from the telescope, or misalignment and off-pointing of the spacecraft flying formation. The end result is the spatial distribution of the diffracted sunlight intensity at detector level. Sizing the Lyot mask and stop and vignetting effects are also analyzed.Regarding the umbra intensity, the study shows that serrated occulters are better than the simple disc and can almost reach the straylight performance of the apodized disc. At detector level, the brightness of the diffraction at 1.1 solar radius remains similar to the corona. But the coronagraph manages to reduce the straylight to the required level beyond 1.3 solar radius. While the formation flying errors have a limited impact, the scattering significantly increases the diffraction in the outer field-of-view. These results have been used to support the design of ASPIICS
Venet, Melanie. "Coronographes spatiaux : Solar Orbiter / Metis, Smese / Lyot, Proba-3 / Aspiics." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10011.
The solar corona is the part of the Sun's atmosphere that extends from the photosphere (solar surface where the photons are emitted) into the interplanetary medium. Its understanding is a major issue because it is the source of phenomena that can disrupt telecommunications, living beings and even climate. The most appropriate tool to observe it is the coronagraph, an optical system obscuring the solar disk in favor of the corona, a million times fainter. My thesis deals with its review, particularly through the spaceprojects :- Solar Orbiter, which will approach the Sun at 0.2 astronomical unit (distance between Earth and Sun), allowing a very high spatial resolution ;- SMESE, in cooperation with China, which should study the corona in the Lymanalpha (and far infrared) ;- and ASPIICS, which will observe the corona in conditions close to a natural solar eclipse, with its occulting disk located at 150 m from the imaging instrument.The first point tackled is the rejection of instrumental stray light, whose optimization is one of the major problems in coronagraphy. The second concerns the methods of observation and imaging in white light, monochromatic imaging, and interferometry, in particular the Fabry Perot. The development and improvement of these techniques will allow considerable progress in terms of resolution and access to the corona ever closer to the Sun's surface, the location yet little known where the solar activity originates
Herscovici-Schiller, Olivier. "Analyse et correction de surface d’onde post-coronographique pour l’imagerie d’exoplanètes." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEO022/document.
Exoplanet imaging has two intrinsic limitations, namely the small angular separation between the star and the planet, and the very low light flux from the planet compared to the starlight. The first limitation is overcome by using very large telescopes of the ten-metre diameter class, and, for ground-based telescopes, adaptive optics systems, which allow high angular resolution imaging. The second limitation is overcome by using a coronagraph. Coronagraphs are optical devices which filter the starlight while granting passage to the light coming from the stellar environment. However, any optical aberration upstream of the coronagraph causes some of the starlight to leak through the coronagraph. This unfiltered starlight in turn causes speckles in the scientific images, and the light of the planets that could be there is lost among the speckles. Consequently, measurement and correction of the quasi-static aberration which generate the speckles are necessary for the exoplanet imagers to achieve their full potential. This thesis introduces theoretical, numerical, and experimental contributions to the topic of measurement and correction of the aberrations in coronagraphic imagers. The first part describes the context and introduces coronagraphic phase diversity, which is a Bayesian inverse problem formalism for post-coronagraphic wave-front sensing. The second part is focused on ground-based imaging. It introduces an analytic expression for coronagraphic imaging through turbulence, the extension of coronagraphic phase diversity to on-sky measurement through residual turbulence, and a laboratory validation of the extended method. The third part is concerned with future high-contrast space-based imagers, which will require not only phase correction, but a full complex wave-front correction. It presents the laboratory validation of coronagraphic phase diversity as a post-coronagraphic complex wave-front sensor, and first results of active contrast enhancement in the focal plane through thecreation of a non-linear dark hole
Anzolin, Gabriele. "Astronomical applications of optical vortices." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426036.
I vortici ottici rappresentano una particolare classe di dislocazioni dei fronti d'onda caratterizzate da una carica topologica l. La superficie di fase costante di un'onda elettromagnetica che trasporta un vortice ottico ha una struttura elicoidale. Lungo l'asse di questa elica è presente una singolarità in cui la fase non può essere definita. Di conseguenza, la distribuzione d'intensità di un fascio di luce contenente un vortice ottico presenta una zona centrale dove l'intensità è nulla per effetto dell’interferenza distruttiva. I vortici ottici possono essere prodotti utilizzando particolari elementi ottici detti phase modifying devices che modificano la fase di un'onda incidente. I più efficienti tra questi sono i fork holograms (ologrammi) e le spiral phase plates (maschere di fase). Negli ultimi anni, le proprietà dei vortici ottici hanno trovato interessanti applicazioni nei campi della fisica e dell'ottica. Tra queste, le più promettenti sono quelle in comunicazioni ottiche, nelle nanotecnologie ed in biologia. Recentemente, i vortici ottici stanno suscitando un crescente interesse anche nella comunità astronomica. Infatti, queste particolari proprietà della radiazione elettromagnetica potrebbero permettere di studiare diversi fenomeni astrofisici da un punto di vista completamente nuovo. In questa Tesi vengono presentate alcune possibili applicazioni dei vortici ottici in strumentazione astronomica. In particolare, lo scopo principale di questo lavoro è lo sviluppo di nuove tecniche che permetteranno di migliorare le prestazioni di sistemi ottici. In primo luogo, viene proposto un metodo per aumentare il potere risolutivo di un telescopio limitato dalla diffrazione che prevede l'utilizzo di un fork hologram con una singola dislocazione. I risultati di esperimenti e simulazioni numeriche rivelano che la sovrapposizione dei vortici ottici prodotti da due fasci di luce con una distribuzione d'intensità di Airy mostra già un'evidente asimmetria quando la separazione è di un ordine di grandezza inferiore rispetto al limite posto dal criterio di Rayleigh. Questo risultato è stato ottenuto sia in luce monocromatica, sia in luce bianca. Viene poi presentato il primo esperimento astronomico in cui sono stati prodotti vortici ottici con un fork hologram avente una singola dislocazione posto al piano focale del telescopio Galileo da 122 cm di Asiago. Utilizzando i principi del Lucky Imaging per ridurre gli effetti provocati da condizioni di seeing mediocre, sono state osservate le immagini dei vortici ottici prodotti dalle due componenti principali del sistema multiplo alfa Her, in luce non monocromatica, e dalla stella singola alfa Boo, utilizzando un filtro spaziale a banda stretta. In entrambi i casi, i profili d’intensità dei vortici ottici osservati sono riproducibili con simulazioni numeriche. La sensibilità dell'immagine di un vortice ottico prodotto con un phase modifying device rispetto a spostamenti fuori asse del fascio entrante è confermata da modelli analitici dettagliati e anche da simulazioni numeriche, specialmente nel caso in cui vengano utilizzati elevati valori della cariche topologica l. Questa proprietà potrebbe essere utilizzata per fare misure astrometriche da terra con una precisione che potrebbe competere con quella fornita dalle tecniche standard di astrometria di PSF. La sensibilità rispetto a piccoli spostamenti fuori asse potrebbe anche essere sfruttata per migliorare la correzione dell’aberrazione di tip/tilt del fronte d'onda in un piccolo campo di vista. Viene poi discussa la possibile applicazione di vortici ottici con carica topologica pari nella coronografia ad alto contrasto. In questo caso, l'azione combinata di una spiral phase plate e di un diaframma circolare utilizzato come stop di Lyot permette di annullare totalmente la luce di una stella in asse. Studi teorici indicano che il coronografo a vortici ottici è uno dei pochi che potrebbe realmente permettere l'osservazione diretta di pianeti extrasolari di tipo terrestre. Purtroppo, questa notevole proprietà è fortemente limitata dalle attuali tecniche usate per produrre le spiral phase plate. Nell'ambito di un progetto di costruzione di un coronografo a vortici ottici con l = 2 ottimizzato per lunghezze d'onda visibili, vengono presentati i risultati di simulazioni numeriche ottenuti considerando una spiral phase plate la cui superficie è suddivisa in N livelli discreti. Infine, vengono discusse le procedure sperimentali utilizzate per testare spiral phase plates in PMMA (polimetil-metacrilato).
Paul, Baptiste. "Mesure de front d'onde post-coronographique à haute précision pour l'imagerie à haut contraste : appplication sol et espace." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4731/document.
Performing an exoplanet direct detection means being able to image an object as faint as an extra-solar planet very close to its parent star. After compensation of the turbulence by the XAO loop and most of the star light removed by a coronagraph, the ultimate limitation of high contrast imaging systems lies in its quasi-static aberrations that creates a residual signal which limit the achievable contrast on the scientific detector. To increase the achievable contrast on the detector, these aberrations must be compensated for, ideally using focal plane data recorded from the scientific detector to avoid differential aberrations. The aim of this thesis was to develop a focal-plane wavefront sensor (WFS) dedicated to the estimation of quasi-static aberrations in high contrast imaging systems. This WFS, called COFFEE, estimates the aberrations both upstream and downstream of the coronagraph using coronagraphic focal plane images that differ from a known diversity aberrations introduced upstream of the coronagraph. During this research work, COFFEE has been developed, tested using numerical simulations and demonstrated on an in-house bench. Considering the limitations of the estimation accuracy, COFFEE's formalism has then been modified to allow it to estimate high frequencies aberrations with nanometric precision. This extended version of COFFEE has been successfully used on SPHERE to optimize the contrast on the scientific detector of the instrument using COFFEE in a dedicated compensation process. Lastly, a new compensation method has been developed in order to reach very high contrast levels on the scientific detector
Bourget, Pierre. "Coronographie à masque adaptatif pour imagerie et détection à haute dynamique." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4375.
High contrast imaging of extra-solar planets and environments of bright astro- physical objects in general, such as stars, active galactic nuclei or objects of the Solar System is a challenging task. Different approaches are needed if the bright region to occult is optically resolved or not. We present the Adaptive Mask concept, observations on sky and numerical simulations show the usefulness of the proposed methods to optimize the efficiency of the coronagraphs for optically resolved or non resolved objects. Accessing small IWA is considered as an edge as it provides substantial scientific and technical advantages. One of the difficulties of accessing small IWA is that coronagraphs become very sensitive to low-order aberrations such as tip-tilt. Our original approach aims at integrating the small IWA capability and the mitigation of sensitivity to low-order aberrations within the coronagraph itself. Our concept is applicable to both low and high Strehl regimes, corresponding to current and next generation AO systems. The adaptive coronagraph can adapt dynamically, in quasi real time, to adjust to the observing conditions to deliver a stable and optimized contrast at the science image level. The mask adaptability both in size, phase and amplitude also compensates for manufacturing errors of the mask itself, and potentially for chromatic effects. The mask adaptability concept using a local phase modulation in the focal plane allows synchronous modulation for high dynamic range synchronous detection of a faint target immersed in a background. The coherence of the speckles with the central star is used to discriminate them from proper companions
Laugier, Romain. "Observables robustes pour la détection haut-contraste à faible séparation angulaire." Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4046.
The study of exoplanets has been a very active topic in the past years. Despite the indirect nature of most detections to date, those already provide us with a wealth of information on the properties of these exoplanetary systems, like their mass, size, and orbital elements. However, the direct detection of the light emitted or reflected by those planets provides some even more precious information. Coronagraphic instruments that would allow this are generally limited by the wavefront quality at their input, which prevents them from reaching their theoretical performance. Conversely, techniques employing observables designed to be robust to those aberrations are limited by photon noise. These two methods are made incompatible because coronagraphy breaks the convolution relationship betwen the object and its image. The works described in this thesis explore different avenues aiming to sidestep this incompatibility and to combine the performance of coronagraphic and interferometric methods though technology transfers as well as the development of new methods. The development of angular differential kernel phases (ADK) that make use the principles of angular differential imaging (ADI), transfering them for kernel and closure phases observables. The experimentation of kernel phases behind shaped pupil apodization masks. The exploitation kernel phases extracted from archival saturated images. The development of architectures for kernel nulling for an arbitrary number of apertures for Fizeau and long-baseline interferometry. These works push the contrast performance of robust observables at small angular separations and begin the exploration of new methods of robust high-contrast observations
Mari, Elettra. "Optical vortex diffractive optics for terrestrial and space applications." Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422490.
I vortici ottici, sono caratteristiche topologiche dell’onda, legate alle singolaritá di fase nei campi elettromagnetici che trasportano momento angolare orbitale (OAM). Il fronte d’onda ha forma elicoidale, si attorciglia spiraleggiando attorno all’asse di propagazione in cui la fase é indefinita. Lungo l’asse dell’elica le onde fanno interferenza distruttiva le une con le altre, con il risultato di una distribuzione d’intensitá caratterizzato da una regione buia nel centro, circondata da luce a forma di ciambella. I vortici ottici sono caratterizzati da un valore, detto carica topologica che indica quante volte la fase compie una completa variazione di 360 gradi attorno all’asse ottico in una lunghezza d’onda. I vortici ottici possono essere prodotti con l’utilizzo di strumenti ottici. In particolare in questa tesi sono state studiate delle particolare ottiche diffrattive dette spirali di fase. Le spirali di fase sono ottiche il cui spessore cresce gradualmente intorno ad un asse; somigliano a scale a chioc- ciola, costruite con un certo numero di scalini ed impongono al fascio incidente un ritardo di fase che dipende dall’angolo azimutale. L’oggetto di questa ricerca é lo studio delle proprietá delle spirali di fase, la caratterizzazione e alcune possibili applicazioni. Lo studio si é inizialmente concentrato sulle spirali da fase nel range del visibile. Attraverso simulazioni numeriche ed esperimenti al banco ottico, siamo riusciti a ricavare una relazione tra il numero degli scalini che costruiscono il salto di fase nella spirale e la carica topologica che viene imposta al fascio incidente. Questo risultato ci ha permesso di ottimizzare i parametri di costruzione della spirale realiz- zata in PMMA per applicazioni astronomiche. Abbiamo infatti assemblato il primo prototipo di un coronografo a vortici ottici, nel cui cammino ottico é stata inserita la spirale di fase realizzata in base ai parametri da noi definiti. I coronografi, in generale, sono strumenti progettati per bloccare la luce proveniente da una sorgente brillante in modo tale da poter osservare direttamente delle sorgenti piú deboli nelle vicinanze. Il coronografo a vortici ottici sfrutta la regione buia nella di- stribuzione d’intensitá di un vortice ottico per attenuare la luce di una sorgente luminosa, senza diminuire l’intensitá della sorgente secondaria. Abbiamo testato il nostro prototipo al telescopio ’Galileo’ 122cm di Asiago, attenuando l’in- tensitá di una componente del sistema stellare doppio Epsilon2 Lyrae di quasi un ordine di magnitudine. L’applicazione astronomica della spirale di fase ci ha spinto allo studio delle sua efficienza, ovvero del contrasto che si ottiene nella zona buia del vortice ottico, a diverse distanze angolari della sorgente secondaria rispetto alla singolaritá centrale della spirale. Simulazioni numeriche hanno mostrato che il coronografo a vortici ottici funziona anche al di sotto del limite di risoluzione di Rayleigh. La ricerca si é sviluppata fino alla formulazione di un nuovo metodo per determinare la distanza angolare tra due sorgenti distanti meno del criterio di Rayleigh. Il nuovo metodo sfrutta la distribuzione d’intensitá asimmetrica dei vortici ottici prodotti dalla sorgente secondaria che passa attraverso la spirale di fase, ma non in corrispondenza della singolaritá centrale. Poiché le equazioni di Maxwell sono valide su tutto lo spettro elettromagnetico, i vortici posso- no essere prodotti anche in diverse bande rispetto al visibile. Basandoci su questo fondamentale principio abbiamo studiato delle ottiche diffrattive per la produzione di vortici nel range del radio. Abbiamo costruito con polistirolo e alluminio una spirale di fase basandoci sui risultati trovati nel visibile ed abbiamo ottenuto la prima evidenza sperimentale di un vortice radio. La verifica speri- mentale della possibilitá di generare e sfruttare vortici radio ha spianato la strada all’esperimento successivo che é stato condotto nel campo della comunicazione radio. Abbiamo compiuto la prima trasmissione OAM in cui due segnali sono stati trasmessi con- temporaneamente e sulla stessa frequenza, su due canali radio codificati in due diversi stati di momento angolare orbitale. Questa nuova tecnica radio permette, in teoria, di codificare un infinito numero di canali in una singola banda centrata su una frequenza. I risultati dei nostri esperimenti nel dominio del radio aprono nuove prospettive nel mondo della comunicazione.
Hinrichs, Johannes. "Analysis of Space Weather Impacts on the Terrestrial Ionosphere and Development and Testing of a Coronagraph for Space Weather Forecasts." Doctoral thesis, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-1429-7.
Stenborg, Guillermo Adrian. "Interpretation and Analysis on Various Time Scales of Narrow-Band Coronal Oberservations Obtained with a New Coronagraph System." Doctoral thesis, 2000. http://hdl.handle.net/11858/00-1735-0000-0022-5D6F-1.
Douglas, Ewan S. "Advancing spaceborne tools for the characterization of planetary ionospheres and circumstellar environments." Thesis, 2016. https://hdl.handle.net/2144/19717.
Stenborg, Guillermo Adrián [Verfasser]. "Interpretation and analysis on various time scales of narrow band coronal oberservations obtained with a new coronagraph system / vorgelegt von Guillermo Adrián Stenborg." 2000. http://d-nb.info/963589644/34.