Academic literature on the topic 'Imaging atmospheric cherenkov telescopes'

The field of ground-based γ-ray astronomy has made very significant advances over the last three decades with the extremely successful operations of several atmospheric Cherenkov telescopes worldwide. The advent of the imaging Cherenkov technique for indirect detection of cosmic γ rays has immensely contributed to this field with the discovery of more than 220 γ-ray sources in the Universe. This has greatly improved our understanding of the various astrophysical processes involved in the non-thermal emission at energies above 100 GeV. In this paper, we summarize the important results achieved by the Indian γ-ray astronomers from the GeV-TeV observations using imaging Cherenkov telescopes over the last two decades. We mainly emphasize the results obtained from the observations of active galactic nuclei with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) telescope, which has been operational since 1997 at Mount Abu, India. We also discuss the future plans of the Indian γ-ray astronomy program with special focus on the scientific objectives of the recently installed 21 m diameter MACE (Major Atmospheric Cherenkov Experiment) telescope at Hanle, India.

ABSTRACT We propose a new approach, based on the Hanbury Brown and Twiss intensity interferometry, to transform a Cherenkov telescope to its equivalent optical telescope. We show that, based on the use of photonics components borrowed from quantum-optical applications, we can recover spatial details of the observed source down to the diffraction limit of the Cherenkov telescope, set by its diameter at the mean wavelength of observation. For this, we propose to apply aperture synthesis techniques from pairwise and triple correlation of sub-pupil intensities, in order to reconstruct the image of a celestial source from its Fourier moduli and phase information, despite atmospheric turbulence. We examine the sensitivity of the method, i.e. limiting magnitude, and its implementation on existing or future high energy arrays of Cherenkov telescopes. We show that despite its poor optical quality compared to extremely large optical telescopes under construction, a Cherenkov telescope can provide diffraction limited imaging of celestial sources, in particular at the visible, down to violet wavelengths.

High energy photons from astrophysical sources are unique probes for some predictions of candidate theories of Quantum Gravity (QG). In particular, Imaging atmospheric Cherenkov telescope (IACTs) are instruments optimised for astronomical observations in the energy range spanning from a few tens of GeV to ∼100 TeV, which makes them excellent instruments to search for effects of QG. In this article, we will review QG effects which can be tested with IACTs, most notably the Lorentz invariance violation (LIV) and its consequences. It is often represented and modelled with photon dispersion relation modified by introducing energy-dependent terms. We will describe the analysis methods employed in the different studies, allowing for careful discussion and comparison of the results obtained with IACTs for more than two decades. Loosely following historical development of the field, we will observe how the analysis methods were refined and improved over time, and analyse why some studies were more sensitive than others. Finally, we will discuss the future of the field, presenting ideas for improving the analysis sensitivity and directions in which the research could develop.

VERITAS is a ground-based gamma-ray observatory that uses the imaging atmospheric Cherenkov technique and operates in the very-high energy (VHE) region of the gamma-ray spectrum from 100 GeV to 50 TeV. The observatory consists of an array of four 12 m-diameter imaging atmospheric Cherenkov telescopes located in southern Arizona, USA. The four-telescope array has been fully operational since September 2007, and over the last two years, VERITAS has been operating with high reliability and sensitivity. It is currently one of the most sensitive VHE observatories. This paper summarizes the status of VERITAS as of October 2009, and describes the detection of several new VHE gamma-ray sources.

Silicon Photomultipliers (SiPMs) are excellent devices to detect the faint and short Cherenkov light emitted in high energy atmospheric showers, and therefore suitable for use in imaging air Cherenkov Telescopes. The high density Near Ultraviolet Violet SiPMs (NUV-HD3) produced by Fondazione Bruno Kessler (FBK) in collaboration with INFN were used to equip optical modules for a possible upgrade of the Schwarzschild-Couder Telescope camera prototype, in the framework of the Cherenkov Telescope Array project. SiPMs are 6×6 mm2 devices based on 40×40 μm2 microcells optimized for photo-detection at the NUV wavelengths. More than 40 optical modules, each composed by a 4×4 array of SiPMs, were assembled. In this contribution we report on the development and on the assembly of the optical modules, their validation and integration in the camera.

The subject of this thesis is the simulation study of the development of extensive air show ers produced by very high energy gamma-ray and hadronic cosmic rays with respect to the Cherenkov light they produce, and its imaging in ground based telescopes. Chapters 1-4 are introductory: Chapter 1 covers the mechanisms responsible for the production of very high energy gamma-rays, whereas, chapter 2 focusses on the development of extensive air showers and Cherenkov light production. Chapter 3 covers the instrumentation used to measure the Cherenkov light using the imaging atmospheric Cherenkov technique. Chapter 4 covers known and possible sources of very high energy gamma-rays. Chapters 5, 6 and 7 cover research performed by the author: Chapter 5 discusses some of the differences between three popular extensive air shower simulations codes, namely ALTAI, CORSIKA and MOCCA. Chapter 6 details the simulation of the response of two ground based imaging atmospheric Cherenkov telescope (the Durham Mark 6 and stand-alone H.E.S.S. telescopes), and in particular details the derivation of the flux of the x-ray selected BL-LAC PKS 2155-304 with the Durham Mark 6 telescope. This represents the refinement of a published measurement given an improved telescope simulation. The significance of the signal seen is 6.8o, and the integral flux derived above 1.5 TeV (assuming a differential spectral slope of-2.6) is {2.5±0.7stat ± (^0.5)(_1.6syst) x 10(^-7) photons m(^-2) s(^-1) Chapter 7 discusses the importance of the atmosphere, and the results of shower simulations under different atmospheric assumptions are presented, which indicate the importance of atmospheric calibration for the new generation of Cherenkov telescopes. The results of this chapter suggest that to first order large changes in the low level aerosol concentration have a much more significant effect on the trigger rate of a stand-alone H.E.S.S. telescope, than on the Hillas parameter distributions seen. Chapter 8 brings together the work done in this thesis, and highlights a final set of fluxes for the active galactic nuclei sources seen with the Durham Mark 6 telescope, many of which will form future sources to be measured with the H.E.S.S. system. The current status of the stand-alone H.E.S.S. system is also covered in chapter 8. The thesis concludes with a further brief discussion of the future prospects for imaging atmospheric Cherenkov astronomy.

Negli ultimi anni sono stati fatti grandi passi in avanti nel campo della muografia vulcanica. Questa tecnica sfrutta l'elevato potere penetrante dei muoni prodotti dall'interazione dei raggi cosmici primari con l'atmosfera terrestre per ricavare informazioni sulla struttura interna degli edifici vulcanici. La muografia permette di monitorare variazioni di densità utili a determinare lo stato di attività di un vulcano e ridurre il rischio associato. La principale difficoltà nell'applicazione della tecnica è data dal rumore di fondo di cui soffrono i rivelatori comunemente utilizzati. Per migliorare il rapporto segnale-rumore sono necessarie diverse lastre schermanti di piombo e ferro che rendono il rivelatore costoso e difficile da trasportare. Per far fronte a questi problemi, recentemente è stato proposto l'utilizzo di telescopi Cherenkov dedicati alla muografia. Questi non soffrono del rumore di fondo degli altri rivelatori e possono essere progettati con una struttura di supporto leggera e facilmente trasportabile. Questo lavoro di tesi si propone come uno studio preliminare di fattibilità necessario per lo sviluppo dell'ottica e dell'elettronica di un telescopio Cherenkov per la muografia vulcanica. A tal fine, ho sviluppato un software di simulazione basato su Geant4, un framework dedicato all'interazione delle particelle con la materia, che simula il passaggio dei muoni atmosferici attraverso un modello di edificio vulcanico e lo strato di atmosfera che lo separa dal telescopio, e la produzione di fotoni Cherenkov. Per studiare la rivelazione di questi, ho utilizzato il simulatore del prototipo di telescopio Cherenkov di piccola dimensione ASTRI SST-2M progettato per CTA e ho implementato un metodo per ricostruire la direzione dei muoni a partire dalle immagini ottenute con il simulatore. Il modello vulcanico utilizzato si basa sulle caratteristiche del Cratere Sud-Est del Monte Etna, il quale è visibile dal sito di installazione di ASTRI.

La naturalesa de la matèria fosca (DM) de l’univers segueix essent un misteri a dia d’avui malgrat els esforços de la comunitat científica. D’entre les partícules candidates, més enllà del model estàndard de física de partícules, destaca la Weakly Interacting Massive Particle (WIMP) com una de les més prometedores. S’estima la seva massa entre pocs GeV i centenars de TeV, encaixant perfectament en l’interval d’energies testejades per a la cerca indirecta de la DM. Els telescopis MAGIC, situats a l’Observatorio del Roque de los Muchachos, a l’illa canària de La Palma, fan cerques indirectes de les WIMP des que van entrar en funcionament. Els objectes observats més comuns amb aquest objectiu són les galàxies nanes esferoïdals (dSphs) satèl·lits de la Via Làctia i el centre galàctic amb el seu halo. En aquesta tesis presento el resultat de les cerques indirectes d’anihilació de WIMPs en tres diferents objectes d’observació (el cúmul globular M15 i les dSphs Draco i Coma Berenices), així com els resultats obtinguts a partir de la combinació de les dades de les dues dSphs estudiades i dues dSphs analitzades prèviament dins de la col·laboració MAGIC. No s’ha trobat cap senyal en qualsevol dels 4 estudis. L’estudi de M15 ha constituït un repte, debut al modest excés de densitat de DM que se suposa hi ha en aquest tipus d’objectes i a les grans incerteses sistemàtiques associades als perfils de dispersió de la velocitat de les estrelles en els seus centres. Per tal d’obtenir una estimació de les sensibilitats que es poden obtenir amb aquest tipus d’anàlisis, s’han considerat quatre diferents perfils de densitat de DM en M15. S’han obtingut límits superiors estadístics sobre la mitjana de la secció eficaç d’anihilació de WIMPs multiplicada per la velocitat (en endavant velocity-averaged cross-section) considerant perfils de densitat de DM proporcionats en els treballs de H.E.S.S. i VERITAS. Els resultats obtinguts són compatibles amb els presentats en les seves respectives publicacions. Addicionalment, s’han trobat límits superior de prova considerant perfils de densitat de M15 i del seu contingut en matèria no bariònica en un escenari d’un cos dominat per DM. Els límits obtinguts amb aquest mètode són millors que els que s’obtenen amb les més prometedores dSphs, però al mateix temps són poc realistes i proporcionen només un valor mínim de la velocity-averaged cross-section que es pot assolir en M15, a l’espera de noves mesures cinemàtiques en les seves parts centrals. Les dSphs Draco i Coma Berenices han estat observades amb els telescopis MAGIC dins d’una campanya de diversificació de fonts d’observació plurianual. S’han obtingut límits superiors realistes amb un 95% de nivell de confiança en la velocity-averaged cross-section de WIMPs. La combinació de les dades d’aquestes dues dSphs amb les de les altres dues anteriorment observades amb MAGIC (Segue 1 i Ursa Major II) ha permés de millorar la sensibilitat en la cerca indirecta d’anihilació de WIMPs. Els resultats obtinguts constitueixen el llegat de la col·laboració MAGIC en aquest camp, i són els més restrictius trobats a MAGIC i els més estrictes en l’interval de massa de WIMP ~10-100 TeV en les cerques en astrofísica de raigs gamma, arribant a límits superiors de l’ordre de 10⁻²⁴ cm³/s sobre la velocity-averaged cross-section amb un nivel de confiança del 95%. En l’última part de la tesis es presenta la meva contribució al desenvolupament i posada a punt del Barcelona Raman LIDAR, un instrument avançat i no comercial optimitzat per a la monitorització de l’atmosfera sobre el Cherenkov Telescope Array.
La naturaleza de la materia oscura (DM) en el universo sigue siendo un enigma a día de hoy a pesar los esfuerzos de la comunidad científica. Entre las partículas candidatas más allá del modelo estándar de física de partículas destaca la Weakly Interacting Massive Particle (WIMP) como una de las más prometedoras. Su masa se estima entre pocos GeV y cientos de TeV, encajando perfectamente en el intervalo de energías testeadas para la búsqueda indirecta de la materia oscura. Los telescopios MAGIC, situados en el Observatorio del Roque de los Muchachos en la isla canaria de La Palma, realizan búsquedas indirectas de WIMP desde que entraron en operación. Los objetos observados más comunes para tal fin son las galaxias esferoidales enanas (dSphs) satélites de la Vía Láctea y el centro galáctico y su halo. En esta tesis presento el resultado de las búsquedas indirectas de aniquilación de WIMPs en tres diferentes objetos de observación (el cúmulo globular M15 y las dSphs Draco y Coma Berenices) así como los resultados obtenidos a partir de la combinación de los datos de las dos dSphs estudiadas y dos dSphs analizadas previamente dentro de la colaboración MAGIC. No se ha encontrado ninguna señal en cualquiera de los 4 estudios. El estudio de M15 ha constituido un reto debido al modesto exceso de densidad de DM supuesto en este tipo de objetos y las grandes incertidumbres asociadas a los perfiles de dispersión de la velocidad de las estrellas en sus centros. Para obtener una estimación de las sensibilidades que se pueden obtener en este tipo de análisis, se han considerado cuatro diferentes perfiles de densidad de DM de M15. Se han obtenido límites superiores estadísticos sobre el promedio de la sección eficaz de aniquilación de WIMPs multiplicada por la velocidad (en adelante velocity-averaged cross-section) considerando los perfiles de densidad de DM proporcionados en los trabajos de H.E.S.S. y VERITAS. Los resultados obtenidos son compatibles con los presentados por sus respectivas publicaciones. Adicionalmente, se han encontrado límites superiores de prueba considerando perfiles de densidad de DM obtenidos a partir de la convolución del perfil de densidad de M15 y de su contenido de materia no bariónica en un escenario de un cuerpo dominado por DM. Los límites obtenidos con este método son mejores que los que se obtienen con las más prometedoras dSphs, pero al mismo tiempo son poco realistas y proporcionan solamente un valor mínimo de la velocity-averaged cross-section alcanzable en M15, a la espera de nuevas medidas cinemáticas en sus partes centrales. Las dSphs Draco y Coma Berenices han sido observadas con los telescopios MAGIC dentro de una campaña de diversificación de fuentes de observación plurianual. Se han obtenido límites superiores realistas con un 95% de nivel de confianza en la velocity-averaged cross-section de WIMPs. La combinación de los datos de estas dos dSphs con los de las otras dos dSphs anteriormente observadas con MAGIC (Segue 1 y Ursa Major II) ha permitido mejorar la sensibilidad en la búsqueda indirecta de aniquilación de WIMPs. Los resultados obtenidos constituyen el legado de la colaboración MAGIC en este campo, y son los más restrictivos alcanzados en MAGIC y los más estrictos en el intervalo de masa de WIMP ~10-100 TeV en las búsquedas en astrofísica de rayos gamma, llegando a límites superiores del orden de 10⁻²⁴ cm³/s sobre la velocity-averaged cross-section con un nivel de confianza del 95%. En la última parte de la tesis se presenta mi contribución al desarrollo y puesta a punto del Barcelona Raman LIDAR, un instrumento avanzado y no comercial optimizado para la monitorización de la atmósfera encima del Cherenkov Telescope Array.
The nature of Dark Matter (DM) in the Universe is still an enigma at present day, despite the efforts of the scientific community. Among the favorite DM particle candidates beyond the Standard Model of particle physics, the Weakly Interacting Massive Particle (WIMP) is of the most promising. Predicted to have a mass between few GeV and hundreds of TeV, it fits perfectly in the energy range tested by indirect dark matter searches with Imaging Atmospheric Cherenkov Telescopes. The MAGIC telescopes, located at the Observatorio del Roque de los Muchachos, on the Canary Island of La Palma, perform indirect DM searches for WIMPs since their very beginning. Among the targets observed, dwarf spheroidal satellite galaxies (dSphs) and the Galactic Center and halo are the most common, both expected to be embedded in a high DM overdensity. In this thesis I present the outcome of indirect WIMP annihilation searches from three different observation targets (the globular cluster M15 and the dSphs Draco and Coma Berenices) together with the results obtained by a combination of data from the two dSphs studied in this thesis and two dSphs previously analyzed by the MAGIC collaboration. No signal has been observed in any of the four searches. The study of M15 has been a challenge due to its relatively low DM overdensity predicted and the large systematic uncertainties resulting from the current lack of star velocity dispersion profiles at its core. In order to get an estimate of the sensitivities achievable with this type of analyses, four different realizations of the M15 DM density profile were investigated. Statistical upper limits on the velocity-averaged WIMP annihilation cross-section have been obtained with the use of the DM profiles provided by the H.E.S.S. and VERITAS experiments. The results obtained are compatible with those presented in their respective publications. Further toy statistical upper limits have been obtained taking into account DM density profiles from a convolution of the M15 density profile and its expected non-baryonic matter content in a scenario of DM domination. The limits retrieved with this method are better than the most promising ones from dSphs, but at the same time systematically unreliable, and provide only a minimum value of the velocity-averaged cross-section attainable in M15, awaiting for new kinematic measurements at globular clusters cores. The dSphs Draco and Coma Berenices were observed during the past years with the MAGIC telescopes within a multi-year diversification campaign. Reliable 95% CL upper limits on the velocity-averaged WIMP annihilation cross-section have been retrieved and are presented in this thesis. The data of these two dSphs are also combined with the ones of the two other dSphs previously observed with the MAGIC telescopes, namely Segue 1 and Ursa Major II, to achieve the best sensitivity for indirect WIMP DM annihilation searches. The results obtained constitute the MAGIC collaboration legacy in this field, and are the most constraining reached by MAGIC and the most stringent in the ~ 10-100 TeV WIMP DM mass interval in gamma-ray astrophysics searches so far, reaching upper limits of the order of 10⁻²⁴ cm³/s for the velocity-averaged cross-section. In the last part of this thesis, I present my contribution to the development and set up of the Barcelona Raman LIDAR, an advanced and no commercial instrument optimized for the atmospheric monitoring above the future Cherenkov Telescope Array.
Universitat Autònoma de Barcelona. Programa de Doctorat en Física

Erste Anzeichen für die Existenz von Dunkler Materie wurden 1933 entdeckt. Der Astrophysiker Fritz Zwicky beobachtete die Geschwindigkeitsverteilung im Coma Cluster und fand dabei heraus, dass 400 mal mehr Materie im Galaxie Haufen sein muss, damit dieser gravitativ gebunden sein kann oder der Galaxie Haufen würde sich aufösen. Trotz erheblicher Bemühungen über die letzten 80 Jahre ist nicht viel über Dunkle Materie bekannt. Das einzige was man weiÿ ist, dass Dunkle Materie gravitativ aber nicht elektromagnetisch wechselwirkt und Dunkle Materie stellt den gröÿten Bestandteil der Materie im Universum da. Doch derzeitige Experimente die nach Dunkler Materie suchen, sowohl direkte Suchen als auch indirekte, beginnen sensitiv genug zu werden um interessante Parameterbereiche von Dunkle Materie Kandidaten zu untersuchen wie das leichteste Super-symmetrische Teilchen, was bedeutet, dass die Entdeckung von Dunkler Materie in der nahen Zukunft sein könnte. In dieser Arbeit wird eine Signalsummierung von H.E.S.S. Zwerg Galaxien Daten durchgeführt und obere Ausschlussgrenzen berechnet. Weiterhin wird die Leistung einer Dunklen Materie Suche im galaktischen Zentrum durch CTA präsentiert für verschiedene mögliche Teleskop Anordnungen und verschiedene Annihilation Kanäle. Die Ergebnisse werden zeigen, dass CTA in der Lage sein wird geschwindigkeitsgemittelte Annihilations Wirkungsquerschnitte von 3 * 10^-26 cm^3s^1 und geringer, der geschwindigkeitsgemittelte Annihilations Wirkungsquerschnitt der für schwach wechselwirkende Dunkle Materie erwartet wird, in 100 h zu erreichen. Diese Beobachtungszeit kann innerhalb von ein bis zwei Jahren erreicht werden.
First indications for the existence of Dark Matter appeared in 1933. The astrophysicist Fritz Zwicky observed the velocity dispersion of the Coma Cluster and found out that 400 times the visible mass must be contained in the galaxy cluster or the cluster could not be gravitationally bound and would disperse.Despite extensive efforts over the last 80 years not much is known about Dark Matter. The facts known are that Dark Matter interacts via gravitation, does not interact electromagneticly and is the main constituent of matter. But current experiment searching for Dark Matter directly and indirectly begin to reach sensitivities that can probe interesting parameter spaces for Dark Matter candidates like the lightest supersymmetric particle, meaning the first Dark Matter detections could happen in the near future.In this thesis a dwarf stacking analysis for Dark Matter signal search using H.E.S.S. data is performed and a upper limit is calculated. Furthermore the prospect for a Dark Matter search with CTA in the galactic center region of the Milky Way is presented for different candidate arrays and different annihilation channels. The results will show that CTA will be able to reach velocity annihilation below 3 *10^-26 cm^3s^-1, the velocity annihilation crosssection expected for a weakly interacting Dark Matter particle, within 100 h of observation which can reasonably be acquired within one to two years.

Gamma-ray astronomy is generally viewed as an adjunct to cosmic ray physics. As such, the observation of very high energy gamma-rays will allow a new and complementary means of examining the origin and evolution of cosmic rays. However, at present the atmospheric Cerenkov technique (the technique by which very high energy gamma-rays are observed) is seriously hampered by limited flux sensitivity. Monte Carlo simulations suggest that the application of imaging to the atmospheric Cerenkov technique will provide a much needed increase in sensitivity. The successful application of imaging to very high energy gamma-ray observations of the Crab nebula will be discussed, as will improved techniques for calibration and noise rejection. These observations permit an improved estimate of the nebular magnetic field strength.

The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is a ground based gamma-ray telescope. An array of mirrors allow the detection of an astronomical Cherenkov light signal in an large background light flux. This background flux need to be carefully characterized in order to eliminate its contribution and recover the precious Cherenkov signal. This thesis describes an instrument to study the photon flux from the night sky in the wavelength region relevant for the atmospheric Cherenkov telescopes. The integral photon flux as well as its wavelength dependence can be measured by a baffled tube defining a solid angle viewed by a photomultiplier tube.

We carried out a three year (2013-2015) observational campaign at the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile in which we obtained ~1000 astronomical images in the field of 11 Galactic globular clusters. The selection of these stellar systems was focused mainly on the visibility of the targets and their relevant physical properties available in the catalogues, among them were considered the density, variable stars known, colour-magnitude diagrams, and luminosity. The telescope was equipped with an electron-multiplying CCD (EMCCD) with the aim of taking very short exposure-time images. The camera was configured to take 10 frames per second. Due to this, the brighter stars observed were not affected by saturation, it helped to give higher signal to noise ratio to the fainter stars and, importantly, it minimised the effects of the atmospheric turbulence such as blending between stars in the crowded fields. To produce normal-exposure-time images (minutes) we implemented the shift-and-add technique that also enabled us to produce images with better angular resolution than previously achieved with conventional CCDs on ground-based telescopes, and even enabled us to produce images with angular resolution close to that obtained with space telescopes. The detection of the stars in each of the globular clusters and the photometry was performed via difference image analysis by using the DanDIA pipeline whose procedures and mathematical techniques have been demonstrated to produce high-precision time-series photometry of very crowded stellar regions. We produced time-series photometry for ~15000 stars in the fields observed which were statistically analysed in order to automatically extract variable stars. Our aim is to complete, or improve, the census of the variable star population in the globular clusters. In NGC 6715, we found light curves for 17 previously known variable stars near the edges of our reference image (16 RR Lyrae and 1 semi-regular) and we discovered 67 new variables (30 RR Lyrae, 21 long-period irregular, 3 semi-regular, 1 W Virginis, 1 eclipsing binary, and 11 unclassified). This cluster was particularly interesting because apart from the results obtained, it shows the benefits of using the EMCCD cameras and the shift-and-add technique. It is a cluster studied several times including data obtained with the OGLE survey and also with the Hubble Space Telescope and our discoveries were still new. Our new RR Lyrae star discoveries help confirm that NGC 6715 is of intermediate Oosterhoff type. In the other 10 globular clusters, we obtained light curves for 31 previously known variable stars (3 L, 2 SR, 20 RR Lyrae, 1 SX Phe, 3 cataclysmic variables, 1 EW and 1 NC) and we discovered 30 new variables (16 L, 7 SR, 4 RR Lyrae, 1 SX Phe and 2 NC). In NGC 6093, we analysed the famous case of the 1860 Nova, for which no observations of the Nova in outburst have been made until the present study. Ephemerides and photometric measurements for the variable stars are available in electronic form through the Strasbourg Astronomical Data Centre.

The degradation of astronomical images caused by atmospheric turbulence will be much more severe in the next generation of terrestrial telescopes and its compensation will require deformable mirrors with up to tens-of-thousands of actuators.

Current designs for these correctors consist of scaling up the proven technologies of flexible optical plates deformed under the out-of-plane action of linear actuators. This approach will lead to an exponential growth of cost with the number of actuators, and in very complex mechanisms.

This thesis proposes a new concept of optical correction which is modular, robust, lightweight and low-cost and is based on the bimorph in-plane actuation.

The adaptive mirror consists of segmented identical hexagonal bimorph mirrors allowing to indefinitely increase the degree of correction while maintaining the first mechanical resonance at the level of a single segment and showing an increase in price only proportional to the number of segments.

Each bimorph segment can be mass-produced by simply screen-printing an array of thin piezoelectric patches onto a silicon wafer resulting in very compact and lightweight modules

and at a price essentially independent from the number of actuators.

The controlled deformation of a screen-printed bimorph mirror was experimentally achieved with meaningful optical shapes and appropriate amplitudes; its capability for compensating turbulence was evaluated numerically. The generation of continuous surfaces

by an assembly of these mirrors was numerically simulated and a demonstrator of concept consisting of 3 segments was constructed.
Doctorat en Sciences de l'ingénieur
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