Focal plane wavefront sensing on SUBARU/SCExAO

Focal plane wavefront sensing is an elegant solution for wavefront sensing since near-focal images of any source taken by a detector show distortions in the presence of aberrations. Non-Common Path Aberrations and the Low Wind Effect both have the ability to limit the achievable contrast of the finest coronagraphs coupled with the best extreme adaptive optics systems. To correct for these aberrations, the Subaru Coronagraphic Extreme Adaptive Optics instrument hosts many focal plane wavefront sensors using detectors as close to the science detector as possible. We present seven of them and compare their implementation and efficiency on SCExAO. This work will be critical for wavefront sensing on next generation of extremely large telescopes that might present similar limitations

Etude théorique et expérimentale d'un laser à solide de forte puissance moyenne, déclenché à haute-cadence et possédant une bonne qualité de faisceau

Le but de ce travail est de concevoir, étudier, comprendre et optimiser un laser à solide déclenché à haute-cadence (7 à 10 kHz), alliant forte puissance moyenne (500 W) et bonne qualité de faisceau (M <10), utilisé dans une source extrême-ultraviolette à 13,5 nm pour la nanolithographie.Dans ces lasers, le fort pompage induit des effets thermiques qui dégradent considérablement les performances (rendement, qualité de faisceau) du laser. Il s agit principalement d un effet de lentille thermique aberrante qui perturbe la stabilité des cavités.Dans ce travail, les focales thermiques et l aberration sphérique sont quantifiées précisément, expérimentalement d une part, puis par des calculs théoriques. Les deux études montrent une très bonne concordance et permettent de mettre en évidence l importance du profil de pompage, de la dépendance en température de la conductivité thermique et du dn/dT du cristal laser dans l amplitude de ces effets. On montre également que la position du barreau dans la cavité a une influence notable.Les conséquences de la focale thermique et de l aberration sphérique sur les performances du laser sont également étudiées, par de petits calculs simples et par simulation informatique. Ces méthodes permettent de prévoir avec une bonne précision les performances énergétiques du laser, de même que le M du faisceau, mais seulement dans le cas d un barreau non aberrant.Finalement, il est possible de concevoir des dispositifs compensateurs, à insérer dans la cavité laser. Ces dispositifs sont très efficaces sur les cavités de faible M , et permettent d obtenir une amélioration importante de la brillance des sources.The aim of this work is to design, study, understand and optimize a high-repetition-rate (7 to 10 kHz) solid-state laser, with at the same time high power (500 W) and good beam quality (M <10), used in an extreme-UV source ( at 13,5 nm) for nanolithography.In this kind of lasers, high pumping power leads to thermal effects which lower the performances (efficiency, beam quality) of the laser. It is to say, mainly, an aberrant thermal lensing effect influencing the stability of the resonator.In this work, thermal focal length and spherical aberration are precisely quantified, experimentally and then theoretically. Both studies show a very good match and allow to show the importance of the pumping profile, and of the dependence with temperature of thermal conductivity and dn/dT of the laser crystal in the amplitude of these effects. It is also proven that the position of the laser rod inside the cavity has a significant influence.The consequences of the thermal lens and the spherical aberration are also studied, with simple calculations and simulations with the software Commod Pro. Thanks to these methods, energetic performances of the laser can be predicted with good precision, as well as the M of the beam, but only in the case of a non aberrating rod.Eventually, thanks to these preliminary studies, compensating devices can be designed, made of phase-plate or a combination of simple lenses and put inside the cavity. Theses devices are very efficient on cavity with a low M , and thanks to them, sources with high brightness can be obtained.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Alignement et cophasage en temps-réel de systèmes multi-pupilles avec des détecteurs en plan focal sur un object non résolu

International audienceThe alignment of the subapertures is a major challenge for future segmented telescopes and telescope arrays. We show here that a focal plane wave-front sensor using only two images can fully and efficiently align a multiple aperture system, both for the alignment (large amplitude tip/tilt aberrations correction) and phasing (piston and small amplitude tip/tilt aberrations correction) modes. We derive a new algorithm for the alignment of the subapertures : ELASTICS. We quantify the novel algorithm performance by numerical simulations. We show that the residues are within the capture range of the fine algorithms. We also study the performance of LAPD, a recent real-time algorithm for the phasing of the sub-apertures. The closed-loop alignement of a 6 sub-aperture mirror provides experimental demonstration for both algorithms.L'alignement des sous-pupilles est une défi majeur pour les futurs télescopes segmentés ou réseaux de télescopes. Nous montrons ici qu'un analyseur de surface d'onde en plan focal n'utilisant que deux images peut corriger un système multi-pupille de manière complète et efficace, aussi bien pour l'alignement initial (correction des basculements de grande amplitude) que le cophasage (correction des perturbations de piston et basculement de petite amplitude). Nous établissons un nouvel algorithme (ELASTICS) pour l'alignement des sous-pupilles, dont nous quantifions les performances par simulation numérique et montrons que les résidus sont inclus dans la zone d'accrochage des algorithmes fins. Nous étudions aussi les performances de LAPD, a algorithme temps-réel récent pour le cophasage des sous-pupilles. Une validation expérimentale de ces deux algorithmes a été effectuée par l'alignement en boucle fermée d'un miroir à 6 sous-pupilles

Turbulent and adaptive optics corrected point-spread functions as convolutive orders of the phase power spectral density

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Adaptive optics pre-compensation for GEO feeder links: Towards an experimental demonstration

International audienceHigh throughput ground to GEO satellite telecommunication systems will require very capacitive links for the uplink. When diffraction limited, a few optical Watts per channel are sufficient to close the link budget. In the presence of atmospheric turbulence, higher emission powers are necessary to cope with the subsequent disruptions of the beam. Pre-compensation by adaptive optics has been identified as a key strategy to keep the requested power at reasonable levels. However its performance is limited by point-ahead anisoplanatism. Fine trade-offs shall be carried out to overcome this limitation while considering the specificities of optical telecommunication requirements (low fading probably, short fading duration, manageable cost and complexity). The expected performance of the pre-compensation by adaptive optics for optical feeder links is investigated through numerical simulations. A ground-to-ground experimental demonstration is proposed. The selected slant line of sight and the beam geometry is shown to induce turbulence effects, including angular decorrelation, that are representative of the GEO feeder link scenario when considering an appropriate setup

Analysis of satellite-to-ground quantum key distribution with adaptive optics

Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution (QKD), with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations

Amélioration du taux de clé secrète QKD satellite-sol avec l'optique adaptative

International audienceWe demonstrate the gain brought by adaptive optics for space-ground QKD links. Refined modeling of turbulence, adaptive optics and QKD, including finite-size effects, shows improvement by several orders of magnitude of the secret key rate.Nous démontrons le gain apporté par l'optique adaptative pour les liaisons QKD espace-sol. Une modélisation raffinée de la turbulence, de l'optique adaptative et du QKD, incluant les effets de taille finie, montre une amélioration de plusieurs ordres de grandeur du taux de clé secrète

Analysis of satellite-to-ground quantum key distribution with adaptive optics

International audienceFuture quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution (QKD), with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations

Analysis of satellite-to-ground quantum key distribution with adaptive optics

Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution (QKD), with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations

Amélioration du taux de clé secrète QKD satellite-sol avec l'optique adaptative

International audienceWe demonstrate the gain brought by adaptive optics for space-ground QKD links. Refined modeling of turbulence, adaptive optics and QKD, including finite-size effects, shows improvement by several orders of magnitude of the secret key rate.Nous démontrons le gain apporté par l'optique adaptative pour les liaisons QKD espace-sol. Une modélisation raffinée de la turbulence, de l'optique adaptative et du QKD, incluant les effets de taille finie, montre une amélioration de plusieurs ordres de grandeur du taux de clé secrète