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

Tip tilt and focus estimation based on LGS and downlink joint measurements for ground to GEO satellite optical communication link

Achieving high data rates in GEO Feeder optical uplinks faces challenges due to the fading nature of the channel induced by atmospheric turbulence. Adaptive optics pre-compensation using downlink measurements is a solution to mitigate the impact of the turbulence. However, the point-ahead angle anisoplanatism, inherent to the bidirectional link geometry, limits the uplink correction efficiency, leading to persistent signal fades and loss of information onboard the satellite. We recently proposed a new minimum mean square error method that improves the phase estimation at the PAA based on the downlink phase and log amplitude measurements, reducing the anisoplanatism impact on the coupled flux. Alternatively, a laser guide star can be used to measure the phase at the PAA. However, it is currently challenging to retrieve the tip, tilt, and focus modes, whose correction is essential to improve the link quality. In this article, we propose to combine both techniques to estimate the tip, tilt, and focus at the PAA by incorporating the LGS high-order measurements in the MMSE formalism. We develop the associated analytical reconstructor and evaluate the performance of the phase estimation and the gain on the coupled flux statistics aboard the GEO satellite, considering an idealized LGS system. The new estimator is shown to reduce the tip, tilt, and focus error variances by up to 70% of their initial value

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

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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

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

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

Ophtalmoscope plein champ assisté par Optique Adaptative avec boucle d’asservissement à haute cadence et capacité de projeter des motifs d’illumination

International audienceThe design and performance of an adaptive optics flood illumination ophthalmoscope (AO-FIO) platform, based on eye motion and dynamic aberrations experimental analysis, are described. The system incorporates a custom-built real-time controller, enabling up to 70 Hz loop rate without jitter, and an AO-corrected illumination capable of projecting high-resolution features in the retina. Wide-field (2.7°×5.4°) and distortionless images from vessel walls, capillaries, and the lamina cribrosa are obtained with an enhanced contrast and signal-to-noise ratio, thanks to careful control of AO parameters. The high spatial and temporal resolution (image acquisition up to 200 Hz) performance achieved by this platform enables the visualization of vessel deformation and blood flow. This system opens up the prospect of a return to favor of flood illumination adaptive optics systems provided that its high pixel rate and structured illumination capabilities are exploited.La conception et la performance de l’ophtalmoscope plein champ assisté par Optique Adaptative (OA), basés sur des analyses expérimentales des mouvements et aberrations oculaires, sont décrites. Le système est composé d’un calculateur en temps-réel qui permet d’atteindre une vitesse de boucle d’asservissement de 70Hz. Le système permet aussi la projection de motifs dans la rétine. Grâce au contrôle et la maîtrise d’un système d’Optique Adaptative, des images à grand champ (2.7x5.4°) sans distorsion des différentes régions de la rétine présentent une amélioration de contraste et de rapport signal sur bruit. La haute résolution spatio-temporelle permet également la visualisation des déformations vasculaire et du flux sanguin. Ce système ouvre des nouvelles perspectives en ophtalmoscopie plein-champ, qui pourrait s'imposer dans les années à venir à condition que sa haute résolution temporelle et sa capacité de projeter des motifs d’illumination soient exploitées