Optimized actuators for ultrathin deformable primary mirrors

A novel design and selection scheme for surface-parallel actuators for ultrathin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented

Optimization of Electrode Configuration in Surface-Parallel Actuated Deformable Mirrors

Thin, lightweight and low-cost deformable mirrors have been recently proposed, providing a pertinent device for wavefront error correction. We present different approaches to optimize actuator arrangement. The design is optimized according to a given correction requirement, through the number of electrodes, their shape and location. A first method focuses on the compensation of a given optical aberration (astigmatism). A second method directly optimizes the correction of a set of optical modes, taking into account the voltage limitation. We will describe the optimization techniques and give some examples of applications and design performance

Miroirs actifs de l'espace - Développement de systèmes d'optique active pour les futurs grands observatoires

The need for both high quality images and light structures is one of the main driver in the conception of space telescopes. An e fficient wave-front control will then become mandatory in the future large observatories, ensuring the optical performance while relaxing the specifications on the global system stability. Consisting in controlling the mirror deformation, active optics techniques can be used to compensate for primary mirror deformation, to allow the use of reconfigurable instruments or to manufacture aspherical mirror with stress polishing. In this manuscript, the conception of active mirrors dedicated to space instrumentation is presented. Firstly, a system compensating for large lightweight mirror deformation in space, is designed and its performance are experimentally demonstrated. With 24 actuators, the MADRAS mirror (Mirror Actively Deformed and Regulated for Applications in Space) will perform an effi cient wave-front correction in the telescope's pupil relay. Secondly, a warping harness for the stress polishing of the 39 m European Extremely Large Telescope segments is presented. The performance of the process is predicted and optimized with Finite Element Analysis and the segments mass production is considered. Thirdly, two original concepts of deformable mirrors with a minimum number of actuators have been developed. The Variable Off -Axis parabola (VOALA) is a 3-actuators system and the Correcting Optimized Mirror with a Single Actuator (COMSA) is a 1-actuator system. The active systems presented in this manuscript off er many advantages for the future large space-borne observatories: limited number of degrees of freedom, compactness, low weight, robustness and reliability. They will allow some technological breakthroughs and lead to innovative telescope architectures.Le besoin tant en haute qualité d'imagerie qu'en structures légères est l'un des principaux moteurs pour la conception des télescopes spatiaux. Un contrôle e fficace du front d'onde va donc devenir indispensable dans les futurs grands observatoires spatiaux, assurant une bonne performance optique tout en relâchant les contraintes sur la stabilité globale du système. L'optique active consiste à contrôler la déformation des miroirs, cette technique peut être utilisée afin de compenser la déformation des grands miroirs primaires, afin de permettre l'utilisation d'instrument reconfigurable ou afin de fabriquer des miroirs asphériques avec le polissage sous contraintes. Dans ce manuscrit, la conception de miroirs actifs dédiés à l'instrumentation spatiale est présentée. Premièrement, un système compensant la déformation d'un grand miroir allégé dans l'espace est conçu et ses performances sont démontrées expérimentalement. Avec 24 actionneurs, le miroir MADRAS (Miroir Actif Déformable et Régulé pour Applications Spatiales) e ffectuera une correction e fficace du front d'onde dans un relais de pupille du télescope. Deuxièmement, un harnais de déformation pour le polissage sous contraintes des segments du télescope géant européen de 39 m (E-ELT) est présenté. La performance du procédé est prédite et optimisée avec des analyses éléments finis et la production en masse des segments est considérée. Troisièmement, deux concepts originaux de miroirs déformables avec un nombre minimal d'actionneurs ont été développés. VOALA (Variable O ff-Axis parabola) est un système à trois actionneurs et COMSA (Correcting Optimized Mirror with a Single Actuator) est un système à un actionneur. Les systèmes actifs présentés dans ce manuscrit off rent de nombreux avantages pour une utilisation dans les futurs grands observatoires spatiaux: nombre de degrés de liberté limités, compacité, légèreté, robustesse et fiabilité. Ils permettront d'importantes ruptures technologiques et l'apparition d'architectures de télescope innovantes

Stress polishing demonstrator for ELT M1 segments and industrialisation

After two years of research and development under ESO support, LAM and Thales SESO present the results of their experiment for the fast and accurate polishing under stress of ELT 1.5 meter segments as well as the industrialization approach for mass production. Based on stress polishing, this manufacturing method requires the conception of a warping harness able to generate extremely accurate bending of the optical surface of the segments during the polishing. The conception of the warping harness is based on finite element analysis and allowed a fine tuning of each geometrical parameter of the system in order to fit an error budget of 25nm RMS over 300μm of bending peak to valley. The optimisation approach uses the simulated influence functions to extract the system eigenmodes and characterise the performance. The same approach is used for the full characterisation of the system itself. The warping harness has been manufactured, integrated and assembled with the Zerodur 1.5 meter segment on the LAM 2.5meter POLARIS polishing facility. The experiment consists in a cross check of optical and mechanical measurements of the mirrors bending in order to develop a blind process, ie to bypass the optical measurement during the final industrial process. This article describes the optical and mechanical measurements, the influence functions and eigenmodes of the system and the full performance characterisation of the warping harness

Space active mirrors : Active optics developments for future large observatories

Le besoin tant en haute qualité d'imagerie qu'en structures légères est l'un des principaux moteurs pour la conception des télescopes spatiaux. Un contrôle efficace du front d'onde va donc devenir indispensable dans les futurs grands observatoires spatiaux, assurant une bonne performance optique tout en relâchant les contraintes sur la stabilité globale du système. L'optique active consiste à contrôler la déformation des miroirs, cette technique peut être utilisée afin de compenser la déformation des grands miroirs primaires, afin de permettre l'utilisation d'instrument reconfigurable ou afin de fabriquer des miroirs asphériques avec le polissage sous contraintes. Dans ce manuscrit, la conception de miroirs actifs dédiés à l'instrumentation spatiale est présentée. Premièrement, un système compensant la déformation d'un grand miroir allégé dans l'espace est conçu et ses performances sont démontrées expérimentalement. Avec 24 actionneurs, le miroir MADRAS (Miroir Actif Déformable et Régulé pour Applications Spatiales) effectuera une correction efficace du front d'onde dans un relais de pupille du télescope. Deuxièmement, un harnais de déformation pour le polissage sous contraintes des segments du télescope géant européen de 39 m (E-ELT) est présenté. La performance du procédé est prédite et optimisée avec des analyses éléments finis et la production en masse des segments est considérée. Troisièmement, deux concepts originaux de miroirs déformables avec un nombre minimal d'actionneurs ont été développés. VOALA (Variable Off-Axis parabola) est un système à trois actionneurs et COMSA (Correcting Optimized Mirror with a Single Actuator) est un système à un actionneur.The need for both high quality images and light structures is one of the main driver in the conception of space telescopes. An efficient wave-front control will then become mandatory in the future large observatories, ensuring the optical performance while relaxing the specifications on the global system stability. Consisting in controlling the mirror deformation, active optics techniques can be used to compensate for primary mirror deformation, to allow the use of reconfigurable instruments or to manufacture aspherical mirror with stress polishing. In this manuscript, the conception of active mirrors dedicated to space instrumentation is presented. Firstly, a system compensating for large lightweight mirror deformation in space, is designed and its performance are experimentally demonstrated. With 24 actuators, the MADRAS mirror (Mirror Actively Deformed and Regulated for Applications in Space) will perform an efficient wave-front correction in the telescope's pupil relay. Secondly, a warping harness for the stress polishing of the 39 m European Extremely Large Telescope segments is presented. The performance of the process is predicted and optimized with Finite Element Analysis and the segments mass production is considered. Thirdly, two original concepts of deformable mirrors with a minimum number of actuators have been developed. The Variable Off-Axis parabola (VOALA) is a 3-actuators system and the Correcting Optimized Mirror with a Single Actuator (COMSA) is a 1-actuator system

Visualization_2.tif

AO-SLO image recorded at the fovea of volunteer V1, with a 4°x4° FoV. Two DMs were used for the AO correction

Visualization_3.tif

AO-SLO image of the fovea of volunteer V3, with a 10°x10° FoV. Nine images recorded with a 4°x4° FoV were stitched together

Visualization_1.tif

AO-SLO image recorded at the fovea of volunteer V1, with a 4°x4° FoV. One DM was used for the AO correction