Ophthalmic instrumentation equipped with adaptive optics offers the possibility of rapid and automated correction of the eye's optics for improving vision and for improving images of the retina. One factor that limits the widespread implementation of adaptive optics is the cost of the wave-front corrector, such as a deformable mirror. In addition, the large apertures of these elements require high pupil magnification, and hence the systems tend to be physically large. We present what are believed to be the first closed-loop results when a compact, low-cost, surface micromachined, microelectromechanical mirror is used in a vision adaptive-optics system. The correction performance of the mirror is shown to be comparable to that of a Xinetics mirror for a 4.6-mm pupil size. Furthermore, for a pupil diameter of 6.0-mm, the residual rms error is reduced from 0.36 to 0.12 microm and individual photoreceptors are resolved at a pupil eccentricity of 1 degrees from the fovea.

Argon ion machining of released thin-film devices is shown to alter the contour shape of free-standing thin-film structures by affecting their through-thickness stress distributions. In experiments conduffcted on MEMS thin-film mirrors it is demonstrated that post-release out-of-plane deformation of such structures can be reduced using this ion beam machining method. In doing so optically flat surfaces (curvature 0.001 mm 1) are achieved on a number of 3 m-thick surface micromachined silicon structures, including mirrors with either initially positive curvature or initially negative curvature measuring up to 0.02 mm 1. An analytical model incorporating the relevant mechanics of the problem is formulated and used to provide an understanding of the mechanisms behind the planarization process based on ion machining. The principal mechanisms identified are 1) amorphization of a thin surface layer due to ion beam exposure and 2) gradual removal of stressed material by continued exposure to the ion beam. Curvature history predictions based on these mechanisms compare well with experimental observations. [670]

We report on the development of a new MEMS deformable mirror (DM) system for the hyper-contrast visible nulling coronagraph architecture designed by the Jet Propulsion Laboratory for NASA's Terrestrial Planet Finding (TPF) mission. The new DM is based largely upon existing lightweight, low power MEMS DM technology at Boston University (BU), tailored to the rigorous optical and mechanical requirements of the nulling coronagraph. It consists of 329-hexagonal segments on a 600Ι m pitch, each with tip/tilt and piston degrees of freedom. The mirror segments have 1Ι m of stroke, a tip/tilt range of 600 arc-seconds, and maintain their figure to within 2nm RMS under actuation. The polished polycrystalline silicon mirror segments have a surface roughness of 5nm RMS and an average curvature of 270mm. Designing a mirror segment that maintains its figure during actuation was a very significant challenge faced during DM development. Two design concepts were pursued in parallel to address this challenge. The first design uses a thick, epitaxial grown polysilicon mirror layer to add rigidity to the mirror segment. The second design reduces mirror surface bending by decoupling actuator diaphragm motion from the mirror surface motion. This is done using flexure cuts around the mirror post in the actuator diaphragm. Both DM architectures and their polysilicon microfabrication process are presented. Recent optical and electromechanical characterization results will also be discussed, in addition to plans for further improvement of DM figure to satisfy nulling coronagraph optical requirements.

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Abstract. We report on the development of microelectromechanical (MEMS) deformable mirrors designed for ground and space-based astronomical instruments using adaptive optics. These light-weight, low power deformable mirrors will have an active aperture of up to 25.2mm consisting of thin silicon membrane mirror supported by an array of up to 4096 electrostatic actuators exhibiting no hysteresis and sub-nanometer repeatability. The continuous membrane deformable mirrors, coated with a highly reflective metal film, are capable of up to 4µm of stroke, have a surface finish of <10nm RMS with a fill factor of 99.8%. The segmented device has a range of motion of 1um of piston and 600 arc-seconds of tip/tilt simultaneously and a surface finish of 5nm RMS. Presented in this paper are device characteristics and performance results for these devices. Motivation for high-resolution wavefront correctionMost large ground based telescopes now employ AO as an essential and enabling tool for highresolution imaging. Though recent progress in AO for current and future large telescopes has been technologically exciting, its impact on astronomical science remains modest to date. AO technology is still inadequate to compensate for the larger wavefront errors and shorter atmospheric coherence lengths associated with visible wavelength observation. Its simplest implementation allows only a narrow field of compensation, and more ambitious instrument concepts are limited by the cost, size, and complexity of AO components, especially the DM. A critical assessment of AO technology was funded by the National Science Foundation several years ago, resulting in a 2008 report entitled A Roadmap for the Development of United States Astronomical Adaptive Optics. The roadmap identifies single major goal for wavefront correction: "Development of scalable, cost-effective DM technologies" and recommends a high-priority research investment to achieve this goal: "High stroke, high actuator count [deformable] mirrors to enable correction at high spatial frequencies over narrower fields of view."The coming generation of ELTs, will be the first to be designed with AO at the outset. Since the benefits of AO increase nonlinearly with telescope aperture, a phenomenon sometimes called D 4 scaling, AO will be essential for many ELT science goals [1,2]. Promising AO instruments that will require new DMs include multi-conjugate adaptive optics (MCAO), multi-object adaptive optics (MOAO), and extreme adaptive optics (ExAO) [3]. MCAO employs two or more guide stars to enable tomographic wavefront error sensing, and then two or more deformable mirrors in series to correct those errors. The result is a wider corrected field of view [4]. This technique was recently used to produce the sharpest whole-planet (Jupiter) picture ever taken from the ground [5]. MOAO is an instrument concept that also uses multiple guide stars and multiple deformable mirrors [6]. However in MOAO, many DMs would be used in parallel to apply independent corrections for the turbulence-induce...