We introduce current status of the feasibility study on a wide field of regard (FoR) Multi-Object Adaptive Optics (MOAO) system for TMT (TMT-AGE: TMT-Analyzer for Galaxies in the Early universe). MOAO is a system which realize high spatial-resolution observations of multiple objects scattered in a wide FoR. In this study, we put emphasise on the FoR as wide as 10′ diameter. The wide FoR is crucial to effectively observe very high-redshift galaxies, which have low surface number density. Simulations of an MOAO system with 8 LGSs show close-to-diffraction-limited correction can be achieved within 5′ diameter FoR and moderate AO correction can be achieved within 10′ diameter FoR. We discuss overall system design of the wide FoR MOAO system considering the constraint from the stroke of small-size deformable mirror (DM). We also introduce current status of developments of key components of an MOAO system; high-dynamic range wavefront sensor (WFS) and large-stroke small-size DM, and real time computer (RTC) with fast tomographic reconstruction.
We propose, design and fabricate here an electrostatically actuated continuous single-crystal-silicon membrane deformable mirror (DM) for astronomical observation. To get a large stroke, a bimorph spring array is used to generate a large air gap between the mirror membrane and the electrode. A DM with a 1.8mm×1.8mm mirror membrane are fabricated by combining Au-Si eutectic wafer bonding and the subsequent all-dry release process. The stroke of the DM is 3.5μm at 115V. The influence function on the nearest neighbor is 51%. The fill factor of the DM is 99.9%.
We are conducting AO development activities in Tohoku university targeting Multi-Object Adaptive Optics (MOAO) system for the next generation ground-based large telescopes. In order to evaluate the accuracy of the tomographic estimation, which is a key of an MOAO system, we assembled a test optical bench to simulate an MOAO system in our optical lab. The system consists with 1) four light sources with single-mode fibers simulating three guide stars and one target object, 2) multiple phase plates simulating atmospheric turbulence structure, and 3) 4 Shack-Hartmann wavefront sensors. Wavefront data from the sensors are reduced with the tomographic algorithm. The evaluation of the accuracy of the tomographic wavefront reconstruction is underway. Additionally, evaluation of an open-loop control of an AO system is underway using an independent module. Once the accuracy of the open-loop control is established, the module will be installed in the tomography test bench and the entire system will be evaluated as an MOAO system. In parallel, we are conducting a development of a large stroke (20μm) Micro Electro Mechanical Systems (MEMS) deformable mirror with large number of elements (<3000). Current status of the development is described.
We started adaptive optics (AO) development activities in Tohoku university targeting Multi-Object Adaptive
Optics (MOAO) system for the next generation ground-based large telescopes. In order to realize an MOAO
system, we are currently conducting two R&Ds. First one is a development of a large stroke (20μm) Micro Electro
Mechanical Systems (MEMS) deformable mirror with large number of elements (>3000) which is necessary to
achieve mild Strehl Ratio in an AO systems for 30m class telescopes. Based on our original design to achieve
the requirements, prototyping of the device is currently underway using the MEMS development facility in our
university. Second one is a consideration of tomographic algorithm for the wavefront estimation required for
an MOAO system. The algorithm will be tested on a test bench simulating multiple guide stars and wavefront
sensors. Concept design of the test bench is shown. MEMS-DM and MOAO testbed developments will be
concluded by 2013.
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