Donald Gavel (UCO/Lick Observatory, UC Santa Cruz)
Keywords: Adaptive Optics
Abstract:
We report on experimental results with adaptive optics testbeds at the UCO/Lick Observatory. One testbed is dedicated to high contrast AO imaging and is a prototype for a ground-based extrasolar planet imager. The second testbed is dedicated to developing concepts and architectures for multi-laser guidestar tomography in wide-field AO applications. Concurrent with the testbed experiments we are evaluating the new components and key technologies applicable to the next generation of AO systems including MEMS deformable mirrors, high speed low noise detectors, wavefront sensing methods, and fast wavefront control processors. The high contrast testbed has achieved its contrast goal of better than 10^-6 in a 5 to 15 lambda/d region around the central star, the “discovery region,” using a 1024 actuator MEMS deformable mirror correcting typical atmospheric aberrations. A new section of the testbed has been added recently which will contain an advanced concept apodized pupil Lyot coronagraph for which some initial results will be attained in time for this conference. We now progressing with the design phase of the Gemini Planet Imager instrument for which we are developing a 4096 actuator MEMS device. The Multi-guidestar Tomography testbed has been configured to analyze MCAO and MOAO architectures under consideration for the Keck and proposed Thirty Meter Telescope AO systems. These configurations will consist of from 5 to 9 laser guidestars spread out on a field of between 2 and 5 arcminutes diameter. Testbed results are clearly showing the extension of the high-Strehl correction field out to these wide fields, which are much larger than the isoplanatic angle. As part of this project, we have developed high-speed tomography algorithms for efficient minimum-variance estimation and control of wavefronts. We have also scoped and prototyped the specialized compute hardware necessary to implement them in real-time. In the component development area we are investigating the use of MEMS deformable mirrors for open-loop control of wavefronts. This will enable the multi-object AO (MOAO) configuration that is suited to simultaneous multi-object spectroscopy, an architecture that multiplies the efficiency of science observing on large telescopes. Since the actuation of MEMS deformable mirrors is based on a very repeatable and low hysteresis electrostatic deflection process, they show great promise for this their use in this approach. Present go-to accuracies have been demonstrated to on the order of 15nm rms. MEMS are also small and lower in cost than current generation piezo actuator DMs, which implies that they have potential for additional applications throughout the AO optical system. We are investigating applications in the high-order wavefront and tip/tilt sensors.
Date of Conference: September 12-15, 2007
Track: Adaptive Optics