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A Real-Time Controller Architecture for the Multi-Conjugate Adaptive Optics System on the Thirty Meter Telescope

Abstract 157

Submitted by Stephen BROWNE


S. Browne, G. Tyler, J. Vaughn, C. Vogel


The Optical Sciences Company and Montana State University


We present the result of a Trade Study for the processing architecture of the Narrow Field Infrared Adaptive Optics System (NFIRAOS) Real Time Controller (RTC) that will be one of the early-light instruments on the next-generation 30 m telescope being developed by the TMT Observatory Corporation. The RTC and NFIRAOS will provide multi-conjugate atmospheric correction (MCAO) employing 2 deformable mirrors (DMs) and six sodium Laser Guide Stars (LGSs). Six Shack-Hartmann wavefront sensors (WFSs) with 60 x 60 subapertures each will be analyzing the LGS light returned from the Earth’s sodium layer. A newly developed camera with a polar-coordinate pixel array will be used with each LGS WFS to provide linear position estimation of the Hartmann spots, even though the spots will generally be radially elongated due to the thickness of the sodium layer. The RTC will perform atmospheric tomography from the 6 LGS WFS so that the two DMs can apply their wavefront corrections to the appropriate altitude and therefore correct over a relatively wide field of view (FOV). The exact method for solving the tomography problem given the WFS images, has been one of the subjects of this study. We show that our architecture can achieve complete LGS tomography, wavefront reconstruction, DM fitting, and actuator servo control, in 436 microseconds using a single processing board which contains a reasonable complement of today’s in-production field-programmable gate arrays (FPGAs). We further show that our architecture can support a 120 x 120-subaperture upgrade to NFIRAOS with 436-microsecond processing per frame, using only four boards.