The performance of high-contrast AO instruments (GPI, SPHERE, ScEXAO, MagAO) and other systems that operate at visible wavelengths can be severely hampered by control system latencies and temporal wavefront errors. In high-contrast systems, temporal errors and delays are manifest as high spatial frequency wavefront residuals that scatter light into the controllable region of the PSF and diminish contrast, an effect that is particularly severe when atmospheric coherence times are short. Solutions that have been proposed include lower latency electronics, deformable mirrors with lower mechanical response times, and specialized control algorithms such as predictive control. These advancements will be necessary for achieving the latency goals of high actuator count systems on future Extremely Large Telescopes (ELTs), including NFIRAOS+ and PFI on the Thirty Meter Telescope, upgrading the performance of existing highcontrast systems, and pushing adaptive optics to visible wavelengths. LLAMAS (Low-Latency Adaptive Optical Mirror System) is a fully funded adaptive optics system at the Lawrence Livermore National Laboratory site that will test these techniques in an integrated, real time, closed-loop AO system. With a total system latency goal of ~100 microseconds (including mechanical response time, not including frame integration), LLAMAS will achieve an order of magnitude improvement in AO system latencies over the current generation of high-contrast AO systems. The woofer/tweeter architecture will incorporate a 492-actuator Boston Micromachines MEMS device mapping 24 actuators across a circular pupil. The tweeter mirror will be paired with a specialized low-latency driver, delivering less than 40 microseconds electronic and mechanical latency (10 – 90%). The real-time control computer will utilize the computationally efficient Fourier Transform Reconstructor with a predictive Kalman filter with a goal of completing all computations and reconstructing the wavefront in less than 20 microseconds. LLAMAS will be fully integrated with a 21×21 lenslet Shack-Hartmann sensor by January 2019. These proceedings describe the LLAMAS design, characterize the performance of its low-latency componentry, and discuss the relevance of the design for future high-contrast, visiblelight, and high actuator count AO systems on ELTs.
S. Mark Ammons, Brian Bauman, Greg Burton, Chris Gates, Jay Dawson, Brian Hackel, Doug Homoelle, Michael Kim, Glenn Larkin, David W Palmer, Robert Panas, Paul Pax, and Lisa A. Poyneer, "LLAMAS: low-latency adaptive optics at LLNL," Proc. SPIE 10703, Adaptive Optics Systems VI, 107031N (Presented at SPIE Astronomical Telescopes + Instrumentation: June 14, 2018; Published: 18 July 2018); https://doi.org/10.1117/12.2314281.
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