Abstract
Closed-loop adaptive optics systems that use minimum mean square error wavefront reconstruction require the computation of pseudo open-loop wavefront slopes. These techniques incorporate a knowledge of atmospheric statistics that must therefore be represented within the wavefront slope measurements. These pseudo open-loop slopes are computed from the sum of the measured residual slopes and the reconstructed slopes that would be given if the deformable mirror was flat, generally involving the multiplication of an interaction matrix with actuator demands from the previous time-step. When using dense algebra, this multiplication is computationally expensive for Extremely Large Telescopes, requiring a large memory bandwidth. Here, we show that this requirement can be significantly reduced, maintaining mathematical correctness and significantly reducing system complexity. This therefore reduces the cost of these systems and increases robustness and reliability.N
Highlights
Adaptive optics (AO; Babcock 1953; Hardy 1998) is a mainstream technology, and essential for the generation of Extremely Large Telescopes (ELTs), including the European Southern Observatory ELT, the Thirty Metre Telescope (TMT), and the Giant Magellan Telescope, which will have light collecting areas equivalent to primary mirror diameters of at least 20 m
We concentrate on ELT systems, including single conjugate AO (SCAO), laser tomographic AO (LTAO), multiconjugate AO (MCAO), and multiobject AO (MOAO), mapping these designs to currently available computational hardware
We find that the maximum wavefront sensors (WFSs) frame rate that can be processed using the explicit pseudo open-loop (POL) calculation is 500 Hz, while when using implicit POL calculation, this increases to 600 Hz, due to the reduced memory bandwidth requirement
Summary
Adaptive optics (AO; Babcock 1953; Hardy 1998) is a mainstream technology, and essential for the generation of Extremely Large Telescopes (ELTs) , including the European Southern Observatory ELT, the Thirty Metre Telescope (TMT), and the Giant Magellan Telescope, which will have light collecting areas equivalent to primary mirror diameters of at least 20 m. To optimize AO performance, for wide field of view systems and at low signal levels, it is necessary to use minimum variance wavefront reconstruction techniques (Ellerbroek, Gilles & Vogel 2003), known as minimum mean square error or maximum a posteriori reconstruction. These methods use atmospheric statistics to optimize the wavefront reconstruction. To do this, they must rely on having open-loop slope measurements as input, i.e. those that represent the statistics of the atmosphere, rather than the residual slope measurements more commonly used by single conjugate AO (SCAO) systems. Given that all proposed AO systems for the ELTs operate in closed-loop (or partial closed-loop in the case of MOSAIC Hammer et al 2014), the latter technique must be used
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