Integrated modeling of the GMT laser tomography adaptive optics system

Abstract

Laser Tomography Adaptive Optics (LTAO) is one of adaptive optics systems planned for the Giant Magellan Telescope (GMT). End-to-end simulation tools that are able to cope with the complexity and computational burden of the AO systems to be installed on the extremely large telescopes such as GMT prove to be an integral part of the GMT LTAO system development endeavors. SL95, the Fortran 95 Simulation Library, is one of the software tools successfully used for the LTAO system end-to-end simulations. The goal of SL95 project is to provide a complete set of generic, richly parameterized mathematical models for key elements of the segmented telescope wavefront control systems including both active and adaptive optics as well as the models for atmospheric turbulence, extended light sources like Laser Guide Stars (LGS), light propagation engines and closed-loop controllers. The library is implemented as a hierarchical collection of classes capable of mutual interaction, which allows one to assemble complex wavefront control system configurations with multiple interacting control channels. In this paper we demonstrate the SL95 capabilities by building an integrated end-to-end model of the GMT LTAO system with 7 control channels: LGS tomography with Adaptive Secondary and on-instrument deformable mirrors, tip-tilt and vibration control, LGS stabilization, LGS focus control, truth sensor-based dynamic noncommon path aberration rejection, pupil position control, SLODAR-like embedded turbulence profiler. The rich parameterization of the SL95 classes allows to build detailed error budgets propagating through the system multiple errors and perturbations such as turbulence-, telescope-, telescope misalignment-, segment phasing error-, non-common path-induced aberrations, sensor noises, deformable mirror-to-sensor mis-registration, vibration, temporal errors, etc. We will present a short description of the SL95 architecture, as well as the sample GMT LTAO system simulation results. SL95 RATIONALEEnd-to-end computer simulations have become an integral part of the development of Adaptive Optics (AO) systems. The simulations allow to estimate the AO system performance, guide the designer in the hardware choices, compare different AO modes of operation (Single-Conjugate, Multiple-Conjugate, Multiple-Object, etc.), do system debugging or data reduction tool testing. 1 The importance of AO simulations and the corresponding simulation tools grows even higher at the advent of the Extremely Large Telescopes (ELTs) for which AO becomes an indispensable part. The goal of this work is to present a new end-to-end simulation tool, the Fortran 95 Simulation Library (SL95), which has been created and is being successfully used for development of the Laser Tomography Adaptive Optics (LTAO) system 2 for the Giant Magellan Telescope (GMT). 3 AO for ELTs is extremely computationally demanding, with a requirement of real-time signal processing of ∼ 10 5 sensor measurements at ∼ 1kHz rate to drive ∼ 10 4 Deformable Mirror (DM) actuators. These requi...

The Giant Magellan Telescope adaptive optics program

“…Several AO simulation packages were used to refine the LTAO system design during the preliminary design phase, including the Object Oriented Matlab Adaptive Optics (OOMAO) modeling library 33 , the Yorick Adaptive Optics (YAO) simulation tool 34 , and the Fortran 95 Simulation Library (SL95) 23 . The simulation results presented here were computed with SL95 and capture the following key features of the LTAO system:…”

Simultaneous sodium profile estimation and LGS SH-WFS pixel processing optimization using LGS sub-aperture images

“…Any non-common path aberration (NCPA) further complicates the problem by forcing sub-apertures to operate off null, which magnifies the impact of any non-linearity. Natural guide star (NGS) truth wavefront sensors (TWFS) are therefore often suggested to correct for the sodium profile induced semi-static wavefront aberrations reconstructed from zero-point biases 1 , 3 , 4 …”

“…Natural guide star (NGS) truth wavefront sensors (TWFS) are therefore often suggested to correct for the sodium profile induced semi-static wavefront aberrations reconstructed from zero-point biases. 1,3,4 The Thirty Meter Telescope (TMT) narrow field infrared AO system (NFIRAOS) 5 is a multiconjugate adaptive optics system with two deformable mirrors, six LGS WFS, and a pyramid WFS used for truth wavefront sensing, or as a high order NGS WFS operating in classic NGS AO mode. In addition, NFIRAOS supports up to three on instrument WFS (OIWFS) for tip/tilt/ focus (TTF) and plate scale sensing, as well as up to four on detector guide windows in science instruments to either correct OIWFS NCPA or provide fast tip/tilt and plate scale sensing themselves.…”

Simulation and analysis of co-phasing errors of the segmented primary mirror tiled by hexagonal segments in LOT

“…RMS value of the wavefront of TMT decrease from 40 µm to 400 nm. The RMS value of piston is about 30 nm after the fine co-phasing process (Nelson 2000;Ellerbroek et al 2005;Baffes et al 2008;Sanders 2013;Piatrou & Chanan 2011). Mitchell Troy and Gray Chanan from USA analyzed the influence of gaps, secondary mirror obstruction and reflectivity of mirrors on the performance of TMT (Troy & Chanan 2003).…”