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Wang L.,Thirty Meter Telescope Project | Gilles L.,Thirty Meter Telescope Project | Ellerbroek B.,Thirty Meter Telescope Project | Correia C.,University of Porto
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

We have implemented the linear quadratic Gaussian (LQG) controller in our physical optics sky coverage simulator (MAOS) for the Thirty Meter Telescope (TMT) Narrow Field InFrared Adaptive Optics System (NFIRAOS) aimed for improved correction of tip/tilt and plate scale modes. The LQG controller has a built-in capability to correct narrow frequency vibrations that are above the closed loop bandwidth of the system and is a very desirable solution for this application. The LQG controller is tuned with the combined power spectral density (PSD) of turbulence, wind shake, and vibration computed from the telemetry. We will show how LQG performs for various telescope/instrument vibration spectral (such as broadband or drifting peaks). We will also show the performance and sky coverage of LQG in comparison with single or double integrator controllers for correcting low order atmospheric turbulence with a set of up to three tip/tilt(/focus) natural guide star wavefront sensors. We found that the LQG controller reduces the median sky coverage wavefront error by 25 nm in quadrature. © 2014 SPIE.


Wang L.,Thirty Meter Telescope Project | Ellerbroek B.,Thirty Meter Telescope Project
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The adaptive optics (AO) simulations at the Thirty Meter Telescope (TMT) have been carried out using the efficient, C based multi-threaded adaptive optics simulator (MAOS, http://github.com/lianqiw/maos). By porting time-critical parts of MAOS to graphical processing units (GPU) using NVIDIA CUDA technology, we achieved a 10 fold speed up for each GTX 580 GPU used compared to a modern quad core CPU. Each time step of full scale end to end simulation for the TMT narrow field infrared AO system (NFIRAOS) takes only 0.11 second in a desktop with two GTX 580s. We also demonstrate that the TMT minimum variance reconstructor can be assembled in matrix vector multiply (MVM) format in 8 seconds with 8 GTX 580 GPUs, meeting the TMT requirement for updating the reconstructor. We also benchmarked applying MVM in GPUs and got 1.7 ms end-to-end latency with 7 GTX 580 GPUs. © 2012 SPIE.


Wang L.,Thirty Meter Telescope Project | Gilles L.,Thirty Meter Telescope Project | Ellerbroek B.,Thirty Meter Telescope Project
Applied Optics | Year: 2011

The scientific utility of laser-guide-star-based multiconjugate adaptive optics systems depends upon high sky coverage. Previously we reported a high-fidelity sky coverage analysis of an ad hoc split tomography control algorithm and a postprocessing simulation technique. In this paper, we present the performance of a newer minimum variance split tomography algorithm, and we show that it brings a median improvement at zenith of 21nm rms optical path difference error over the ad hoc split tomography control algorithm for our system, the Narrow Field Infrared Adaptive Optics System for the Thirty Meter Telescope. In order to make the comparison, we also validated our previously developed sky coverage postprocessing software using an integrated simulation of both high- (laser guide star) and low-order (natural guide star) loops. A new term in the noise model is also identified that improves the performance of both algorithms by more properly regularizing the reconstructor. © 2011 Optical Society of America.


Zhang X.-F.,Beijing Institute of Technology | Wang L.-Q.,Thirty Meter Telescope Project
Research in Astronomy and Astrophysics | Year: 2014

Adaptive optics (AO), which provides diffraction limited imaging over a field-of-view (FOV), is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor (WFS) is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors (DMs). This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope (pointing toward zenith) is related to atmospheric anisoplanatism. We theoretically quantify the performance of the tomographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10″-80″ diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric properties at ground level, and present the optimum DM conjugate altitudes for different observation sites. © 2014 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.


Wang L.,Thirty Meter Telescope Project | Andersen D.,Herzberg Institute for Astrophysics | Ellerbroek B.,Thirty Meter Telescope Project
Applied Optics | Year: 2012

The scientific productivity of laser guide star adaptive optics systems strongly depends on the sky coverage, which describes the probability of finding natural guide stars for the tip/tilt wavefront sensor(s) to achieve a certain performance. Knowledge of the sky coverage is also important for astronomers planning their observations. In this paper, we present an efficient method to compute the sky coverage for the laser guide star multiconjugate adaptive optics system, the Narrow Field Infrared Adaptive Optics System (NFIRAOS), being designed for the Thirty Meter Telescope project.We show that NFIRAOS can achieve more than 70% sky coverage over most of the accessible sky with the requirement of 191 nm total rms wavefront. © 2012 Optical Society of America.


Wang L.,Thirty Meter Telescope Project
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes | Year: 2013

In this paper, we present a CPU+GPU based RTC design for the Thirty Meter Telescope (TMT) Narrow Field Infrared AO System (NFIRAOS), as part of an on-going trade study of control algorithms and processor hardware options. We demonstrate that the system will meet the stringent latency requirement of first computing gradients for ~15500 laser guide star wavefront sensor sub-apertures, and then commands for ~7000 deformable mirror actuator at 800 Hz, using 12 Nvidia GTX 580 GPUs (2 GPUs per WFS) or 6 Nvidia GTX 590 boards. A classical matrix vector multiply reconstruction algorithm is used for its simplicity and parallelizability. The control matrix implements a minimum variance wavefront reconstruction algorithm and is computed columnby- column using an iterative solver. We demonstrate that we can initialize the control matrix in about 1 minute and update it in 10 seconds as operating conditions vary to maintain optimal performance. Finally, we will show a first version of the complete block diagram of data flow and mapping to hardware.


Simard L.,Thirty Meter Telescope Project | Simard L.,National Research Council Canada | Crampton D.,National Research Council Canada | Ellerbroek B.,Thirty Meter Telescope Project | Boyer C.,Thirty Meter Telescope Project
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

An overview of the current status of the Thirty Meter Telescope (TMT) instrumentation program is presented. Science cases and operational concepts as well as their links to the instruments are continually revisited and updated through a series of workshops and conferences. Work on the three first-light instruments (WFOS IRIS, and IRMS) has made significant progress, and many groups in TMT partner communities are developing future instrument concepts. Other instrument-related subsystems are also receiving considerable attention given their importance to the scientific end-toend performance of the Observatory. As an example, we describe aspects of the facility instrument cooling system that are crucially important to successful diffraction-limited observations on an extremely large telescope. © 2012 SPIE.


Rogers J.,Thirty Meter Telescope Project | Thompson H.,Thirty Meter Telescope Project
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The Thirty Meter Telescope is comprised of thirty five individual sub-systems which include optical systems, instruments, adaptive optics systems, controls, mechanical systems, supporting software and hardware and the infrastructure required to support their operation. These thirty five sub-systems must operate together as a system to enable the telescope to meet the science cases for which it is being developed. These science cases are formalized and expressed as science requirements by the project's Science Advisory Committee. From these, a top down requirements engineering approach is used within the project to derive consistent operational, architectural and ultimately detailed design requirements for the sub-systems. The various layers of requirements are stored within a DOORS requirements database that also records the links between requirements, requirement rationale and requirement history. This paper describes the development of the design requirements from science cases, the reasons for recording the links between requirements and the benefits that documenting this traceability will yield during the design and verification of the telescope. Examples are given of particular science cases, the resulting operational and engineering requirements on the telescope system and how individual sub-systems will contribute to these being met. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Wang L.,Thirty Meter Telescope Project | Otarola A.,Thirty Meter Telescope Project | Ellerbroek B.,Thirty Meter Telescope Project
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Laser beams projected from the ground to form laser guide stars (LGS) experience scattering and absorption that reduce their intensity as they propagate through the atmosphere. Some fraction of the scattered light will be collected by the other LGS wavefront sensors and causes additional background in parts of the pupil. This cross-talk is referred to as the fratricide effect. In this paper we quantify the magnitude of four different sources of scattering/absorption and back scattering, and evaluate their impact on performance with various zenith angles and turbulence profiles for the Thirty Meter Telescope (TMT) MCAO system, NFIRAOS. The resulting wavefront error is on the order of 5 to 20 nm RMS, provided that the mean background from the fratricide can be calibrated and subtracted with an accuracy of 80%. We have also found that the impact of fratricide is a weak function of LGS asterism radius. © 2010 SPIE.


Wang L.,Thirty Meter Telescope Project | Otarola A.,Thirty Meter Telescope Project | Ellerbroek B.,Thirty Meter Telescope Project
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2010

Laser beams projected from the ground to form sodium layer laser guide stars (LGSs) for adaptive optics (AO) systems experience scattering and absorption that reduce their intensity as they propagate upward through the atmosphere. Some fraction of the scattered light will be collected by the other wavefront sensors and causes additional background in parts of the pupil. This cross-talk between different LGS wavefront sensors is referred to as the fratricide effect. In this paper we quantify the magnitude of four different sources of scattering/ absorption and backscattering, and we evaluate their impact on performance with various zenith angles and turbulence profiles for one particular AO system. The resulting wavefront error for the Thirty Meter Telescope (TMT) multi-conjugate AO (MCAO) system, NFIRAOS, is on the order of 5 to 20 nm RMS, provided that the mean background from the fratricide effect can be calibrated and subtracted with an accuracy of 80%. We also present the impact on system performance of momentary variations in LGS signal levels due to variations in cirrus absorption or laser power, and we show that this affects the performance more than does an equal variation in the level of the fratricide. © 2010 Optical Society of America.

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