The TMT Adaptive Optics Program

Transcription

1 The TMT Adaptive Optics Program Brent Ellerbroek a, Sean Adkins b, David Andersen c, Jenny Atwood c, Arnaud Bastard d, Yong Bo e, Marc- André Boucher c, Corinne Boyer a, Peter Byrnes c, Kris Caputa c, Shanqiu Chen f, Carlos Correia c, Raphael Cousty d, Joeleff Fitzsimmons c,luc Gilles a, James Gregory g, Glen Herriot c, Paul Hickson h, Alexis Hill c, John Pazder c, Hubert Pages d, Thomas Pfrommer h, Vladimir Reshetov c, Scott Roberts c, Jean-Christophe Sinquin g, Matthias Schoeck c, Malcolm Smith c, Jean-Pierre Veran c, Lianqi Wang a, Kai Wei f, and Ivan Wevers c a TMT Observatory Corporation, b W. M. Keck Observatory, c Herzberg Institute of Astrophysics, d CILAS, e Technical Institute of Physics and Chemistry, f Institute of Optics and Electronics, g MIT Lincoln Laboratory, h University of British Columbia Adaptive Optics for Extremely Large Telescopes Victoria, Canada September 26,

2 Presentation Outline! First light requirements for adaptive optics (AO) at TMT! Derived architecture and technology choices! System overview; major changes since 2009! Subsystem design tradeoffs and progress Narrow Field IR AO System (NFIRAOS) Laser Guide Star Facility (LGSF)! AO component development! Modeling and system performance analysis! Further First Decade AO systems and upgrades! Summary 2

3 AO Requirements at TMT Early Light! High throughput (85% in J, H, K, and I bands)! Low thermal emission (15% of sky + telescope)! Diffraction-limited near IR image quality [187, 191, 208] nm wavefront error over a [0,10,30] arc sec field! High sky coverage (50% at galactic pole)! High photometric accuracy 2% over 30 arc sec at λ=1 µm for a 10 minute observation! High astrometric accuracy 50 µas over 30 arc sec in H band for a 100 second observation! High observing efficiency! Available at first light with low risk at acceptable cost 3

4 Derived Architectural Decisions! Cooled (-30C) optical system for required emission! High order (60x60) wavefront compensation for required wavefront quality! Multi-conjugate AO (MCAO) with 6 guide stars and 2 deformable mirrors for required fields-of-view and astrometric/photometric accuracy! Laser guide star (LGS) AO for sky coverage! Tip/tilt and tip/tilt/focus NGS wavefront sensing in the near IR with a 2 arc min patrol field for sky coverage 4

5 TMT First Light AO: Laser Guide Star Facility (LGSF)! Sum-frequency Nd:YAG or frequency-doubled Raman fiber laser systems! Lasers mounted on telescope elevation journal! Conventional beam transfer optics (mirrors)! Center-launch beam projection 5

6 TMT First Light AO: Narrow Field IR AO System (NFIRAOS)! Mounted on Nasmyth Platform! Interfaces for 3 client instruments! Piezostack deformable mirrors and tip/tilt stage! Polar coordinate CCD array for the LGS WFS! HgCdTe CMOS arrays for low order, NGS, infrared WFSs (in client instruments) 6

7 TMT First Light AO: Real Time Control (RTC) System Features! Hard real time processes: WFS pixel processing (matched filtering) Atmospheric tomography! Split NGS/LGS formulation! Minimal variance, pseudo open-loop! Computationally efficient DM fitting Temporal filtering! Background tasks Matched filter updating Cn2 estimation (SLODAR) Offload to M1, M2 WFS telemetry for PSF reconstruction 7

8 Project Participants UBC, Vancouver (Sodium LIDAR) TOPTICA, Munich (Laser Systems) TIPC, Beijing (Laser Systems) HIA, Victoria (NFIRAOS) DRAO, Penticton (RTC) MIT/LL, Lexington (WFS CCDs) CILAS, Orleans (Wavefront Correctors) IOE, Chengdu (Laser Guide Star Facility) Keck Observatory, Waimea (WFS readout electronics) tosc, Anaheim (RTC) TMT, Pasadena (Management, SE) 8

9 What s Happened Since 2009?! New NFIRAOS opto-mechanical design eliminates field distortion! LGSF architecture review Center- vs. side-launch trade study New laser location for new smaller, lighter, gravity invariant designs! AO component design and prototyping Laser systems Deformable mirrors (and DM electronics) CCDs (and electronics) for LGS and visible NGS wavefront sensors IR HgCdTe detectors for low order, IR NGS wavefront sensors! AO system models and performance estimates! Concept development and performance estimates for First Decade AO system options 9

10 Field Distortion and NFIRAOS! 2009 NFIRAOS optical design was a off-axis parabola (OAP) relay Good image quality 0.4 arc sec distortion at edge of field! Distortion rotated with field at final science instrument focal plane Unacceptable for astrometry and multiobject spectroscopy! Several re-design options were considered: Output foci OAP DM at h=0 km on tip/ tilt platform OAP DM at h=11.2 km From telescope Image derotator at NFIRAOS input 4-mirror anastigmat optical design Dual optical relay with 4 OAPs additional surfaces; congested input focus large aspherics; difficult packaging additional surfaces; larger mass & volume Symmetric, refractive optical design chromatic aberrations; not seriously studied 10

11 Original (Left) and Updated (Right) NFIRAOS Optics (Common Scale) Output focus OAP OAP DM0 and TTS DM0 and TTS OAP DM 11.2 OAP OAP DM 11.2 OAP Input focus 11

12 NFIRAOS Simplified Block Diagram (LGS Mode) WFS/DM telemetry (PSF recon) 6 LGS NGS(s) Sci. Obj. RTC Param. Gen. Source sims. Reconstruction params. OAP DM/WFS Statistics Telescope offloads RTC DM11 OAP OAP DM0 + TTS Phase screen To zoom Actuator commands field selection mirrors OAP LGS BS SCI BS OAP OAP NGS WFS Truth WFS Flip mirror for NGS mode LGS Zoom Inst. Fold LGS Off- Sets LGS Grads 6 LGS WFS On Inst. WFS(s) NGS Grads To Sci. Instrument 12 Simplifications

13 LGSF Circa 2009! Laser System within telescope azimuth structure For large lasers requiring a fixed gravity vector, frequent alignment and maintenance! LLT behind M2 Minimizes LGS elongation; was also thought to minimize wavefront error due to noise! Mirror-based beam transport between the lasers and the LLT Lasers 13

14 LGSF Redesign Options Considered! Center launch, with lasers mounted in elevation structure No need to transfer beams from azimuth to elevation structure Reduced overall path length Feasible with new lighter, smaller, gravity-invariant laser systems! vs. Side-launch, with lasers mounted in M1 cell Modest (~20 nm RMS) performance advantage for equal LGS signal Simplified beam transport, at expense of multiple LLTs Tighter laser packaging; larger, rotating LGS elongation on WFSs! Various LLT simplifications also implemented, independent of above trades 0.4m diameter; no imaging of stars for alignment; new reflective and refractive design options! LGS acquisition sensor added 14

15 Laser launch location Updated LGSF Layout Diagnostics Bench Asterism Generator Beam transfer optics path Laser location Acquisition Sensor Launch Telescope 15

16 Largest variations ~20nm RMS for expected WFS noise levels AO Performance Estimates: Side versus Center Launch

17 ! Four atmospheric effects studied Rayleigh backscatter causes fratricide Remaining effects will degrade LGS signal level Effects Backscatter Optical Depth Rayleigh Strong 0.04 Ozone Weak 0.03 Aerosol Weak 0.02 Cirrus Weak <0.22 LGS Fratricide Modeling! Combined error budget allocation Cn2 Profile 25% MK13N 50% MK13N Zenith angle (deg) RMS WFE, nm

18 AO Component Requirement Summary Deformable mirrors 63x63 and 76x76 actuators at 5 mm spacing Tip/tilt stage 10 µm stroke and 5% hysteresis at -30C 500 µrad stroke with 0.05 µrad noise 20 Hz bandwidth NGS WFS detector 240x240 pixels LGS WFS detectors Low-order IR NGS WFS detectors ~0.8 quantum efficiency,~1 electron at Hz 60x60 subapertures with 6x6 to 6x15 pixels each ~0.9 quantum efficiency, 3 electrons at 800 Hz 1024x1024 pixels (subarray readout on ~8x8 windows) ~0.6 quantum efficiency, 3 electrons at Hz Real time controller Solve 35k x 7k reconstruction problem at 800 Hz Sodium guidestar lasers 25W (20W with backpumping), M 2 < 1.17 Coupling efficiency of 130 photons-m 2 /s/w/atom 18

19 ! Deformable mirrors (CILAS) Component Development Highlights Since 2009 Final design of NFIRAOS DMs 6x60 subscale prototype in progress! Visible WFS detectors (Keck and MIT/LL) Prototype wafer run of LGS and NGS WFS CCDs completed Frontside testing of packaged devices in progress! IR NGS WFS detector arrays (Teledyne and Caltech) Read noise tests of H2RG detector <3 noise electrons at required rates with correlated multiple sampling! Guidestar laser systems TOPTICA Raman Fiber laser design and prototyping with ESO, Keck TIPC Nd:YAG SFG laser design, prototyping, and on-sky tests! Development of WFS readout electronics (Keck) and DM drive electronics (HIA) also progressing 19

20 NFIRAOS Deformable Mirrors! Prototyping and design contract now underway at CILAS: Develop Final DM Designs for NFIRAOS Fabricate and test 6x60 DM breadboard Qualify new piezo material source Validate FEA models for thermal effects (Re)Validate actuator electrical contacting Confirm long-term facesheet stability Integrated testing with DM drive electronics at HIA to follow DM0 Assembly Drawing DM11.2 Baseplate Mode DM 6x60 breadboard FEA model of thermal effects in DM0 20

21 Polar Coordinate CCD Array Concept for Wavefront Sensing with Elongated LGS sodium layer ΔH =10km Fewer illuminated pixels reduces pixel read rates and readout noise H=100km D = 30m è Elongation 3-4 LLT TMT AODP Design

22 NFIRAOS Visible Wavefront Sensor Detector Prototyping! Prototype wafer fab run completed(!) 30x30 subaperture quadrant of polar coordinate LGS WFS CCD visible NGS WFS CCD! Good functional results in wafer-level probing! Polar coordinate devices now diced, packaged, and ready for testing Frontside Device CCID-74 (256 2 ) CCID-61 Polar Coordinate Detector Prototype Frontside Package Image of the front side of a finished wafer

23 Laser System Development! TOPTICA/MPB Keck/TMT involvement in ESO contract for VLT 4LGSF laser system! TIPC design/prototyping study 20W field test prototype laser tested on the sky (8.7 mag. LGS) Further testing planned in 2012 at Univ. British Columbia LZT Lidar Toptica/MPB Raman Fiber Laser On-sky TIPC tests in Yunnan TIPC Nd:YAG SFG Laser 23

24 Principal AO Simulation Tools! End-to-end time domain simulation code Measured sodium layer profiles Von Karman, multilayer turbulence with frozen flow Telescope optics figure/alignment errors + tip/tilt jitter Physical optics modeling for LGS beacons, LGS/NGS WFS spots, and science PSFs Faithful implementation of hard RTC processes GPU implementation; ratio between wall clock and NFIRAOS time! Simulation postprocessor for sky coverage analysis One history of higher-order wavefront correction replayed for multiple NGS asterisms, since higher-order correction decoupled from NGS loop Sky coverage statistics generated using 500+ random NGS asterisms! Supplementary models/codes for individual studies 24

25 Sample Simulation Studies Since 2009! AO Error budget maintenance: RMS wavefront error and sky coverage! Subsystem and component trade studies LGS WFS issues: Center- vs. side-launch; fratricide; LGS spot size; meteors DM issues: stroke, flatness, and failed actuator impact TMT optics: Mirror OPDs, M1 actuators/sensors; input pupil misalignment NFIRAOS optics: Off-axis aberrations; NCPA; LGS WFS pupil distortion Vibration issues: M2/M3 tracking, tip/tilt stage power dissipation! RTC algorithms Hard real-time: WFS pixel processing; tomography; DM fitting; Kalman filtering Background tasks: SLODAR; PSF reconstruction! PSF modeling for science simulations Galactic center PSF uniformity and image distortion; slit throughput 25

26 Top-Level AO Performance Estimate Error term On-axis RMS WFE, nm Overall on-axis wavefront error 187 LGS mode error 157 First-order turbulence compensation 126 Implementation errors 93 Opto-mechanical 75 AO component and higher-order effects 56 NGS mode error 52 Contingency 88 Median Seeing, 50% sky coverage at the Galactic Pole Estimate stable since

27 Estimated Sky Coverage with Median Seeing Galactic Longitude (deg) Prob(WFE < 191 nm) for Hour Angle = 0! Prob. > 75% at north galactic pole! Prob. ~ 100% below 30 degrees galactic latitude Galactic Longitude (deg) 27

28 Options for Additional First Decade AO Systems and Upgrades! Adaptive secondary mirror Enables ground layer AO (GLAO) for wide field spectroscopy Simplifies other AO system architectures Correction of modes under consideration! Mid Infra-Red AO (MIRAO) facility 3 LGS, order 30x30 correction for observations from 4.5 to 25 µm! Planet Formation Instrument (PFI) high contrast imaging system contrast in H for first-generation system; for second Advanced MEMs, coronagraphs/nullers, first- and second-stage WFSs! Multi-Object AO (MOAO) for IR multi-object spectroscopy (IRMOS) ~20 IFUs with 50 mas pixels deployable on a 5 arc minute field! NFIRAOS upgrades for smaller wavefront error and/or improved correction on the full 2 arc min NFIRAOS technical field 28

29 Concepts from 2006 Instrument Feasibility Studies MIRAO (NOAO/ Univ. Hawaii IFA) PFI (Lawrence Livermore/ U. Montreal/ UC Berkeley/ JPL/ Comdev IRMOS (Caltech) IRMOS (U. Florida/ HIA) 29

30 NFIRAOS Upgrade Concepts! Classical dual conjugate AO! Hybrid MOAO! Tri conjugate MCAO! Order DMs! Reduces on-axis WFE! Could use adaptive M2 woofer! Order MEMS! Reduces WFE over full 2 arc min! Order MEMS! Reduces WFE over 30 arc sec 30

31 Performance Estimates for NFIRAOS Upgrades Upgrade Option LGS photon return On axis WFE, RMS nm WFE at 15, RMS nm Baseline NFIRAOS Upgrade NFIRAOS DMs New MOAO or MCAO NFIRAOS Instrument First light estimate First light estimate First light estimate 2x first light estimate (or pulsed laser)

32 Summary! Since 2009, the TMT first light AO architecture has benefited from two significant refinements: NFIRAOS 4-OAP, distortion-free optical design form LGSF center launch option with lasers on elevation structure! Component development progress is continuing Deformable mirrors Wavefront sensing detectors Guidestar lasers!! Enhanced modeling capabilities predict performance requirements will be met From the final report of the Astro2010 Panel on Optical and Infrared Astronomy from the Ground: TMT has completed a preliminary design for their first light AO system NFIRAOS, which could be constructed today using existing technologies. 32

33 Acknowledgements! The TMT Project gratefully acknowledges the support of the TMT partner institutions.! They are the Association of Canadian Universities for Research in Astronomy (ACURA), the California Institute of Technology China's TMT consortium (CTMT) and the University of California.! This work was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the Ontario Ministry of Research and Innovation, the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the British Columbia Knowledge Development Fund, the Association of Universities for Research in Astronomy (AURA) the U.S. National Science Foundation the Key International Cooperation Programs of the National Natural Science Foundation of China (NSFC) and the Chinese Academy of Sciences 33