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GMT The Giant Magellan Telescope Phasing System Brian McLeod Harvard-Smithsonian Center for Astrophysics.

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Presentation on theme: "GMT The Giant Magellan Telescope Phasing System Brian McLeod Harvard-Smithsonian Center for Astrophysics."— Presentation transcript:

1 GMT The Giant Magellan Telescope Phasing System Brian McLeod Harvard-Smithsonian Center for Astrophysics

2 GMT AO4ELT3 - 30 May 2013 The GMT Phasing Team Systems Engineering Antonin Bouchez - GMTO Integrated Optics Phasing Sensor (IOPS) Francis Bennet - Australian National University Phasing Camera Brian McLeod - Harvard-Smithsonian CfA Pyramid WFS Simone Esposito, Enrico Pinna – INAF Osservatorio Astrofisico di Arcetri M1 Edge sensors D. Scott Acton - Ball Aerospace M2 Edge sensors Roberto Biasi, Mauro Manetti - Microgate 2

3 GMT Telescope Observing Modes Natural Seeing – No phasing necessary Ground Layer AO – No phasing necessary Natural Guidestar AO – Correct telescope segment piston error – Correct atmospheric segment piston error (~120 nm RMS) Laser Tomography AO – Only faint, off-axis natural guidestars available – Therefore, can correct only telescope segment piston error 3AO4ELT3 - 30 May 2013

4 GMT 3-stage approach to phase the telescope to <65 nm RMS in the LTAO observing mode: 1.Initial phasing using off-axis Phasing Camera 2.Maintain alignment over short timescales using M1 & M2 edge sensors 3.Update edge sensor setpoints using the phasing channel of the On- Instrument Wavefront Sensor. Phasing Strategy: LTAO Mode 4AO4ELT3 - 30 May 2013

5 GMT Outline 5 1.The phasing challenge 2.The toolbox 1.Metrology 2.Optical Sensors 3.Compensators 3.Putting it together into a system AO4ELT3 - 30 May 2013

6 GMT GMT Phasing - Challenges Ohara E6 has non-zero CTE (2.8 × 10 -6 /°C) M1 segment separations are large (30-36 cm) 6AO4ELT3 - 30 May 2013

7 GMT Dual segmentation leads to potential for field-dependent segment piston: – Sensitivity: 1 μrad M2 segment tilt compensated by M1 segment tilt leads to 10 nm of segment piston 1’ off-axis. Performance limited by stability of M2 edge sensor system and ability to make piston measurement close to field center Expected uncertainty in current design: 30nm at 10’ 7 Challenges: Field dependent piston AO4ELT3 - 30 May 2013

8 GMT 8 Metrology: M2 Capacitive Edge Sensors (Microgate Corp.) Expected piston sensitivity: 20nm RMS AO4ELT3 - 30 May 2013 Considering alternative layout with additional single-axis sensors (green) to improve tilt sensitivity

9 GMT 9 Metrology: M1 distance interferometers Renishaw distance- measuring interferometers Expected short-term piston sensitivity: 13nm RMS AO4ELT3 - 30 May 2013

10 GMT 10 Optical Sensors: Phasing Camera AO4ELT3 - 30 May 2013 Patrol radius = 6’-10’

11 GMT 11 Optical sensors: Phasing camera: Basics Form pupil image on MEMS array Reimage pupil onto masked lenslet array. EMCCD Shack-Hartmann loop Dichroic Grism array Vis IR Dispersed fringes AO4ELT3 - 30 May 2013

12 GMT 12 Deployed at Magellan July 2012 Optical sensors: Phasing camera: Prototype AO4ELT3 - 30 May 2013

13 GMT 13 Optical Sensors: Phasing camera: Data analysis AO4ELT3 - 30 May 2013

14 GMT For R<15, K<12, median seeing, 60 sec, get RMS<~50 nm with 85% sky coverage at SGP. Fringe capture range is +/- 50 μm 14 Optical Sensors: Phasing camera: performance AO4ELT3 - 30 May 2013 K R nm RMS WFE

15 GMT 15 Optical sensors: Integrated Optic Piston Sensor Poster 13236: Integrated Optic Segment Piston Sensor for the GMT, F. Bennet et al. AO4ELT3 - 30 May 2013

16 GMT 16 IOPS waveguide schematic Optical Sensors: Integrated Optics Piston Sensor AO4ELT3 - 30 May 2013 Opto-mechanical design

17 GMT 17 IOPS Performance Error source NGS 30” off-axis (nm RMS) NGS 60” off-axis (nm RMS) Low order Zernike modes 1639 Residual wavefront526 Residual tip-tilt55 Detector noise22 Wavelength bandwidth 66 Total IOPS Error (nm RMS) 18.647.6 AO4ELT3 - 30 May 2013

18 GMT 3-stage approach to phase the telescope to <65 nm RMS in the LTAO observing mode: 1.Initial phasing using off-axis Phasing Camera 2.Maintain alignment over short timescales using M1 & M2 edge sensors 3.Update edge sensor setpoints using the phasing channel of the On- Instrument Wavefront Sensor. OR Update edge sensor setpoints using Phasing Camera if no star for IOPS LTAO Phasing Strategy Summarized 18AO4ELT3 - 30 May 2013

19 GMT 1.M1 and M2 edge sensor metrology – startup and for high-speed relative measurement 2.Phasing camera 6-10’ off axis – fringe capture and initial setup 3.NGSAO – Dual wavelength pyramid sensor measures telescope+atmosphere 4.LTAO – Integrated Optics Piston Sensor @ 1’ or Phasing Camera @6-10’ (no measurement of atmospheric piston) AO4ELT3 - 30 May 201319 Phasing System Summary


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