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Woofer-Tweeter motivation
Problem:
- High order / high stroke DMs are required for AO correction on TMT but not readily available
Solution: Split the correction between 2 DMs
- A large stroke small order one: the woofer
- A small stroke high order one: the tweeter
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Purpose of the UVic Woofer-Tweeter experiment
- Woofer-tweeter architecture has never been deployed in an AO system.
- Design, simulate and evaluate experimentally algorithms for woofer-tweeter
control.
TMT instruments requiring a WT architecture
NFIRAOS
- The “baseline” version of NFIRAOS (10x10 arcsec corrected
field) will require T/T correction to be split between DM (tweeter)
and T/T plateform (tweeter).
- The “upgrade” version of NFIRAOS (30x30 arcsec corrected
field) will require a 2.5 mm actuator spacing ground DM, which can only
be manufactured with a limited stroke (~ 2 microns).
Woofer will be the adaptive secondary mirror.
MOAO/IRMOS
- DM in each arm will like be a MEMs DM with limited stroke
- Woofer will be required either
- Low order DM in each arm or
- Adaptive secondary acting as a global (ground layer) woofer.
PFI
- Very high order but low stroke (MEMs) tweeter
- Low order woofer (can be adaptive secondary)
- Woofer / tweeter architecture already planned for Gemini ExAOC.
Woofer Tweeter Hardware
Tweeter (Boston Micromachines MEMS)
- 140 actuators positioned in a square 12x12 grid,
- Actuator pitch: 300micron
- PV stroke: 1.2micron
- Pupil diameter: 3mm
Woofer (LAOG (France) magnetic mirror)
- 52 actuators positioned on a 8x8 square grid,
- Actuator pitch: 2.5 mm,
- PV stroke: 25micron,
- Pupil diameter: 16mm,
Tip-tilt stage
- mirror diameter: 35 mm
- scanning frequency: 1kHz
WFS
- 10x10 lenslet array
- Pitch: 188micron
- Focal length: 8 mm
- DALSA camera (up to 750 Hz frame rate)
RTC
- PC Linux
- 400 Hz (one frame delay)
Hot air turbulence generator
- D/r0 between 10 and 50 (exceeds tweeter dynamic range)
- Characterized with WFS
- Phase screen turbulence generator under development
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