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

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