1. High Order Adaptive Optics
A global overview
and the Durham perspective
Nazim Ali Bharmal 2017/Apr/2017

2. Presentation overview
Aim: To justify, explain and introduce examples of HOAO—technical rather than astronomical basis.
Approach:
What is High-Order Adaptive Optics?
Current systems; existing implementations,
Future systems; new implementations,
Durham HOAO; the CHOUGH instrument.

3. 1. Defining HOAO Definition:- There is no standard definition!
Common aspect is highest precision of spatial and temporal sampling and correction.
To compensate for the Earth’s atmosphere, typically
Δr ≃ 15 cm, and Δt ≃ 1 ms
with the result that residual phase is ≤ 100 nm RMS.

4. 1. Defining HOAO HOAO Spatial Resolution SCAO Active optics
0.1m
HOAO
SCAO
0.2m
Spatial Resolution
0.5m
Active optics
Image stabilization 1m
0.1 1 10
100
1000
Speed / Hz

5. Night-time observations & a good observatory site,
1. Defining HOAO
Night-time observations & a good observatory site,
Usually can only operate in best environmental conditions.
Technical challenges are significant,
HOAO systems have common theme of advanced technical implementation.

6. 1. Defining HOAO Requirement: knowledge of the Point Spread Function,
Strehl ratio is then 0.5 to 0.9, visible to near IR.
V-band to J-band
Permits accurate PSF models.
Post-processing
Suppression of on-axis PSF, coronography.
Most advanced HOAO → XAO
(1) Add image of high strehl PSF
(2) High strehl PSF – theoretical PSF
(3) High strehl PSF through coronograph

7. 1. Defining HOAO 
 or  
S=0.28
S=0.42
S=0.63

8. 1. Science drivers
Why do we want such a small wavefront error? Science drivers.
[LIST],
Accurate deconvolution,
Precision solar system science,
Circum-stellar environments including proto-planetary disks and direct exoplanet imaging
Not astrometry, photometry, spectroscopy,

9. 1. Limitations of HOAO Important design limitations,
Higher spatial resolution → smaller sub-apertures for measurements → lower SNR,
Higher temporal resolution → lower exposure times for measurements → lower SNR,
Lower WFE → currently requires smallest field of view,
Limitations in altitude → isochromatic error → practically limits zenith angle.
Graphs of how SNR reduces with more sub-apertures
Same but with shorter exposures and bigger relative lag

10. 1. Typical HOAO design On-axis WFS reference Telescope, primary
Low-speed control loop
High-speed control loop
Telescope
Control system
Low-order DM
High-order DM
(1) Fix arrows, LODM <-> ctrl loop needs double headed arrow
ADC
Primary WFS
Secondary WFS
Instrument

11. 1. Technology advances High-speed wavefront control,
Low power, compact, high-reliability mirror actuators → practical deformable mirrors
High SNR wavefront measurement,
Pyramid and other novel methods → higher SNR
Forward prediction and vibration control,
Kalman-based (LQG) and Fourier algorithms → improved transfer rejection function
Improved measurement,
Pupil position measurement and dynamic interaction matrices → precision measurement and control

12. 1. Examples of sub-systems
Low/Medium-Order DM
~ actuators
~Ø0.75m
Courtesy Microgate Srl
Italy

13. 1. Examples of sub-systems
Low-Order DM
247 actuator DM
Ø39mm
Courtesy ALPAO SaS
France
Medium-/High-Order DM
~ actuator MEMS DM
9.2mm × 9.2mm active area
Courtesy Boston Micromachines Corp.
USA

14. 1. Examples of sub-systems
High-Order DM
3200 actuator DM
~Ø150mm
Courtesy SPIE
Newsroom

15. 1. Examples of sub-systems
Atmospheric Dispersion Compensator
Custom optical design, highly dependent on use case
University of Durham
& UK Astronomy Technology Centre

16. 1. Examples of sub-systems
Imaging & Microscopy
High-resolution WFS
(typical) >500 sub-apertures
← Pyramid
↓ Quadrant-cell SH
University of Durham

17. 1. Examples of sub-systems
Focal plane WFS For NCPA measurement
A&A, 593, A33 (2016)
Calibration & Alignment WFS
For AO assessment and calibration
University of Durham
Differential tip/tilt sensor coronography alignment
Courtesy ESO/SPIE

18. 1. Summary Concept of HOAO, Goals for AO correction,
Control loop architecture,
Advanced technologies,
HOAO ⇔ XAO.

19. 2. Review of existing HOAO
Discuss four HOAO implementations,
Palm 3000 (Palomar 5m telescope, California),
SCExAO (Subaru 8.2m telescope, Hawaii),
MagAO (Magellan Clay 6.5m telescope, Chile),
and FLAO (Large Binocular Telescope, Arizona)
SAXO (VLT 8m telescope, Chile).

20. 2. PALM-3000
doi: / X/776/2/130
Courtesy Astrophysical Journal,
Note Palm-241 as predecessor
No LGS capability

21. 2. SCExAO
Courtesy IoP doi: /682989

22. 2. MagAO
ASM
Courtesy ????

23. 2. MagAO
Courtesy ????

24. 2. SAXO, SPHERE
Courtesy ????

25. 2. Summary SCAO → the WFS and the DM are coupled, Integrated ADC,
Separated tip/tilt mirrors,
Dual DM design,
Integrated science instruments,
Visible and near-IR.
Coupling, all
ADC within WFS (SAXO, MagAO)
Dual DM architecture (PALM-3000)
Integrated science instruments (all)
Visible andnear-IR operation (All)

26. The future in astronomy can be separated into,
3. Future developments
The 1st generation of astronomical HOAO for 8m-class telescope is now facility-class.
The future in astronomy can be separated into,
HOAO for extremely large telescopes (ELTs),
HOAO for solar adaptive optics (Solar AO),
HOAO for space missions.

27. 3. HOAO for Extremely Large Telescopes
3 ELT-class telescopes,
Thirty Meter Telescope (Hawai’i, or La Palma*)
Giant Magellan Telescope (Chile)
European Southern Observatory ELT (Chile)
There is no planned first-generation HOAO instrument capability for the visible/near-IR
* As of September 2017 the final location is still undecided.

28. 3. Thirty Metre Telescope
NFIRAOS
1st generation
MCAO system: 2 DMs, 6 LGS and 800 Hz sampling,
equivalent to sampling of r0 per layer
Strehl is 0.5(1um).

29. 3. ESO ELT
METIS,
Post-1st generation but funded: HOAO in mid-IR.
HARMONI
1st generation with a SCAO high-resolution mode
How good is HARMONI SCAO?

30. 3. Next-generation Solar telescopes
Two major projects,
Daniel K Inouye Solar Telescope (Hawai’i)
European Solar Telescope (Tenerife)
Both have MCAO as part of their design
Can operate in SCAO-only mode
Only latter truly offers a HOAO capability but both have high spatial resolution correction.
Small r0 (~5cm) and low t0 (~0.5ms) imply even more demanding technical requirements
Fortunately, the sun is a bright source!

31. 3. Summary
The first generation of ELT instruments are all AO-enabled and a few have near HOAO quality,
The second generation of HOAO are XAO, for direct exoplanet imaging.
Solar AO is maturing into HOAO, and for the DKIST and EST it is a necessary technology.

32. The Durham HOAO instrument,
4. CHOUGH
The Durham HOAO instrument,
CANARY Hosted Upgrade for HOAO
An on-sky technology demonstrator for advanced AO concepts.

33. Technical demonstrator,
4. Design limitations
Technical demonstrator,
Throughput not important,
Size of telescope (4m) is small,
No XAO requirement,
No science drivers,
but,
Limited funding, manpower and parts…
…so we use existing equipment where possible and,
Limited telescope time ⇒ laboratory use.

34. Solution to limitations,
4. Design solutions
Solution to limitations,
Upgrade an existing AO system,
Use existing components, especially 1020 actuator DM
Make it laboratory compatible
Upgrade, (SCEXAO)
Existing components (Palm 3k)
Lab compatible (all systems)

35. 4. CANARY
Wide field-of-view, LGS-enabled, MOAO-enabled experiment for AO research
Offers,
Volume for installing CHOUGH,
An acquisition camera & off-sky test facility,
RTC computer,
Low-order DM (241 actuators),
Tip/tilt mirror,
CHOUGH uses a minority of CANARY’s abilities,
U.Durham/Paris Obs. collaboration
CANARY could be reduced to a DM relay & support equip.

36. 4. CANARY Phase C2 3x Off-axis WFSs 241-actuator DM Tip/tilt mirror
4x LGS WFSs
On-axis WFS
Infra-red path
52-actuator DM
Test sources
Acquisition camera

37. 4. CANARY → CHOUGH CHOUGH Periscope 241-actuator DM Tip/tilt mirror
Test sources
Acquisition camera

38. 4. CHOUGH 3D model
NFSI
HOWFS
KDM
Backbone
ADC
Periscope

39. 4. CHOUGH in the laboratory
CAWS
NFSI
Illuminator
HOWFS
KDM
ADC
Backbone

40. CHOUGH ADC
Prisms
Rotation stage

41. CHOUGH KDM
Kilo DM
Relay optics, Backbone

42. CHOUGH HOWFS
EMCCD
camera
Relay optics
Microlens array
Relay optics

43. CHOUGH NFSI
NIR camera
Filter wheel
Focus lens
Mirror

44. Spatial
filter
Grating
4-f reimager

45. CHOUGH performance estimates

46. 4. Summary CHOUGH is a low-cost, fast, technical HOAO experiment
In the laboratory, it can operate standalone,
On sky, it is installed into CANARY,
It is undergoing sub-system performance evaluation and final laboratory integration.

47. CONCLUSION HOAO is a specialized type of AO
Traditionally narrow-field (~1 arcsec) but new instruments increase performance at the red-end to wider fields (~1 arcmin),
High-resolution with S≥0.5, can reach S≥0.9 (XAO),
Existing facility instruments are XAO-like
Future instruments, for ELTs and Solar AO are more flexible in target brightness
More general science, and integral to the telescope design
Durham has a HOAO experiment, CHOUGH.

48. THANK YOU