High Order Adaptive Optics A global overview and the Durham perspective Nazim Ali Bharmal n.a.bharmal@dur.ac.uk 2017/Apr/2017

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.

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.

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

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.

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

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

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,

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

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

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

1. Examples of sub-systems Low/Medium-Order DM ~200--800 actuators ~Ø0.75m Courtesy Microgate Srl Italy

1. Examples of sub-systems Low-Order DM 247 actuator DM Ø39mm Courtesy ALPAO SaS France Medium-/High-Order DM ~400--4000 actuator MEMS DM 9.2mm × 9.2mm active area Courtesy Boston Micromachines Corp. USA

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

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

1. Examples of sub-systems http://www.imaging-git.com/science/light-microscopy/quantitative-phase-microscopy Imaging & Microscopy High-resolution WFS (typical) >500 sub-apertures ← Pyramid ↓ Quadrant-cell SH University of Durham

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

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

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).

2. PALM-3000 doi:10.1088/0004-637X/776/2/130 Courtesy Astrophysical Journal, Note Palm-241 as predecessor No LGS capability

2. SCExAO Courtesy IoP doi:10.1086/682989

2. MagAO ASM Courtesy ????

2. MagAO Courtesy ????

2. SAXO, SPHERE Courtesy ????

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)

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.

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.

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).

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?

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!

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.

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

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.

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)

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.

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

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

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

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

CHOUGH ADC Prisms Rotation stage

CHOUGH KDM Kilo DM Relay optics, Backbone

CHOUGH HOWFS EMCCD camera Relay optics Microlens array Relay optics

CHOUGH NFSI NIR camera Filter wheel Focus lens Mirror

Spatial filter Grating 4-f reimager

CHOUGH performance estimates

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.

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.

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