TheThe FantasticalFantastical WorldWorld ofof AdaptiveAdaptive OpticsOptics A multimedia presentation of the physics and technology of adaptive James W. Beletic Senior Director, & Civil Space 400 Years of the 1609 - First astronomical use of the telescope

~2 cm diameter aperture

Firenze, Italia

Galileo Galilei (1564–1642) PontePonte VecchioVecchio

UffiziUffizi

MuseoMuseo PalazzoPalazzo GalileoGalileo VecchioVecchio

ESI 2011 – Adaptive Optics 2 400 Years of the Telescope We have come a long way…….ESO 8-meter telescope

ESI 2011 – Adaptive Optics 3 ESI 2011 – Adaptive Optics 4 400 Years of the Telescope 2009 - 17 with 6.5-meter aperture or larger

ESI 2011 – Adaptive Optics 5 400 Years of the Telescope 2009 - 17 telescopes with 6.5-meter aperture or larger

KeckKeck –– two two 10-m10-m

LBTLBT –– twin twin 8.4-m8.4-m HETHET 9.2-m9.2-m (effective)(effective) GrantecanGrantecan 10.4-m10.4-m

Subaru 8.2-m Subaru 8.2-m GeminiGemini 8-m8-m MMTMMT 6.5-m6.5-m

GeminiGemini 8-m8-m

SALTSALT 10-m10-m (eff.)(eff.)

ESOESO VLTVLT –– four four 8.2-m8.2-m CarnegieCarnegie MagellanMagellan –– two two 6.5-m6.5-m ESI 2011 – Adaptive Optics 6 The Electromagnetic Spectrum

ESI 2011 – Adaptive Optics 7 400 Years of the Telescope The era of the Extremely Large Telescopes (ELTs) is imminent

GMT 24.5-m TMT 359 m2 30-m 707 m2 Existing Large E-ELT Telescopes 42-m 2 944 m of 2 collecting area 1385 m 3 6.5-m 9 8-m 5 10-m

ESI 2011 – Adaptive Optics 8 Why bigger telescopes ?

See fainter objects Light collection area = π r2 Resolve finer detail = 1.22 λ / D

λ = wavelength of light D = diameter of telescope aperture r = radius of telescope aperture = D / 2

13 milliarcsec is the apparent size of a football in Moscow as seen from Madrid

ESI 2011 – Adaptive Optics 9 Understanding the performance of optical telescopes

ESI 2011 – Adaptive Optics 10 Introduction to Fourier Optics Interferometric Imaging in Astronomy by Joseph W. Goodman by Francois Roddier (3rd edition 2005, first published in 1968) (Physics Reports, 1988) (Vol. 170, No. 2, pp. 97-166)

ESI 2011 – Adaptive Optics 11 Propagation of Light

Only need the electric field to understand telescope optics

ESI 2011 – Adaptive Optics 12 Wave model of image formation

Shui Kwok’s animation

ESI 2011 – Adaptive Optics 13 Phasor Representation of EM Wave

ω = 2πf f = frequency Direction of Propagation

Increasing phase Increasing time

180° 0° phase (π radians)

▬ Electric Field +

• •

ESI 2011 – Adaptive Optics 14 Huygens-Fresnel Principle of Wave Propagation

Christiaan Huygens Augustin-Jean Fresnel (1629–1695) (1788–1827)

ESI 2011 – Adaptive Optics 15 Diffraction-Limited Resolution

Image Plane

Optical • Axis

ESI 2011 – Adaptive Optics 16 Diffraction-Limit

Phasor Distribution E-field Amplitude

D •

λ / D • Intensity E-field Amplitude (Amplitude2)

2 λ / D •

ESI 20112009 – Adaptive Optics – James Beletic 17 Diffraction-Limited Resolution

Square Circular Aperture Aperture

Airy Diffraction Pattern

Intensity

Zeroes of function

First zero, diffraction limit Sir George Biddell Airy (1801–1892)

1.00

0.75 Intensity & 0.50 Encircled Energy 0.25

0.00 First zero at λ / D First zero at 1.22 λ / D Strehl Ratio Measure of the quality of imaging system

The Strehl ratio is the ratio of the observed peak intensity at the detection plane of a telescope or other imaging system from a point source compared to the theoretical maximum peak intensity of a perfect imaging system working at the diffraction limit.

ESI 2011 – Adaptive Optics 19 Square Aperture - no distortions

Wavefront (rms = 0 wave) +2λ

OPD

-2λ

Power Only DC power

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Surface -λ 0 +λ Strehl = 1.27 OPD Histogram with phase wrapping relative to circular aperture ESI 2011 – Adaptive Optics 20 Circular Aperture - no distortions

Wavefront (rms = 0 wave) Point Spread Function +2λ

OPD

-2λ

Power Only DC power

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 1.00 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 21 SPEC 1 Mirror 2 Mirror 3 Mirror 4 R. curvature (mm) 28800+-100 28762.9 28760.0 28762.6 28759.2 WFE RMS (nm) N/A 42 39 35 17 θ RMS (arc secs) N/A 0.080 0.074 0.087 0.062

CIR @ r0=500mm >0.82(*) 0.875 0.898 0.893 0.975

CIR @ r0=250mm N/A 0.935 0.951 0.935 0.981 Strehl >0.25(*) 0.762 0.791 0.824 0.953 (*) λ=500 nm

- Very high spatial frequency errors ~3-7 nm RMS (wavefront) - Microroughness < 20 Å - Correction forces typically ~80 N (spec <120 N) - Matching error measured by direct Hartmann test, negligible (below measurement accuracy) - All radii of curvature within 3.7 mm

ESO VLT 8.2-m telescope Circular Aperture - white noise

Wavefront (PV= 0.4 wave, rms = 0.05 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.91 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 23 Circular Aperture - white noise

Wavefront (PV = 0.81 wave, rms = 0.10 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.67 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 24 Circular Aperture - white noise

Wavefront (PV = 1.21 waves, rms = 0.15 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.41 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 25 Circular Aperture - white noise

Wavefront (PV = 1.61 waves, rms = 0.20 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.21 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 26 Circular Aperture - white noise

Wavefront (PV = 2.01 waves, rms = 0.25 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.09 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 27 Circular Aperture - white noise

Wavefront (PV = 2.42 waves, rms = 0.30 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.03 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 28 Circular Aperture - white noise

Wavefront (PV = 2.82 waves, rms = 0.35 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.01 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 29 Circular Aperture - white noise

Wavefront (PV = 3.22 waves, rms = 0.40 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.00 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 30 Circular Aperture - white noise

Wavefront (PV = 3.63 waves, rms = 0.45 wave) Point Spread Function +2λ

OPD

-2λ

Power Equal power at all spatial frequencies

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.00 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 31 Point Spread Function

Mirror 4 WFE RMS (nm) 17 Strehl 0.953 (*) λ=500 nm

ESO VLT 8.2-m telescope Strehl = 0.91

ESI 2011 – Adaptive Optics 32 Atmospheric Blurring The bane of ground-based astronomy

Long exposure image is called the “seeing disk”

Long exposure image Binary star pair 100 Her, 14 arc sec separation (Vmag = 6.0) ESI 2011 – Adaptive Optics 10 msec frame time 33 Resolution of Ground-based telescopes

If the Theory of making Telescopes could at length be fully brought in Practice, yet there would be certain Bounds beyond which Telescopes could not perform. For the Air through which we look upon the Stars, is in a perpetual Tremor; as may be seen by the tremulous Motion of Shadows cast from high Towers, and by the twinkling of the fix’d Stars…

And all these illuminated Points constitute one broad lucid Point, composed of those many trembling Points confusedly and insensibly mixed with one another by very short and swift Tremors, and thereby cause Isaac Newton (1643 1727) – the Star to appear broader than it is…

The only Remedy is a most serene and quiet Air, such as may perhaps be found on the tops of the highest Mountains above the grosser Clouds. Isaac Newton, Opticks, 1704

ESI 2011 – Adaptive Optics 34 Atmospheric Seeing

ESO Paranal Observatory Seeing statistics for 1999-2004

Long exposure image the “seeing disk”

Short exposure image (1/100 sec) Full Width Half Maximum (arc sec) 0.5 µm, zenith

ESI 2011 – Adaptive Optics 35 The Devil behind atmospheric distortions

ESI 2011 – Adaptive Optics 36 Velocity of light

• Velocity v of light through any medium v = c / n

c = speed of light in a vacuum (3.28×108m/s) n = index of

• Index of refraction of air ~ 1.0003 Atmospheric distortions are due to temperature fluctuations • Refractivity of air N ≡ (n −1) ×106 = 77.6 (1+ 7.5210−3 λ −2)× (P /T) where P = pressure in millibars, T = temp. in K, n = index of refraction. VERY weak dependence on λ • Temperature fluctuations cause index fluctuations δN = −77.6 × (P / T 2 )δT Pressure is constant, because velocities are highly sub- sonic -- pressure differences are rapidly smoothed out by sound wave propagation. Important things to remember about the index of refraction (n) formula

• Wavefront shape (x,y,z) is the same in visible and IR Can measure in visible (lower noise detectors) and compensate for the infrared (easier to correct)

• 1 °C temp change = 1 part in a million change in n Doesn’t seem like much, eh? 1 wave distortion in 1 meter! (λ=1 μm)

• Thermal issues bite all major telescopes who don’t pay attention to thermal issues! Adaptive Optics “Takes the twinkle out of the stars”

Short exposure Long exposure Image with image image adaptive optics

θ = 1 arc sec θ = λ / D

ESI 2011 – Adaptive Optics 40 Adaptive Optics (AO) The technology of sensing and removing atmospheric distortions in infra-red light (1.65 microns) Without adaptive optics With Keck AO 2.3 arc sec

May 24, 1999 June 27, 1999

ESI 2011 – Adaptive Optics 41 Galactic Center

ESI 2011 – Adaptive Optics 42 Adaptive Optics in Astronomy Adaptive Optics for Astronomical Telescopes Edited by Francois Roddier by John W. Hardy (1999) (1998)

ESI 2011 – Adaptive Optics 43 Simplified AO system diagram

ESI 2011 – Adaptive Optics 44 ESI 2011 – Adaptive Optics 45 An example of correcting optics

ESI 2011 – Adaptive Optics 46 Not to scale

ESI 2011 – Adaptive Optics 47 ESI 2011 – Adaptive Optics 48 Faint Object Camera Images before and after COSTAR repair

ESI 2011 – Adaptive Optics 49 Demonstration of atmospheric turbulence

ESI 2011 – Adaptive Optics 50 Quantifying Atmospheric Distortions

- Power Spectrum - Correlation Length - Correlation time

ESI 2011 – Adaptive Optics 51 Andrei Kolmogorov (1903-1987) Kolmogorov turbulence cartoon

solar Outer scale L0 Inner scale l0

hν

Wind shear

convection hν

ground

ESI 2011 – Adaptive Optics 52 Kolmogorov turbulence in a nutshell

Big whorls have little whorls, which feed on their velocity. Little whorls have smaller whorls, and so on unto viscosity.

- L. F. Richardson (1881-1953)

Computer simulation of the breakup of a Kelvin-Helmholtz vortex

ESI 2011 – Adaptive Optics 53 Kolmogorov Turbulence Spectrum

von Karmann spectrum (Kolmogorov + outer scale) κ = 2π/λ Energy (log) κ-11/3

outer inner scale scale

Spatial Frequency (log) Circular Aperture – Fractal Noise

ESI 2011 – Adaptive Optics 55 Circular Aperture - no distortions

Wavefront (rms = 0.0 wave) Point Spread Function +2λ

OPD

-2λ

Power Only DC power

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 1.00 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 56 Circular Aperture - fractal noise

Wavefront (PV = 0.23 wave, rms = 0.05 wave) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.92 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 57 Circular Aperture - fractal noise

Wavefront (PV = 0.69 wave, rms = 0.15 wave) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.45 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 58 Circular Aperture - fractal noise

Wavefront (PV = 1.60 waves, rms = 0.35 wave) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.11 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 59 Circular Aperture - fractal noise

Wavefront (PV = 2.29 waves, rms = 0.50 wave) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.07 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 60 Circular Aperture - atmospheric distortion

Wavefront (PV = 4.57 waves, rms = 1.01 waves) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.01 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 61 Circular Aperture - atmospheric distortion

Wavefront (PV = 5.69 waves, rms = 1.18 waves) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.02 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 62 Circular Aperture - atmospheric distortion

Wavefront (PV = 5.75 waves, rms = 1.10 waves) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.02 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 63 Circular Aperture - atmospheric distortion

Wavefront (PV = 5.05 waves, rms = 1.15 waves) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.02 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 64 Circular Aperture - atmospheric distortion

Wavefront (PV = 4.22 waves, rms = 1.01 waves) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.02 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 65 Quantifying Atmospheric Distortions

- Power Spectrum - Correlation Length - Correlation time

ESI 2011 – Adaptive Optics 66 Correlation length - r0 • Fractal structure (self-similar at all scales) • Structure function (good for describing random functions) D(Δx) = [phase(x) – phase(x+Δx)]2 D(Δx) 1 rad •r = Correlation length r 0 0 Δx the distance Δx where D(Δx) = 1 rad2

•r0 = max size telescope that is diffraction-limited •r0 is wavelength dependent – larger at longer wavelengths (since 1 radian is bigger for larger λ) • But a little tricky, 6/5 r0 ∝λ

ESI 2011 – Adaptive Optics 67 Correlation length - r0

• Rule of thumb: 10 cm visible r0 is 1 arc sec seeing • Visible r0 is usually quoted at 0.55 μm.

0.7 arc sec seeing is 14 cm r0 at 0.55 μm which provides 74 cm r0 at 2.2 μm (K-band)

• Seeing is weakly dependent on wavelength, and gets a little better at longer wavelengths.

-1/5 λ/r0 ∝λ

ESI 2011 – Adaptive Optics 68 Correlation time - τ0 • To first order, atmospheric turbulence is frozen (Taylor hypothesis) and it “blows” past the telescope. • τ = correlation time, wind velocity = 30 mph 0 = 13.4 m/sec the time it takes for the τ0 = 14 cm / v = 15 msec (visible) distortion to move one r0 = 74 cm / v = 80 msec (K) 6/5 τ 0 ≃ r0/v τ 0 ∝λ • Determines how fast the AO system needs to run. Telescope primary

ESI 2011 – Adaptive Optics 69 Wavefront Sensing

ESI 2011 – Adaptive Optics 70 Misrepresentations & Misinterpretations

• All drawings are exaggerated, since need to exaggerate to show distortions & angles. Maximum phase deviation across 10-meter wavefront is about 10 μm – 1 part in 1 million. Like one dot offset on a straight line of 600 dpi printer in 165 feet (50 meters).

• From the point of view of light, the is totally frozen (30 μsec through atmos). We draw one wavefront, but about 1012 pass through telescope before atmospheric distortion changes. Shack-Hartmann wavefront sensing

Flat wavefront Subaperture focal spots uniformly spaced

Distorted wavefront Subaperture focal spots unevenly spaced

ESI 2011 – Adaptive Optics 72 Shack-Hartmann wavefront sensing

• Divide primary mirror into “subapertures” of diameter r0 2 • Number of subapertures ~ (D / r0) where r0 is evaluated at the desired observing wavelength

• Example: Keck telescope, D=10m, r0 ~ 60 cm at λ = 2μm. 2 (D / r0) ~ 280. Actual # for Keck : ~250.

ESI 2011 – Adaptive Optics 73 Curvature wavefront sensing

ESI 2011 – Adaptive Optics 74 Curvature wavefront sensing

ESI 2011 – Adaptive Optics 75 Wavefront sensing

• Several ways to sense the wavefront. • Three basic things must be done: Divide the wavefront into subapertures Optically process the wavefront Detect photons Detecting photons must be done last, but order of the first two steps can be interchanged. Can measure the phase, or 1st derivative, or 2nd derivative of the wavefront Defined by optical processing

ESI 2011 – Adaptive Optics 76 Wavefront sensor family tree

1st Divide into Optical Step subapertures Processing

Point source diffraction Derivative 0 0 of 1 Shack-Hartmann1 Pyramid, Shearing measure 2 2 Curvature

Shack-Hartmann wavefront sensing stands alone as to how it is implemented. Will it be the dominant wavefront sensing method in 10 years time?

ESI 2011 – Adaptive Optics 77 Deformable

ESI 2011 – Adaptive Optics 78 Piezoelectric Transducer (PZT) Mirror or Stack-Array Mirror (SAM)

• Push-pull principle (piezoelectric effect) • Local influence functions • Pros: • Fast (few kHz) resonance frequency • No theoretical limit for the number of actuators • Cons: •Few µm stroke • Print-through issues • ~$1k/actuator, bulky power supplies (few hundred volts) • Generally used with Shack-Hartmann WFS • Rectangular or hexagonal geometry

ESI 2011 – Adaptive Optics 79 Most deformable mirrors today have thin glass face-sheets

Glass face-sheet

Light Cables leading to mirror’s power supply (where voltage is applied)

PZT or PMN actuators: get longer and shorter Reflective coating as voltage is changed

ESI 2011 – Adaptive Optics 80 Deformable mirrors - many sizes

• 13 to >900 actuators (degrees of freedom)

~30 cm

~5 cm Xinetics

ESI 2011 – Adaptive Optics 81 Bimorph (or curvature) Mirror

Bent / torsion principle Pros: • Global influence functions • Stroke of several microns • Cheaper than PZT • Less print-through than PZT Cons: • Slower (few hundred Hz) resonance frequency • Limited to a few hundred actuators Generally used with curvature WFS Radial or hexagonal geometry

ESI 2011 – Adaptive Optics 82 Adaptive Optics Works!

ESI 2011 – Adaptive Optics 83 ESI 2011 – Adaptive Optics 84 Neptune without Adaptive Optics

ESI 2011 – Adaptive Optics 85 Neptune with Adaptive Optics

ESI 2011 – Adaptive Optics 86 Imaging the galactic center

ESI 2011 – Adaptive Optics 87 ESI 2011 – Adaptive Optics 88 Andrea Ghez (UCLA)

Mass of black hole at center of the

4.1±0.6 million solar masses

ESI 2011 – Adaptive Optics 89 Reinhard Genzel Max-Planck-Institut für extraterrestrische Physik

Flare at galactic center Last cries of matter falling into the black hole?

Test of General Relativity? ESI 2011 – Adaptive Optics 90 U.S. Air Force 3.5-meter adaptive optics systems

AEOSAEOS StarfireStarfire Optical Optical RangeRange Maui,Maui, Hawai’iHawai’i Albuquerque,Albuquerque, NewNew MexicoMexico

3.53.5 metermeter telescopestelescopes CollapsibleCollapsible domedome 3030 subaperturessubapertures acrossacross pupilpupil 690690 controlledcontrolled subaperturessubapertures >1>1 kHzkHz updateupdate raterate

ESI 2011 – Adaptive Optics 91 SeaSat Imaged with Starfire AO System

•• 3.5 3.5 metermeter telescopetelescope •• 30 30 subaperturessubapertures acrossacross pupilpupil •• 690 690 controlledcontrolled subaperturessubapertures •• 740-840 740-840 nmnm wavelengthwavelength 3 arc sec

ESI 2011 – Adaptive Optics 92 The Large Binocular Telescope (LBT) Two 8.4-meter mirrors, north of Tucson, Arizona

ESI 2011 – Adaptive Optics 93 The LBT adaptive secondary mirror

LBT672a unit: • 911mm diameter • 1.6mm thick shell, (Mirror lab) • 672 actuators • Settling time < 1ms • 30nm WFE

Main advantages: •No extra surfaces ••Position911mm control diameter of the mirror surface• 1.6mm thick shell • 672 actuators • Settling time < 1ms • 30nm WFE

ESI 2011 – Adaptive Optics 94 The LBT AO System installed in 2010 Is now being commissioned

0.16 arc sec separation

Triple Star

ESI 2011 – Adaptive Optics 95 Measuring AO performance

Strehl ratio

Definition of “Strehl”: Ratio of peak intensity to that of “perfect” optical system

Strehl ≈ exp (-σ2) σ = mean-square

wavefront errorIntensity x • When AO system performs well, more energy in core • When AO system is stressed (poor seeing), halo contains

larger fraction of energy (diameter ~ λ/r0) • Ratio between core and halo varies during night

ESI 2011 – Adaptive Optics 96 Circular Aperture - no distortions

Wavefront (rms = 0.0 wave) Point Spread Function +2λ

OPD

-2λ

Power Only DC power

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 1.00 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 97 Circular Aperture - atmospheric distortion

Wavefront (PV = 4.57 waves, rms = 1.01 wave) Point Spread Function +2λ

OPD

-2λ

–11/3 Power Power f

-3λ 0 +3λ OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.01 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 98 Circular Aperture - adaptive optics, 3x3 subapertures

Wavefront (PV = 2.20 waves, rms = 0.32 wave) Point Spread Function +2λ

OPD

-2λ

Power = power (fc) freq < f Power c Power f –11/3

freq > fc

-3λ 0 +3λ fc OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.04 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 99 Circular Aperture - adaptive optics, 5x5 subapertures

Wavefront (PV = 1.60 waves, rms = 0.24 wave) Point Spread Function +2λ

OPD

-2λ

Power = power (fc) freq < f Power c Power f –11/3

freq > fc

-3λ 0 +3λ fc OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.13 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 100 Circular Aperture - adaptive optics, 7x7 subapertures

Wavefront (PV = 1.23 waves, rms = 0.19 wave) Point Spread Function +2λ

OPD

-2λ

Power = power (fc) freq < f Power c Power f –11/3

freq > fc

-3λ 0 +3λ fc OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.29 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 101 Circular Aperture - adaptive optics, 10x10 subapertures

Wavefront (PV = 0.93 wave, rms = 0.13 wave) Point Spread Function +2λ

OPD

-2λ

Power = power (fc) freq < f Power c Power f –11/3

freq > fc

-3λ 0 +3λ fc OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.55 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 102 Circular Aperture - adaptive optics, 26x26 subapertures

Wavefront (PV = 0.43 wave, rms = 0.06 wave) Point Spread Function +2λ

OPD

-2λ

Power = power (fc) freq < f Power c Power f –11/3

freq > fc

-3λ 0 +3λ fc OPD Histogram

Spatial frequency (cycles/m)

Power Spectrum of Wavefront Surface -λ 0 +λ Strehl = 0.90 OPD Histogram with phase wrapping ESI 2011 – Adaptive Optics 103 AO Systems work well but not perfectly

A 9th magnitude star Imaged H band (1.6 μm)

Without AO With AO FWHM 0.039 arc sec FWHM 0.34 arc sec Strehl = 34% Strehl = 0.6% ESI 2011 – Adaptive Optics 104 Biggest limit to AO performance is noise of the wavefront measurement

ESI 2011 – Adaptive Optics 105 Most important AO performance plot

Higher order system Strehl

Lower order system

Factor of 2.51 per stellar magnitude 2.515 = 100

Better WFS detectors

Guide star magnitude ESI 2011 – Adaptive Optics 106 Isoplanatism

• The core of the globular cluster M15. • The brightest stars are about 13 mag, and the faintest visible in each frame are about 16 mag. • Frame time is 80 msec, and the frame is 20 x 20 arc sec

ESI 2011 – Adaptive Optics 107 Anisoplanatism - θ0 • An object that is not in same direction as the guide star (used for AO system) has a different distortion.

• θ0 = isoplanatic angle, the angle over which the max. Strehl drops by 50% h

θ0 ≃ r0 / h

• θ0 depends on distribution of turbulence and conjugate Telescope primary of the .

ESI 2011 – Adaptive Optics 108 Turbulence arises in several places

stratosphere tropopause 10-12 km

wind flow around dome boundary layer ~ 1 km Heat sources within dome

ESI 2011 – Adaptive Optics 109 Vertical profile of turbulence

Measured from a balloon rising through atmospheric layers ESI 2011 – Adaptive Optics 110 Anisoplanatism (Palomar AO system)

credit: R. Dekany, Caltech

• Composite J, H, K band image, 30 second exposure in each band • Field of view is 40”x40” (at 0.04 arc sec/pixel) Simulation provided • On-axis K-band Strehl ~ 40%, falling to 25% at by Francois Rigaut field corner

ESI 2011 – Adaptive Optics 111 Combination of: - Brightness required for guide star - Isoplanatic angle - Distribution of “bright” stars on the sky Only few % of the sky is accessible with natural guide star AO

ESI 2011 – Adaptive Optics 112 Two choices for addressing limited sky coverage

(1) Find science “under the lamp post” (i.e. live within natural constraints)

(2) Make your own guide star !

ESI 2011 – Adaptive Optics 113 Overcoming the limited sky coverage (few %) provided by natural guide stars

Laser guide stars

ESI 2011 – Adaptive Optics 114 The atmospheric sodium layer: altitude ~ 95 km , thickness ~ 10 km

Credit: Clemesha, 1997

Credit: Milonni, LANL

• Layer of neutral sodium atoms in mesosphere (height ~ 95 km) • Thought to be deposited as smallest meteorites burn up • Total of about 200 kg around entire Earth

ESI 2011 – Adaptive Optics 115 ESO Guide Star System

ESI 2011 – Adaptive Optics 116 Overcoming limitations to the corrected field of view

Multi-conjugate adaptive optics

(1) Provides wider field of view (2) Increases sky coverage with natural guide stars

ESI 2011 – Adaptive Optics 117 Courtesy: F.Rigaut ESI 2011 – Adaptive Optics 118 Omega Centauri - Multi-Conjugate Adaptive Optics

ESI 2011 – Adaptive Optics 119 Gemini South 8-meter Multiple System 1st Light in January 2011

ESI 2011 – Adaptive Optics 120 Highest resolution Earth based image of Jupiter (from ground or space)

ESI 2011 – Adaptive Optics 121 ManyMany thanksthanks toto allall whowho contributedcontributed materialsmaterials Credits andand conversationsconversations toto developdevelop thisthis talk:talk:

•• Thomas Thomas Craven-BartleCraven-Bartle –– Flatfrog Flatfrog Technologies,Technologies, SwedenSweden •• Francois Francois RigautRigaut –– Gemini ,Observatory, ChileChile •• Paola Paola AmicoAmico –– European European SouthernSouthern ObservatoryObservatory (ESO),(ESO), ChileChile •• Philippe Philippe DierickxDierickx –– ESO, ESO, GermanyGermany •• Enrico Enrico MarchettiMarchetti –– ESO, ESO, GermanyGermany •• Claire Claire MaxMax –– Center Center forfor AdaptiveAdaptive OptiOptics,cs, UCUC SantaSanta Cruz,Cruz, USAUSA •• Craig Craig MackayMackay –– University University ofof Cambridge,Cambridge, EnglandEngland •• Andrea Andrea GhezGhez –UCLA–UCLA •• Reinhard Reinhard Genzel Genzel –– Max-Planck-Institut Max-Planck-Institut fürfür extraterrestrischeextraterrestrische PhysikPhysik •• Simone Simone EspositoEsposito –– Arcetri Arcetri ObservatoryObservatory •• Robert Robert FugateFugate –– Starfire Starfire Optical Optical RangeRange (retired)(retired) ESI 2011 – Adaptive Optics 122