The Fantastical World of Adaptive Optics - EPN Campus · 2013-08-12 · ESI 2011 – Adaptive...
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The Fantastical World of The Fantastical World of Adaptive OpticsAdaptive Optics
A multimedia presentation of the physics andtechnology of adaptive optics
James W. BeleticSenior Director, Astronomy & Civil Space
2ESI 2011 – Adaptive Optics
400 Years of the Telescope
Galileo Galilei (1564–1642)
1609 - First astronomical use of the telescope
~2 cm diameter aperture
PonteVecchioPonte
Vecchio
UffiziUffizi
MuseoGalileoMuseoGalileo
PalazzoVecchioPalazzoVecchio
Firenze, Italia
3ESI 2011 – Adaptive Optics
400 Years of the TelescopeWe have come a long way…….ESO 8-meter telescope
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5ESI 2011 – Adaptive Optics
400 Years of the Telescope2009 - 17 telescopes with 6.5-meter aperture or larger
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400 Years of the Telescope2009 - 17 telescopes with 6.5-meter aperture or larger
Keck – two 10-mKeck – two 10-m
Subaru 8.2-mSubaru 8.2-m Gemini 8-mGemini 8-m
LBT – twin 8.4-mLBT – twin 8.4-m
MMT 6.5-mMMT 6.5-m
Carnegie Magellan – two 6.5-mCarnegie Magellan – two 6.5-m
Gemini 8-mGemini 8-m
HET 9.2-m (effective)HET 9.2-m (effective) Grantecan 10.4-mGrantecan 10.4-m
SALT 10-m (eff.)SALT 10-m (eff.)
ESO VLT – four 8.2-mESO VLT – four 8.2-m
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The Electromagnetic Spectrum
8ESI 2011 – Adaptive Optics
400 Years of the TelescopeThe era of the Extremely Large Telescopes (ELTs) is imminent
E-ELT42-m
1385 m2
TMT30-m
707 m2
Existing Large Telescopes
944 m2 ofcollecting area
3 6.5-m9 8-m5 10-m
GMT24.5-m359 m2
9ESI 2011 – Adaptive Optics
Why bigger telescopes ?
Light collection area = π r2See fainter objects
λ = wavelength of lightD = diameter of telescope aperturer = radius of telescope aperture = D / 2
Angular resolution = 1.22 λ / DResolve finer detail
13 milliarcsecis the apparent size ofa football in Moscowas seen from Madrid
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Understanding the performance of optical telescopes
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Introduction to Fourier Opticsby Joseph W. Goodman
(3rd edition 2005, first published in 1968)
Interferometric Imaging in Astronomyby Francois Roddier
(Physics Reports, 1988)(Vol. 170, No. 2, pp. 97-166)
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Propagation of Light
Only need the electric field to
understand telescope optics
13ESI 2011 – Adaptive Optics
Wave modelof image formation
Shui Kwok’s animation
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Phasor Representation of EM Wave
+▬ Electric Field
Direction ofPropagation
Increasing phaseIncreasing time
0° phase180°(π radians)
••
ω = 2πff = frequency
15ESI 2011 – Adaptive Optics
Huygens-Fresnel Principle of Wave Propagation
Christiaan Huygens(1629–1695)
Augustin-Jean Fresnel(1788–1827)
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OpticalAxis
ImagePlane
Diffraction-Limited Resolution
•
17ESI 2011 – Adaptive Optics
•
Diffraction-Limit
Phasor Distribution E-field Amplitude
D
•λ / DIntensity
(Amplitude2)
•2 λ / D
ESI 2009 – Adaptive Optics – James Beletic
E-field Amplitude
Diffraction-Limited ResolutionSquare
Aperture
First zero at λ / D
CircularAperture
First zero at 1.22 λ / D
Airy Diffraction Pattern
Sir GeorgeBiddell Airy
(1801–1892)
Intensity&
EncircledEnergy
Intensity
Zeroes of function
First zero, diffraction limit
1.00
0.75
0.50
0.25
0.00
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Strehl RatioMeasure 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 sourcecompared to the theoretical maximum peak intensity of a perfect imaging system working at the diffraction limit.
20ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Square Aperture - no distortionsWavefront (rms = 0 wave) Point Spread
Function
Strehl = 1.27relative to circular aperture
Only DC power
21ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - no distortionsWavefront (rms = 0 wave) Point Spread
Function
Strehl = 1.00
Only DC power
SPECSPEC Mirror 1Mirror 1 Mirror 2Mirror 2 Mirror 3Mirror 3 Mirror 4Mirror 4
R. curvature (mm)R. curvature (mm) 28800+28800+--100100 28762.928762.9 28760.028760.0 28762.628762.6 28759.228759.2WFE RMS (nm)WFE RMS (nm) N/AN/A 4242 3939 3535 1717θθ RMS (arc secs)RMS (arc secs) N/AN/A 0.0800.080 0.0740.074 0.0870.087 0.0620.062CIR @ rCIR @ r00=500mm=500mm >0.82(*)>0.82(*) 0.8750.875 0.8980.898 0.8930.893 0.9750.975CIR @ rCIR @ r00=250mm=250mm N/AN/A 0.9350.935 0.9510.951 0.9350.935 0.9810.981StrehlStrehl >0.25(*)>0.25(*) 0.7620.762 0.7910.791 0.8240.824 0.9530.953(*) (*) λλ=500 nm=500 nm
-- Very high spatial frequency errors ~3Very high spatial frequency errors ~3--7 nm RMS (wavefront)7 nm RMS (wavefront)-- Microroughness < 20 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
23ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV= 0.4 wave, rms = 0.05 wave) Point Spread
Function
Strehl = 0.91
Equal power atall spatial frequencies
24ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 0.81 wave, rms = 0.10 wave) Point Spread
Function
Strehl = 0.67
Equal power atall spatial frequencies
25ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 1.21 waves, rms = 0.15 wave) Point Spread
Function
Strehl = 0.41
Equal power atall spatial frequencies
26ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 1.61 waves, rms = 0.20 wave) Point Spread
Function
Strehl = 0.21
Equal power atall spatial frequencies
27ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 2.01 waves, rms = 0.25 wave) Point Spread
Function
Strehl = 0.09
Equal power atall spatial frequencies
28ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 2.42 waves, rms = 0.30 wave) Point Spread
Function
Strehl = 0.03
Equal power atall spatial frequencies
29ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 2.82 waves, rms = 0.35 wave) Point Spread
Function
Strehl = 0.01
Equal power atall spatial frequencies
30ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 3.22 waves, rms = 0.40 wave) Point Spread
Function
Strehl = 0.00
Equal power atall spatial frequencies
31ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - white noiseWavefront (PV = 3.63 waves, rms = 0.45 wave) Point Spread
Function
Strehl = 0.00
Equal power atall spatial frequencies
32ESI 2011 – Adaptive Optics
Mirror 4Mirror 4
WFE RMS (nm)WFE RMS (nm) 1717StrehlStrehl 0.9530.953(*) (*) λλ=500 nm=500 nm
ESO VLT 8.2-m telescope
Point SpreadFunction
Strehl = 0.91
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Atmospheric BlurringThe bane of ground-based astronomy
Long exposure imageis called the “seeing disk”
Long exposure imageBinary star pair 100 Her, 14 arc sec separation (Vmag = 6.0)
10 msec frame time
34ESI 2011 – Adaptive Optics
Resolution of Ground-based telescopes
Isaac Newton (1643–1727)
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 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
35ESI 2011 – Adaptive Optics
Long exposureimage
the “seeing disk”
Short exposureimage
(1/100 sec)
ESO Paranal ObservatorySeeing statistics for 1999-2004
Atmospheric Seeing
Full Width Half Maximum (arc sec) 0.5 µm, zenith
36ESI 2011 – Adaptive Optics
The Devilbehind
atmosphericdistortions
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 refraction
• Index of refraction of air ~ 1.0003
Atmospheric distortions are due to temperature fluctuations
• Refractivity of air
where P = pressure in millibars, T = temp. in K, n = index of refraction. VERY weak dependence on λ
• Temperature fluctuations cause index fluctuations
Pressure is constant, because velocities are highly sub-sonic -- pressure differences are rapidly smoothed out by sound wave propagation.
N ≡ (n −1) ×106 = 77.6 1+ 7.5210−3 λ −2( )× (P /T)
δN = −77.6 × (P / T 2 )δT
Important things to rememberabout the index of refraction (n) formula
• Wavefront shape (x,y,z) is the same in visible and IRCan 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 nDoesn’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!
40ESI 2011 – Adaptive Optics
Adaptive Optics“Takes the twinkle out of the stars”
θ = λ / D
Long exposureimage
Short exposureimage
Image with adaptive optics
θ = 1 arc sec
41ESI 2011 – Adaptive Optics
Neptune in infra-red light (1.65 microns)
Without adaptive optics With Keck AO
June 27, 1999May 24, 1999
Adaptive Optics (AO)The technology of sensing and removing atmospheric distortions
2.3
arc
sec
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Galactic Center
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Adaptive Optics in AstronomyEdited by Francois Roddier
(1999)
Adaptive Optics for Astronomical Telescopesby John W. Hardy
(1998)
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Simplified AO system diagram
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46ESI 2011 – Adaptive Optics
An example of correcting optics
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Not to scale
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49ESI 2011 – Adaptive Optics
Faint Object CameraImages before and after COSTAR repair
50ESI 2011 – Adaptive Optics
Demonstration ofatmospheric turbulence
51ESI 2011 – Adaptive Optics
Quantifying Atmospheric Distortions
- Power Spectrum- Correlation Length- Correlation time
52ESI 2011 – Adaptive Optics
Kolmogorov turbulence cartoon
Outer scale L0
ground
Inner scale l0
hνconvection
solar
hν
Wind shear
Andrei Kolmogorov (1903-1987)
53ESI 2011 – Adaptive Optics
Kolmogorov turbulence in a nutshell
- L. F. Richardson (1881-1953)
Big whorls have little whorls,which feed on their velocity.
Little whorls have smaller whorls,and so on unto viscosity.
Computer simulation of the breakup of a Kelvin-Helmholtz vortex
Kolmogorov Turbulence Spectrum
Energy(log)
Spatial Frequency (log)
κ-11/3
κ = 2π/λ
outerscale
innerscale
von Karmann spectrum(Kolmogorov + outer scale)
55ESI 2011 – Adaptive Optics
Circular Aperture – Fractal Noise
56ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - no distortionsWavefront (rms = 0.0 wave) Point Spread
Function
Strehl = 1.00
Only DC power
57ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - fractal noiseWavefront (PV = 0.23 wave, rms = 0.05 wave) Point Spread
Function
Strehl = 0.92
Power f – 11/3
58ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - fractal noiseWavefront (PV = 0.69 wave, rms = 0.15 wave) Point Spread
Function
Strehl = 0.45
Power f – 11/3
59ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - fractal noiseWavefront (PV = 1.60 waves, rms = 0.35 wave) Point Spread
Function
Strehl = 0.11
Power f – 11/3
60ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - fractal noiseWavefront (PV = 2.29 waves, rms = 0.50 wave) Point Spread
Function
Strehl = 0.07
Power f – 11/3
61ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 4.57 waves, rms = 1.01 waves) Point Spread
Function
Strehl = 0.01
Power f – 11/3
62ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 5.69 waves, rms = 1.18 waves) Point Spread
Function
Strehl = 0.02
Power f – 11/3
63ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 5.75 waves, rms = 1.10 waves) Point Spread
Function
Strehl = 0.02
Power f – 11/3
64ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 5.05 waves, rms = 1.15 waves) Point Spread
Function
Strehl = 0.02
Power f – 11/3
65ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 4.22 waves, rms = 1.01 waves) Point Spread
Function
Strehl = 0.02
Power f – 11/3
66ESI 2011 – Adaptive Optics
Quantifying Atmospheric Distortions
- Power Spectrum- Correlation Length- Correlation time
67ESI 2011 – Adaptive Optics
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
• r0 = Correlation lengththe 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,
r0 ∝ λ6/5
Δx
D(Δx)
r0
1 rad
68ESI 2011 – Adaptive Optics
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 μmwhich provides 74 cm r0 at 2.2 μm (K-band)
• Seeing is weakly dependent on wavelength, and gets a little better at longer wavelengths.
λ/r0 ∝ λ-1/5
69ESI 2011 – Adaptive Optics
Correlation time - τ0
τ 0 ∝ λ6/5
• To first order, atmospheric turbulence is frozen (Taylor hypothesis) and it “blows”past the telescope.
• τ0 = correlation time, the time it takes for the distortion to move one r0
• Determines how fast the AO system needs to run. Telescope primary
wind velocity = 30 mph= 13.4 m/sec
τ0 = 14 cm / v = 15 msec (visible)= 74 cm / v = 80 msec (K)
τ 0 ≃ r0/v
70ESI 2011 – Adaptive Optics
Wavefront Sensing
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 atmosphere is totally frozen (30 μsec through atmos). We draw one wavefront, but about 1012 wavefronts pass through telescope before atmospheric distortion changes.
72ESI 2011 – Adaptive Optics
Shack-Hartmann wavefront sensing
Flat wavefront
Subaperturefocal spots
uniformly spaced
Distorted wavefront
Subaperturefocal spots
unevenly spaced
73ESI 2011 – Adaptive Optics
• Divide primary mirror into “subapertures” of diameter r0
• Number of subapertures ~ (D / r0)2 where r0 is evaluated at the desired observing wavelength
• Example: Keck telescope, D=10m, r0 ~ 60 cm at λ = 2 μm. (D / r0)2 ~ 280. Actual # for Keck : ~250.
Shack-Hartmannwavefront sensing
74ESI 2011 – Adaptive Optics
Curvature wavefront sensing
75ESI 2011 – Adaptive Optics
Curvature wavefront sensing
76ESI 2011 – Adaptive Optics
Wavefront sensing
• Several ways to sense the wavefront.• Three basic things must be done:
Divide the wavefront into subaperturesOptically process the wavefrontDetect 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 wavefrontDefined by optical processing
77ESI 2011 – Adaptive Optics
Wavefront sensor family tree
Divide intosubapertures
OpticalProcessing
1st
Step
012
012
Shack-Hartmann Pyramid, Shearing
Curvature
Point source diffractionDerivativeof
measure
Shack-Hartmann wavefront sensing stands alone as to howit is implemented. Will it be the dominant wavefrontsensing method in 10 years time?
78ESI 2011 – Adaptive Optics
Deformable Mirrors
79ESI 2011 – Adaptive Optics
• 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
Piezoelectric Transducer (PZT) Mirroror Stack-Array Mirror (SAM)
80ESI 2011 – Adaptive Optics
Most deformable mirrors today have thin glass face-sheets
Reflective coating
Glass face-sheet
PZT or PMN actuators: get longer and shorter as voltage is changed
Cables leading to mirror’s power supply (where
voltage is applied)
Light
81ESI 2011 – Adaptive Optics
Deformable mirrors - many sizes
• 13 to >900 actuators (degrees of freedom)
Xinetics~5 cm
~30 cm
82ESI 2011 – Adaptive Optics
Bent / torsion principlePros:
• 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 WFSRadial or hexagonal geometry
Bimorph (or curvature) Mirror
83ESI 2011 – Adaptive Optics
Adaptive Optics Works!
84ESI 2011 – Adaptive Optics
85ESI 2011 – Adaptive Optics
Neptune without Adaptive Optics
86ESI 2011 – Adaptive Optics
Neptune with Adaptive Optics
87ESI 2011 – Adaptive Optics
Imaging the galactic center
88ESI 2011 – Adaptive Optics
89ESI 2011 – Adaptive Optics
Mass of black hole atcenter of the Milky Way
4.1±0.6 million solar masses
Andrea Ghez (UCLA)
90ESI 2011 – Adaptive Optics
Reinhard Genzel Max-Planck-Institut für
extraterrestrische Physik
Flare at galactic center
Last cries of matter fallinginto the black hole?
Test ofGeneral Relativity?
91ESI 2011 – Adaptive Optics
U.S. Air Force 3.5-meter adaptive optics systems
3.5 meter telescopesCollapsible dome
30 subapertures across pupil690 controlled subapertures
>1 kHz update rate
3.5 meter telescopesCollapsible dome
30 subapertures across pupil690 controlled subapertures
>1 kHz update rate
AEOSMaui, Hawai’i
AEOSMaui, Hawai’i
Starfire Optical RangeAlbuquerque, New Mexico
Starfire Optical RangeAlbuquerque, New Mexico
92ESI 2011 – Adaptive Optics
SeaSat Imaged with Starfire AO System
• 3.5 meter telescope• 30 subapertures across pupil• 690 controlled subapertures• 740-840 nm wavelength
• 3.5 meter telescope• 30 subapertures across pupil• 690 controlled subapertures• 740-840 nm wavelength 3 arc sec
93ESI 2011 – Adaptive Optics
The Large Binocular Telescope (LBT)Two 8.4-meter mirrors, north of Tucson, Arizona
94ESI 2011 – Adaptive Optics
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•Position control of the mirror surface• 911mm diameter• 1.6mm thick shell• 672 actuators• Settling time < 1ms• 30nm WFE
95ESI 2011 – Adaptive Optics
0.16 arc sec separation
Triple Star
The LBT AO System installed in 2010Is now being commissioned
96ESI 2011 – Adaptive Optics
Measuring AO performance
Inte
nsity
x
Definition of “Strehl”:Ratio of peak intensity to that
of “perfect” optical system
Strehl ratio
• 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
Strehl ≈ exp (-σ2)σ = mean-square
wavefront error
97ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - no distortionsWavefront (rms = 0.0 wave) Point Spread
Function
Strehl = 1.00
Only DC power
98ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Circular Aperture - atmospheric distortionWavefront (PV = 4.57 waves, rms = 1.01 wave) Point Spread
Function
Strehl = 0.01
Power f – 11/3
99ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Wavefront (PV = 2.20 waves, rms = 0.32 wave) Point SpreadFunction
Strehl = 0.04
Circular Aperture - adaptive optics, 3x3 subapertures
Power = power (fc)freq < fc
Power f – 11/3
freq > fc
fc
100ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Wavefront (PV = 1.60 waves, rms = 0.24 wave) Point SpreadFunction
Strehl = 0.13
Circular Aperture - adaptive optics, 5x5 subapertures
Power = power (fc)freq < fc
Power f – 11/3
freq > fc
fc
101ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Wavefront (PV = 1.23 waves, rms = 0.19 wave) Point SpreadFunction
Strehl = 0.29
Circular Aperture - adaptive optics, 7x7 subapertures
Power = power (fc)freq < fc
Power f – 11/3
freq > fc
fc
102ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Wavefront (PV = 0.93 wave, rms = 0.13 wave) Point SpreadFunction
Strehl = 0.55
Circular Aperture - adaptive optics, 10x10 subapertures
Power = power (fc)freq < fc
Power f – 11/3
freq > fc
fc
103ESI 2011 – Adaptive Optics
Power Spectrumof Wavefront Surface
Spatial frequency (cycles/m)
OPD Histogram with phase wrapping-λ 0 +λ
OPD Histogram-3λ 0 +3λ
+2λ
-2λ
OPD
Power
Wavefront (PV = 0.43 wave, rms = 0.06 wave) Point SpreadFunction
Strehl = 0.90
Circular Aperture - adaptive optics, 26x26 subapertures
Power = power (fc)freq < fc
Power f – 11/3
freq > fc
fc
104ESI 2011 – Adaptive Optics
AO Systems work well but not perfectly
Without AOFWHM 0.34 arc sec
Strehl = 0.6%
With AO FWHM 0.039 arc secStrehl = 34%
A 9th magnitude starImaged H band (1.6 μm)
105ESI 2011 – Adaptive Optics
Biggest limit to AO performance is noise of the wavefront measurement
106ESI 2011 – Adaptive Optics
Most important AOperformance plot
Stre
hl
Guide star magnitude
Lower order system
Higher order system
Better WFSdetectors
Factor of 2.51 per stellar magnitude2.515 = 100
107ESI 2011 – Adaptive Optics
• 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
Isoplanatism
108ESI 2011 – Adaptive Optics
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%
• θ0 depends on distribution of turbulence and conjugate of the deformable mirror.
Telescope primary
θ0 ≃ r0 / h
h
109ESI 2011 – Adaptive Optics
Turbulence arises in several placesstratosphere
Heat sources within dome
boundary layer
~ 1 km
tropopause10-12 km
wind flow around dome
110ESI 2011 – Adaptive Optics
Vertical profile of turbulence
Measured from a balloon rising through atmospheric layers
111ESI 2011 – Adaptive Optics
• Composite J, H, K band image, 30 second exposure in each band
• Field of view is 40”x40” (at 0.04 arc sec/pixel)• On-axis K-band Strehl ~ 40%, falling to 25% at
field corner
Anisoplanatism (Palomar AO system)
credit: R. Dekany, Caltech
Simulation provided by Francois Rigaut
112ESI 2011 – Adaptive Optics
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
113ESI 2011 – Adaptive Optics
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 !
114ESI 2011 – Adaptive Optics
Overcoming the limited sky coverage (few %)
provided by natural guide stars
Laser guide stars
115ESI 2011 – Adaptive Optics
The atmospheric sodium layer: altitude ~ 95 km , thickness ~ 10 km
• 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
Credit: Clemesha, 1997
Credit: Milonni, LANL
116ESI 2011 – Adaptive Optics
ESO Laser Guide Star System
117ESI 2011 – Adaptive Optics
Multi-conjugate adaptive optics
(1) Provides wider field of view(2) Increases sky coverage with
natural guide stars
Overcoming limitations to the corrected field of view
118ESI 2011 – Adaptive OpticsCourtesy: F.Rigaut
119ESI 2011 – Adaptive Optics
Omega Centauri - Multi-Conjugate Adaptive Optics
120ESI 2011 – Adaptive Optics
Gemini South 8-meter Multiple Laser Guide Star System1st Light in January 2011
121ESI 2011 – Adaptive Optics
Highest resolution Earth based image of Jupiter (from ground or space)
122ESI 2011 – Adaptive Optics
Credits Many thanks to all who contributed materials and conversations to develop this talk:Many thanks to all who contributed materials and conversations to develop this talk:
• Thomas Craven-Bartle– Flatfrog Technologies, Sweden
• Francois Rigaut– Gemini Observatory, Chile
• Paola Amico– European Southern Observatory (ESO), Chile
• Philippe Dierickx– ESO, Germany
• Enrico Marchetti– ESO, Germany
• Claire Max– Center for Adaptive Optics, UC Santa Cruz, USA
• Craig Mackay– University of Cambridge, England
• Andrea Ghez– UCLA
• Reinhard Genzel– Max-Planck-Institut für extraterrestrische Physik
• Simone Esposito– Arcetri Observatory
• Robert Fugate– Starfire Optical Range (retired)
• Thomas Craven-Bartle– Flatfrog Technologies, Sweden
• Francois Rigaut– Gemini Observatory, Chile
• Paola Amico– European Southern Observatory (ESO), Chile
• Philippe Dierickx– ESO, Germany
• Enrico Marchetti– ESO, Germany
• Claire Max– Center for Adaptive Optics, UC Santa Cruz, USA
• Craig Mackay– University of Cambridge, England
• Andrea Ghez– UCLA
• Reinhard Genzel– Max-Planck-Institut für extraterrestrische Physik
• Simone Esposito– Arcetri Observatory
• Robert Fugate– Starfire Optical Range (retired)