Highcontrast AO for imaging extrasolar planets formerly known as Extreme AO

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High-contrast AO for imaging extrasolar
planets(formerly known as Extreme AO)

• Bruce Macintosh (LLNL)

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Outline

• Science motivation for Extreme AO Imaging
  extrasolar planets
• Fourier optics with perfect wavefronts
  coronagraphs
• Fourier optics with phase errors High-contrast
  AO PSFs
• ExAO system design the Gemini Planet Imager

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Formation history is encoded in distributions
Core acceretion migration predictions (IdaLin
2004)
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Orbital scattering in 3 body systemsChatterjee
et al. astro-ph/0703166
50 AU
5 AU
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Disk fragmentation efficient at 10-20 AU
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Doppler
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Direct detection spectroscopy of brown dwarfs
Mclean et al 2003
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GDPS
Lafrienere et al 2007 (Gemini Planet Survey) etc.
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Uncertainty in luminosity of young planets
Previous models
Current AO surveys
Extreme AO regime
Low-entropy core accretion models
Marley et al 2006 astro-ph/0609739
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Voyager family portrait
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Conventional AO limited by scattered light
Strehl ratio S
Halo intensity 1-S
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Extreme AO (ExAO) gain gt S/(1-S)
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High-contrast AO PSF

• Fraunhoffer regime focal plane and pupil plane
  are connected by Fourier transforms
• (x,y) pupil plane coordinates
• Natural coordinate system is in units of
  telescope diameter
• xxm/D
• (h,x) focal plane coordinates
• Natural coordinate system is in units of l/D
• h qX/(l/D)
• Spatial frequency 1/a ltgt angular scale l/a
• Upper case / lower case fourier transform pairs
• Upper case for pupil plane
• e(h,x) FTE (x,y)
• P,p PSF (intensity)

E
FT
e
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Pupil electric field from aperture and phase
Focal plane
Pupil plane
E(x,y)
e (x,h)
A aperture F phase a,f fourier transforms
of above
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Simple case uniform phase
Focal plane
Pupil plane
E(x,y)
e (x,h)
A
a2
A aperture F phase a,f fourier transforms
of above
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For small phase errors Taylor expansion
(Sivaramakrishnan et al 2002, Perrin et al 2003)
Focal plane
Pupil plane
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PSF expansion
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PSF terms

• Diffraction pattern term

Airy pattern
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aaFT(A)2 is the diffraction term
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Two-d Airy patterns
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Coronagraphs

• Invented by Bernard Lyot in 1930 for studying the
  corona of the sun without waiting for an eclipse

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How can we control diffraction?
PSFaaFT(A)2
A
PSF
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Coronagraph 1 Gaussian apodization
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Coronagraph 101 Blackman or Kaiser apodization

• A0.42-0.05 cos2p(r0.5) 0.08 cos4p(r0.5)
• More complex functions can have higher contrast
  or better throughput
• Apodizers in general are hard (impossible) to
  manufacture

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Apodization in 2d
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Shaped-pupil coronagraphs (Kasdin et al. 2003)
Pupil
PSF
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Lyot coronagraph (Lyot, 1933)
Starlight
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Lyot coronagraph (Lyot, 1933)
Planet
Sivaramakrishnan et al 2001 has a nice 1-d
analysis of how this works
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Many new coronagraphs in recent years

• Explosion of coronagraph concepts in recent years
• Lyot family
• Basic Lyot 1939 MNRAS 99, 538 Sivaramakrishnan
  et al 2001
• Band-limited Kuchner Traub 2003
• Apodized Soummer 2005 Ap.J. 618, L161
• Apodizers
• Shaped-pupil Kasdin et al 2003, Kasdin et al
  2005 Applied Optics 44 1177, etc.
• Phase-induced apodizer Guyon et al 2005 Ap.J.
  622, 744
• Interference / wave-optics
• 4-quadrant phase mask Rouan et al 2000 PASP 777
  1479
• Nulling interferometer/coronagraphs Mennesson et
  al. 2004 Proc. SPIE 4860, 32
• Optical vortices, many others
• Most practical coronagraphs only work at gt 3-5
  l/D
• Control of phase errors has been neglected

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PSF terms

• Diffraction pattern term

• Pinned speckle term
• Antisymmetric
• Traces the diffraction pattern vanishes when
  diffraction is negligible
• See Bloemhof 2003, Perrin et al 2003

• Halo term
• f2 (power spectrum of F)
• Symmetric
• Dominant source of scattered light in
  high-contrast AO!

• Strehl term
• Removes power from PSF core

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d
l/d
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White noise
White noise
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AO architecture and terms
Atmosphere parameters Coherence length r0 Wind
velocity v
WFS conjugate to DM primary
DM conjugate to telescope primary
Deformable Mirror
d
dactuator spacing
D primary mirror diameter
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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Power spectrum
Spatial frequency
Spatial frequency
Phase
Spatial frequency
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AO architecture and terms
Atmosphere parameters Coherence length r0 Wind
velocity v
WFS conjugate to DM primary
DM conjugate to telescope primary
Deformable Mirror
d
dactuator spacing
D primary mirror diameter
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Phase
Power spectra
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Phase
Power spectra
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Band-limiting for anti-aliasing spatial filter
PSF intensity
Position (arcsec)
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Spatial filter (Poyneer and Macintosh 2004)
implementation
Focal stop spatial filter l/d0.9
Science CameraCoronagraph
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Phase
Power spectra
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Random intensity of all the Fourier components
produces speckles
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(ExAO PSF movie goes here)
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As speckles average out (tD/vwind)planets can
be detected
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AO architecture and terms
Atmosphere parameters Coherence length r0 Wind
velocity v
WFS conjugate to DM primary
DM conjugate to telescope primary
Deformable Mirror
d
dactuator spacing
D primary mirror diameter
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ExAO 0 nm static errors, 5 MJ/500 MYr planet, 15
minute integration
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ExAO 1 nm static errors, 5 MJ/500 MYr planet, 15
minute integration
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ExAO 2 nm static errors, 5 MJ/500 MYr planet, 15
minute integration
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ExAO 5 nm static errors, 5 MJ/500 MYr planet, 15
minute integration
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ExAO and the Gemini Planet Imager

• 2003 Basic ExAO feasibility study and Keck
  strawman
• 2004 Gemini Extreme AO Coronagraph Conceptual
  design begins
• 2005 CfAO team selected
• 2006 (June) Project start
• First light 2010

Team LLNL Project lead AO AMNH Coronagraph
masksdesign HIA Optomechanical
software JPL Interferometer WFS UCB Science
modeling UCLA IR spectrograph UdM Data
pipeline UCSC Final integrationtest
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AO
Entrance Window
Linear ADC
Stage
Artificial sources
Gemini f/16 focus
Woofer DM Tip/Tilt
Coronagraph
Apodizer Wheel
MEMS DM
Focal Plane Occultor Wheel
Reference arm shutter
Calibration Module
F/64 focusing ellipse
LO pickoff
Dichroic
Phasing Mirror
WFS
LOWFS
WFS PC focus
Beamsplitter
Pinhole
SF
CCD
Lenslet
Collimator
WFS collimator
Filter Wheel
Polarization modulator
Filter Wheel
IR spectrograph
Lyot wheel
IR CAL WFS
Zoom Optics
CAL-IFS PC focus
Filter Wheel
Dewar Window
HAWAII II RG
Lenslet
IR Self-calibration interferometer
Pupil viewing mirror
Prism
Pupil Camera
Polarizing beamsplitter and anti-prism
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High order high-speed AO (LLNL)
Calibration/ Alignment Unit
Superpolished optics (2 nm RMS)
GPI Window
Woofer DM

• MEMS deformable mirror

Commercial computer Fourier (predictive) control
Spatially Filtered WFS 0.7-0.9 mm
Focal stop spatial filter l/d0.9
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Apodized-pupil Lyot coronagraph (Soummer 2005)
Hard-Edged Mask
Lyot Mask
Apodizer
Soummer 2005
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Integral field spectrograph (James Larkin, UCLA)
Spectrograph
Collimator Optics
Camera Optics
Detector
Prism
Lenslet Array
R.I. Telephoto Camera
Collimated light from Coronagraph
Pupil Plane
Filters
Focal Plane
Low spectral resolution (R50) High spatial
resolution (0.014 arcsec) Wide field of view (3x3
arcsec) Minimal scattered light
Lenslet
Window
Rotating Cold Pupil Stop
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Spectrograph format

• Each spectrum is 16 pixels long, one of YJHK,
  Dl/l50
• 68,000 spectra on a 2048x2048 detector 4.5
  pixel spacing
• 2.8 x 2.8 arcsecond field of view, 0.014
  arcsecond pixels

Single Spectrum
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Broad-band ExAO snapshot
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ExAO spectral data cube
James Larkin, UCLA
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Marois et al. 2006, Spie
Fresnel optics effects (more complicated than
simple Fraunhoffer model) cause speckles from
aberrations near focus not to subtract as well
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GPI mechanical design
Gemini Cassegrain support structure
GPI enclosure
Gort
Optics structure
Electronics
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GPI optical structure
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VLT Planetfinder SPHERE
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Monte Carlo models of science performance(Graham
Macintosh)
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Monte Carlo models of science performance(Graham
Macintosh)
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ExAO can detect a significant population of
planets
GPI detections
Radial velocity detections
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Extrasolar planets
H8-11 mag
H5-8 mag
H4-6 mag
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Space AO Terrestrial Planet Finder

• Terrestrial Planet Finder Coronagraph (was 2020,
  now deferred)
• Original baseline 8x3m mirror with advanced AO
  to correct internal errors
• Coronagraph works at 4 l/D -gt 0.08 arcseconds for
  8-m telescope
• Earth at 10 pc 0.1 arcsec
• Various interim 2-4 m class missions proposed
  with more advanced coronagraphs
• 2-3 l/D coronagraph allows smaller telescope
• Some visible-light spectroscopy of Earthlike
  planets

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Extrasolar planets
H8-11 mag
H5-8 mag
H4-6 mag
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Extrasolar planets
H8-11 mag
H5-8 mag
H4-6 mag
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A very large coronagraph
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TPF Occultor (Webster Cash et al)
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References

• Angel, R, Ground based imaging of extrasolar
  planets using adaptive optics, 1994 Nature 368,
  203 (Original exoplanet paper)
• Burrows, A., et al., A nongray theory of
  extrasolar planets and brown dwarfs, 1997 Ap.J
  491, 856 (Planet models)
• Sivaramakrishnan, A., et al., Ground-based
  coronagraphy with High-Order Adaptive optics,
  2001 Ap.J. 552, 397 (Lyot coronagraphs)
• Kasdin, N.J., et al, 2003, Extrasolar planet
  finding via optimized apodized pupil and shaped
  pupil coronagraphs, Ap.J. 582, 1147
• Kuchner, M, and Traub, W., A Coronagraph with a
  Band-limited Mask for Finding Terrestrial
  Planets 2002 Ap.J. 570, 200 (improved Lyot
  coronagraph)
• Sivaramakrishnan, A., et al, Speckle
  decorrelation and dynamic range in speckle noise
  limited imaging, 2002 Ap.J. 581, L59 (2nd-order
  PSF expansion)
• Perrin, M., et al. The structure of the High
  Strehl Ratio Point-Spread Functions, 2003, Ap.J.
  596, 702 (high-order PSF expansion)
• Poyneer, L, and Macintosh, B., Spatially-filtered
  wavefront sensor for high-order adaptive
  optics, 2004, JOSA A 21, 810 (aliasing WFS)
• Guyon, O., et al. Theoretical Limits on
  Extrasolar Terrestrial Planet Detection with
  Coronagraphs, 2006 Ap.J.S. 167, 81
• Cash, W., et al, The New Worlds Observer using
  occulters to directly observe planets, 2006
  Proc. SPIE 2625