Antihalo apodization for exoplanet imaging with the GMT

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Anti-halo apodization for exoplanet imaging with
the GMT
John Codona and Roger Angel Steward Observatory
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Controlling star halo is the big problem

• In reflected light, planets very close to star
• Best cases for G stars already known
• 0.1 arcsec 10-8
• Thermal detection sources not known gt 5 AU
• PSF given by Fourier transform
• Close-in speckles set by low frequency waves
• Malbet Shao
• low order control can clear region close to star

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Controlling diffraction

• Lyot coronagraph is inefficient close in
• Poor transmision
• Broadened PSF

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Speckles induced in a 1.6 micron real star image
from the MMT AO system
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GMT PSF to 10-765 in core vs 84 for filled
circular disc Deff24 m
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radial cross section through corrected region,
scaled for 1.65 microns. The PSF is less than
10-5 at 2.3 ?/D i.e. 33 mas at 1.65 microns and
0.1 arcsec at 5 ?m. Deff24 m for the GMT
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Wavefront control strategy

• Use conventional systems at optical wavelengths
  to obtain high Strehl
• Add focal plane sensor to tune up errors from
  chromatic difference, non-common path,
  diffraction residues
• Science and FP sensor should be one and the same
• Zero or low noise fast sensor in IR is critical

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Two focal plane strategies

• Create anti halo with main dm
• Create antihalo after star block
• Reform blocked light
• Add in interferometrically

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Main HCIT result is not specific to particular
suppression system - halo suppression by
controlled deformation of a deformable pupil
mirror
Quite distinct from coronagraphy. DM is
modulated so as to superpose a psf with equal
amplitude but opposite phase. Works even with no
coronagraph Works for diffraction, amplitude and
phase errors but only over half field
(antisymmetric) inherently chromatic
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New result from Codona- closed loop AO from
focal plane
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Closed loop psf shaping in Lab
AO closed loop from focal plane measurements with
coronagraphic interferometer Wavefront shaping
with 140 element Mems DM Commands from complex
amplitude of halo measured by phase shifts of
interferometer reference beam Starting point is
deliberately aberrated PSF with 70
Strehl (Codona, Angel, Putnam)
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Argand diagram showing addition of unit amplitude
phasors in the Michelson anti-halo
synthesis Ten random complex amplitudes are
each synthesized from two unit amplitude
phasors Phase angles set by displacements of
the dm actuators.
Chromatic effects in anti-halo creation