First Laboratory Demonstration of AntiHalo Apodization AHA: A coronagraph afterburner

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First Laboratory Demonstration ofAnti-Halo
Apodization (AHA) A coronagraph afterburner

• Johanan L. Codona

Steward ObservatoryUniversity of Arizona
Tucson, AZ, USA
JPL/TPF Coronagraph Workshop Sept. 28-29,
2006 Pasadena, CA
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Scope of this work

• We are developing new focal-plane wavefront
  sensing techniques that can drive active halo
  suppression devices.
• We have demonstrated interferometric measurement
  of the complex halo using a Focal Plane
  Interferometer (FPI).
• We have used this focal plane information with a
  Pupil DM (PDM) to suppress the halo in closed
  loop.
• We have now also built an AHA antihalo modulator
  and used it to suppress a coronagraphic halo.

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Focal Plane Interferometer FPI

• Uses discarded starlight
• Core forms reference beam to probe halo.
• Halo processed as usual.
• Must capture both 0O and 180O phases for photon
  efficiency.
• Gives an estimate of the halo phase from minimum
  number of photons.
• Allows measurement of halo phase in presence of
  bright incoherent background by using a much
  brighter reference beam.

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FPI in Action
Intensity Pattern
Complex Halo
Airy Pattern (with DM print-through diffraction
artifacts)
Speckle Halo (phase and amplitude screen in pupil
plane)
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Using the FPI to drive a Pupil DM (PDM)

• Using a simple speckle-steering algorithm, we
  used the FPI complex amplitude measurements to
  suppress the halo in closed loop.

Intensity Halo
Halo Phase re core
When fully suppressed, phase will become
completely random. This simple system could have
gone another 1-1.5 decades fainter.
Suppressed 90O sector
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Using the FPI to drive a Pupil DM (PDM)
180O ROI
90O ROI
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Anti-Halo Apodization for 360 degree suppression
- AHA

• Use AHA complex spatial light modulator to
  directly imprint a detailed anti-halo which
  interferes destructively with the star's halo

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AHA Operation with FPI
Real FPI Data used to model the effect of AHA
Average over DM Actuator size
Example Halo
Complex Halo (FPI)
Compute DM displacements
HaloAntiHalo
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Complex Antihalo Control
Complex AntiHalo values addressable by prototype
AHA modulator
FPI Measured Complex Halo (?3)
Complex Halo Distribution

• Halo intensity suppression proportional to local
  density of points.
• Overall scale set with ND filter.
• 0.1 radian permits 100x improvement in halo
  intensity.

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Effect of AHA Illumination
AHA Modulator too bright
Antihalo level set by an ND filter setting the
fraction of core starlight used by the AHA
modulator.
AHA Modulator just right
AHA Modulator too faint
AHA Modulator too faint
Antihalo density is lowerCan't suppress halo as
far.
AHA can't suppress these speckles
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Basic FPI/PDM/AHA Lab Design

• Three beams
• Halo and Reference paths same as in FPI design.
• AHA path uses part of core starlight to feed two
  DMs in a Michelson to give complete complex field
  control.
• Uses segmented BMC 140-element MEMS DMs.
• Driven with IrisAO SmartDriver high-resolution
  electronics
• Linux-based control system.

Halo Path
DM3.3
Lyot Stop 2.2
Beam Dump
Spatial Filter
Pupil3.3
Reference Path
AHA Modulator
Spatial Filter
Detector
Laser
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AHA Operation with a 12x12 modulator
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First AHA Lab Results
Halo (unset) Anti-halo
Test Halo
DM Settings
AHA in Action Suppressed test rectangle
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First AHA Lab Results
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Comments

• AHA Works!
• Combined with an FPI, AHA should provide 2-3
  decades of improved halo suppression for any
  coronagraph design.
• Antihalo level set using ND filter, not super
  accurate control.
• 0.1 radian phase control gives 100x additional
  halo suppression from any starting point.
• Works better with smaller pixels (actuators).
• Works over entire focal plane (with larger DMs).