The BeatDown Phenomenon in Adaptive Optics

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The Beat-Down Phenomenonin Adaptive Optics

• Amir Giveon
• Department of Mechanical and Aerospace
  Engineering, Princeton University
• Adviser N.J. Kasdin
• Jan 2004

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Ever wondered why phase conjugation does not work?

• Amir Giveon
• Department of Mechanical and Aerospace
  Engineering, Princeton University
• Adviser N.J. Kasdin
• Jan 2004

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Princeton TPF project (space-based )

• Contrast ratio needed 1010
• Aberrations do not change over time
• The main source of aberrations is the optical
  components in the system
• Very long integration time

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Problem
Given an estimate of the wavefront and a
realistic DM model, what should be the DMs shape
that will create the most optimal contrast in the
image plane?
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Ideal System
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Aberrated System I
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Aberrated System II
beat-down
beat-down
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Aberrated System III
Measured aberration
Corrected image
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Suppose we measure the phase aberration up to
some maximum spatial frequency
We may also decompose,
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The components are given by the inner product
And with a bit of manipulations
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(No Transcript)
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10 min later
where,
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Optimal Correction
The corrected image is given by,
The exponential term could be written as,
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While the cost function minimized in conventional
phase conjugation is
The cost function we are going to minimize now
will be
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Phase aberration
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Point Spread Function
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Conventional phase conjugation
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Point Spread Function (corrected)
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Components (conventional)
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Components (optimal)
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Point Spread Function (corrected)
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Answer
The shape that will minimize the mean square sum
of the components in the series for the
exponential term.
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Ideal DM