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The Beat-Down Phenomenon in Adaptive Optics

The Beat-Down Phenomenon in Adaptive Optics. Amir Give’on Department of Mechanical and Aerospace Engineering, Princeton University Adviser: N.J. Kasdin Jan 2004. Ever wondered why phase conjugation does not work?. Amir Give’on

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The Beat-Down Phenomenon in Adaptive Optics

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  1. The Beat-Down Phenomenonin Adaptive Optics Amir Give’on Department of Mechanical and Aerospace Engineering, Princeton University Adviser: N.J. Kasdin Jan 2004

  2. Ever wondered why phase conjugation does not work? Amir Give’on Department of Mechanical and Aerospace Engineering, Princeton University Adviser: N.J. Kasdin Jan 2004

  3. 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

  4. Problem: Given an estimate of the wavefront and a realistic DM model, what should be the DM’s shape that will create the most optimal contrast in the image plane?

  5. Ideal System

  6. Aberrated System I

  7. Aberrated System II beat-down beat-down

  8. Aberrated System III Measured aberration: Corrected image:

  9. Suppose we measure the phase aberration up to some maximum spatial frequency: We may also decompose,

  10. The components are given by the inner product: And with a bit of manipulations…

  11. 10 min later… where,

  12. Optimal Correction The corrected image is given by, The exponential term could be written as,

  13. While the cost function minimized in conventional phase conjugation is: The cost function we are going to minimize now will be:

  14. Phase aberration

  15. Point Spread Function

  16. Conventional phase conjugation

  17. Point Spread Function (corrected)

  18. Components (conventional)

  19. Components (optimal)

  20. Point Spread Function (corrected)

  21. Answer: The shape that will minimize the mean square sum of the components in the series for the exponential term.

  22. Ideal DM

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