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In the studies of Fourier optics, sound synthesis, stellar interferometry, optical tweezers, and diffractive optical elements (DOEs) it is often important to know the spatial frequency phase of an observed wave source. In order to reconstruct this phase the Adaptive-Additive Algorithm (or AA algorithm), which derives from a group of adaptive (input-output) algorithms, can be used. The AA algorithm is an iterative algorithm that utilizes the Fourier Transform to calculate an unknown part of a propagating wave, normally the spatial frequency phase (k space). This can be done when given the phase’s known counterparts, usually an observed amplitude (position space) and an assumed starting amplitude (k space). To find the correct phase the algorithm uses error conversion, or the error between the desired and the theoretical intensities. The AA algorithm is currently being implemented by [http://hillslab.umd.edu/ Dr. Wendell Hill III] , Alex Robel, V. Kotlyar Soifer, and [http://physics.nyu.edu/grierlab/cgh2b/node6.html David G Grier] .

The algorithm

History

The adaptive-additive algorithm was originally created to reconstruct the spatial frequency phase of light intensity in the study of stellar interferometry. Since then, the AA algorithm has been adapted to work in the fields of Fourier Optics by Soifer and [http://hillslab.umd.edu/ Dr. Hill] , soft matter and optical tweezers by [http://physics.nyu.edu/grierlab/cgh2b/node6.html Dr. Grier] , and sound synthesis by Robel.

Pseudo-code algorithm

1. Define input amplitude and random phase 2. Forward Fourier Transform 3. Separate transformed amplitude and phase 4. Compare transformed amplitude/intensity to desired output amplitude/intensity 5. Check convergence conditions 6. Mix transformed amplitude with desired output amplitude and combine with transformed phase 7. Inverse Fourier Transform 8. Separate new amplitude and new phase 9. Combine new phase with original input amplitude 10. Loop back to Forward Fourier Transform

Example

For the problem of reconstructing the spatial frequency phase ("k"-space) for a desired intensity in the image plane ("x"-space). Assume the amplitude and the starting phase of the wave in "k"-space is a $A_0$ and $phi_n^\left\{k\right\}$ respectively. Fourier transform the wave in "k"-space to "x" space.

: $A_0e^\left\{iphi_n^\left\{k xrightarrow\left\{FFT\right\} A_n^fe^\left\{iphi_n^\left\{f$

Then compare the transformed intensity $I_n^f$ with the desired intensity $I_0^f$, where

: $I_n^f = left\left(A_n^f ight\right)^2,$

: $varepsilon = sqrt\left\{left\left(I_n^f ight\right)^2 - left\left(I_0 ight\right)^2\right\}.$

Check $varepsilon$ against the convergence requirements. If the requirements are not met then mix the transformed amplitude $A_n^f$ with desired amplitude $A^f$.

:

where "a" is mixing ratio and

: $A^f = sqrt\left\{I_0\right\}$.

"Note that "a" is a percentage, defined on the interval 0 ≤ "a" ≤ 1.

Combine mixed amplitude with the "x"-space phase and inverse Fourier transform.

:

Separate and $phi^k_n$ and combine $A_0$ with $phi^k_n$. Increase loop by one $n o n + 1$ and repeat.

Limits

*If $a = 1$ then the AA algorithm becomes the Gerchberg–Saxton algorithm.
*If $a = 0$ then .

ee also

* Gerchberg–Saxton algorithm
* Fourier optics
* Holography
* Interferometry
* Sound Synthesis

References

*citation
last=Dufresne
first=Eric
last2=Grier
first2=David G
last3=Spalding
title=Computer-Generated Holographic Optical Tweezer Arrays
journal=Review of Scientific Instruments
volume=72 | issue=3
month=December | year=2000
.
*citation
last=Grier
first=David G
date=October 10, 2000.
url=http://www.physics.nyu.edu/~dg86/cgh2b/node6.html
.
*citation
last=Robel
first=Axel
title=Adaptive Additive Modeling With Continuous Parameter Trajectories
url=http://ieeexplore.ieee.org/iel5/10376/32978/101109TSA2005858529.pdf?arnumber=101109TSA2005858529
.
*citation
last=Robel
first=Axel
place=University of Berlin Germany
publisher=Einsteinufer 17, 10587
location=Berlin, Germany.
.
*cite book
last=Soifer
first=V. Kotlyar
last2=Doskolovich,
first2=L.
title=Iterative Methods for Diffractive Optical Elements Computation
year=1997
publisher=Taylor & Francis
location=Bristol, PA
isbn=978-0748406340

* [http://staff.chess.cornell.edu/~shen/workshop2003/presentations/Talk_DiFabrizio.pdf A PDF/Power Point Presentation that describes the uses and variations of the AA algorithm] "Berkeley, Ca".
* [http://physics.nyu.edu/grierlab/cgh2b/node6.html David Grier's Lab] Presentation on optical tweezers and fabrication of AA algorithm.
* [http://www-ccrma.stanford.edu/~roebel/addsyn/index.html Adaptive Additive Synthesis for Non Stationary Sound] Dr. Axel Robel.
* [http://hillslab.umd.edu/ Hill Labs] "University of Maryland College Park".

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