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Strehl Ratio Probabilities for Phase-Only Adaptive Optics
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This is a NAVAL POSTGRADUATE SCHOOL MONTEREY CA report procured by the Pentagon and made available for public release. It has been reproduced in the best form available to the Pentagon. It is not spiral-bound, but rather assembled with Velobinding in a soft, white linen cover. The Storming Media report number is A188263. The abstract provided by the Pentagon follows: Atmospheric turbulence will induce phase and amplitude fluctuations in propagating electromagnetic waves, such as a laser beam. Adaptive optical systems attempt to compensate for these distortions. The Strehl ratio is a measure of the peak, on-axis intensity after propagation through turbulence divided by the peak irradiance for vacuum propagation. This thesis investigated the probability distribution of the Strehl ratio of a perfect, phase-only, adaptive optical system as a function of the atmospheric coherence length Ro divided by the actuator spacing, d. Using an efficient Fourier algorithm and 28 workstations running in parallel, over 850 million computer simulations were performed for 25 different Ro/d ratios in order to produce a histogram of the irradiance probability distribution. The results show that the Strehl ratio follows a log-normal probability distribution even for very small probabilities. A second set of computer simulations introduced intensity scintillation by including the log-amplitude variance parameter, cu. sigma sub l. Much faster, state-of-the-art computer workstations enabled over two billion realizations on 18 machines running in parallel for comparable time periods. The trends of these results are more complex and will require further research and deeper investigation.
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