Performance of the self referencing interferometer in the presence of simulated deep turbulence and noise effects

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Authors
Johnson, Lee T.
Subjects
Adaptive optics
self-referencing interferometer
spatial light modulator
deep turbulence
Advisors
Agrawal, Brij N.
Kim, Jae-Jun
Date of Issue
2013-12
Date
Dec-13
Publisher
Monterey, California: Naval Postgraduate School
Language
Abstract
Current laser weapon systems are limited to close range encounters because the laser beam attenuates quickly within the atmosphere. A phenomenon known as deep turbulence is characterized by strong scintillation and branch points in the wave-front phase. Many wave-front sensors perform poorly in the presence of deep turbulence, and are unable to accurately reconstruct the wave-front. This paper examines a wave-front sensor, the self-referencing interferometer (SRI) that is theoretically immune to the effects of deep turbulence. The SRI is both simulated mathematically and constructed in the lab for comparison between analytical and experimental results. Performance of the SRI is analyzed in the presence of realistic deep turbulence effects generated by a spatial light modulator, and realistic noise effects introduced by the digital imaging system. Simulated results show a significant loss of signal level as turbulence is increased, but a resilience of the wave-front sensor above a signal-to-noise ratio of two. Analogously, in the experimental results the signal drops off rapidly with increasing levels of turbulence, and reaches unacceptably low levels above a Rytov number of 0.4. A qualitative analysis of the wave-front reconstruction shows remarkable similarity between simulated and experimental results, though the experimental results contain far more error induced branch points than in the simulation. Methods are being explored to boost the signal and reduce the noise at the camera to allow the system to handle higher levels of turbulence.
Type
Thesis
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Department
Mechanical and Aerospace Engineering (MAE)
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Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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