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<p>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.
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<br>Subjects: Adaptive optics; self-referencing interferometer; spatial light modulator; deep turbulence</div>
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Johnson, Lee T.</div>
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