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arXiv · 2012.12695

Measuring Phase Errors in the Presence of Scintillation

Justin R. Crepp·Stanimir O. Letchev·Sam J. Potier·Joshua H. Follansbee·Nicholas T. Tusay
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Abstract

Strong turbulence conditions create amplitude aberrations through the effects of near-field diffraction. When integrated over long optical path lengths, amplitude aberrations (seen as scintillation) can nullify local areas in the recorded image of a coherent beam, complicating the wavefront reconstruction process. To estimate phase aberrations experienced by a telescope beam control system in the presence of strong turbulence, the wavefront sensor (WFS) of an adaptive optics must be robust to scintillation. We have designed and built a WFS, which we refer to as a "Fresnel sensor," that uses near-field diffraction to measure phase errors under moderate to strong turbulent conditions. Systematic studies of its sensitivity were performed with laboratory experiments using a point source beacon. The results were then compared to a Shack-Hartmann WFS (SHWFS). When the SHWFS experiences irradiance fade in the presence of moderate turbulence, the Fresnel WFS continues to routinely extract phase information. For a scintillation index of $S = 0.55$, we show that the Fresnel WFS offers a factor of $9\times$ gain in sensitivity over the SHWFS. We find that the Fresnel WFS is capable of operating with extremely low light levels, corresponding to a signal-to-noise ratio of only $\mbox{SNR}\approx 2-3$ per pixel. Such a device is well-suited for coherent beam propagation, laser communications, remote sensing, and applications involving long optical path-lengths, site-lines along the horizon, and faint signals.

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Justin R. Crepp, Stanimir O. Letchev, Sam J. Potier, Joshua H. Follansbee, Nicholas T. Tusay. 2020-12-22. Measuring Phase Errors in the Presence of Scintillation. https://doi.org/10.1364/oe.408825

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