Correctability limitations imposed by spherical-wave scintillation in multi-conjugate adaptive optics

Spherical-wave scintillation is shown to impose multi-conjugate adaptive optics (MCAO) correctability limitations that are independent of wavefront sensing and reconstruction. Residual phase and log-amplitude variances induced by scintillation in weak turbulence are derived using (diffraction-based) diffractive MCAO spatial filters or (diffraction-ignorant) geometric MCAO proportional gains as linear open-loop control parameters. In the case of Kolmogorov turbulence, expressions involving the Rytov variance and/or weighted Cn2 integrals apply. Differences in performance between diffractive MCAO and geometric MCAO resemble chromatic errors. Optimal corrections based on least squares imply irreducible performance limits that are validated by wave-optic simulations.

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