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

Abstract

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 (diffractionignorant) geometric MCAO proportional gains as linear open-loop control parameters. In the case of Kolmogorov turbulence, expressions involving the Rytov variance and/or weighted C n 2 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.