High-frequency folding and optimal phase conjugation for high-contrast adaptive optics

Conventional adaptive optics methods use phase conjugation based on measurements of the phase aberrations at the pupil plane. The measurements are typically done using a Shack-Hartmann sensor sampling at spatial frequencies determined by the spatial frequency limitations of the deformable mirror. The work presented here shows that the nulling needed for high contrast imaging cannot be achieved using such a methodology. Linear combinations of high frequencies in the aberration at the pupil plane "fold" and appear as low frequency aberrations at the image plane. We present an optimized solution for the shape of the deformable mirror based on the Fourier decomposition of the effective phase aberration.