Impact of Resolution in Multi-Conjugate Adaptive Optics Systems Using Segmented Mirrors (Preprint)
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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In moderate-to-strong scintillation, multi-conjugate adaptive optics MCAO appears promising to compensate for amplitude and phase fluctuations. In this research, a MCAO system is simulated with a segmented deformable mirror DM reshaping the amplitude and the second DM continuous flattening the phase after propagation from the segmented mirror. A Gerchberg-Saxton GS type algorithm is used with Fresnel propagation between DM planes. The effects of varying the phases apparent resolution on a segmented DM in the pupil plane is investigated. Results show the mean square error in the reshaped beam decreases as Dro and Rytov number increase over the range of conditions tested ro 011 m - 036 m. The field-estimated Strehl ratio drops precipitously when the number of subapertures is increased beyond about 36 across, using a branch-point- tolerant unwrapper, due to the presence of branch points. On the second DM, by using the mean of the phase within each subaperture before back propagating to the first DM plane inside the GS loop, the Strehl ratio was improved 6 - 11 percent using 4 - 19 actuators across. Further a novel method of cascading segmented DMs, of increasingly higher resolution, doing amplitude reshaping followed by a continuous DM to flatten the phase is explored.