Optical Propagation Effects on Wavefront Sensing and Deformable Mirror Control in Solar Multi-Conjugated Adaptive Optics

Abstract

As global infrastructure depends more on technology, vulnerability to solar activity grows. Ground-based observations provide high-resolution solar observations needed for further understanding of the Sun. However, they are hindered by atmospheric turbulence. Multi-Conjugate Adaptive Optics (MCAO) mitigates these distortions, enabling sharp imaging across wide fields. Yet implementing solar MCAO is difficult due to strong daytime turbulence and short wavelengths, which heighten scintillation and complicate control.
Firstly, this thesis proposes a method to reduce the required high altitude turbulence size with 10 nm intensity-weighted mean wavefront error, capable of reducing 55% simulation time to generate a new turbulence layer in optical communications and up to 27% for solar MCAO.
After that, this thesis seeks to enhance solar MCAO simulation speed by accelerating the Shack-Hartmann Wavefront Sensor (SH-WFS) model. The intensity-weighted gradient (IG) method is introduced as a more efficient alternative to the conventional Fourier transform (FT) method. The IG method uses simulation time only 35–60% and memory usage by 30-40% of the FT method while preserving the accuracy of 3 nm RMS error. The error of the noise equivalent angle of SH-WFS in scintillation is less than 10% of the scintillation-free.
Additionally, this thesis investigates pupil distortion in MCAO systems, identifying DM-induced scintillation and RMS actuator shifts as significant contributors to control errors. Results show system performance degrades when scintillation exceeds 0.1 or actuator shifts surpass 10% of the actuator pitch. These insights are critical for optimising MCAO systems in solar observation and other high-turbulence applications.