Solar Multi-conjugate Adaptive Optics For High Resolution Imaging

Nowadays multi-conjugate adaptive optics (MCAO), in whichthree-dimensional (3D) phase distortion induced by atmospheric turbulenceis sensedby making use of several guide stars, and then controls a number of DMs conjugatedinto different altitude to widen the compensated field of view by correcting the phasedistortions in situ, has become one of the most interesting researches on adaptiveoptics. For the demand of high resolution observation of solar active region, this PhD dissertation is aimed to study solar multi-conjugate adaptive optics. More attentionis paid to three-dimensional wavefront sensing of atmospheric turbulence, numericalsimulation and design of solar multi-conjugate adaptive optics system based on1-meter solar telescope.Three-dimensional wavefront sensing of atmosphere turbulence is crucial torealize multi-conjugate adaptive optics technology. In this dissertation, modaltomography, which is one of the most important algorithms for3D wavefrontsensing, is analyzed in theory, the principle limitation of modal tomography isproposed. Based on this view the tomographic error is discussed and the simulationresults for different errors are presented. The analysis results show that part Zernikemodal basis is used as a new basis of polynomial decomposition in modaltomography, which leads to modal coupling error and aliasing error. Theun-correlation of part Zernike modal basis is the prerequisite to avoid modal aliasingerror, but modal coupling error cannot be removed and we can only restrain itsinfluence. Combined with simulation result a method with large field of view (FOV)sensing and small FOV reconstruction is proposed and gives a good performance tocontrol modal coupling error.In the other field, Ground Layer Adaptive Optics (GLAO) which correctsground layer turbulence and the average algorithm for ground layer turbulenceestimate are analyzed. Power spectrum filter method is present to describe the effectof GLAO. As a special case of atmosphere tomography, average algorithm isproposed for the first time that can reconstruct atmosphere turbulence in two layers.Simulation analyzes is present for the major factors which influenced the systemcorrection effect of GLAO. The simulation result indicates that the compensate effect is related to the proportion of ground layer turbulence intensity and field ofview.Furthermore, the experimental demonstration is carried out for the performanceof atmosphere tomography and average algorithm evaluation, using sunspot andsolar granulation as the beacons. A large FOV correlation Shark-Hartmann isdesigned and employed to get turbulence aberration from several light of fieldsimultaneously. The FOV cover by its detector is some60arcsec to the side in eachof the30subapertures. We use the observation of the5off axis regions to calculatethe deformation of the wavefront of ground and high layer turbulence, and thensimulate GLAO and two layers MCAO correction in open loop, the result shows itiseffective to reconstruct the turbulence in different layers.At last, a solar multi-conjugate adaptive optics system is designed andsimulated for1meter solar telescope. This system contains two parts, including a127-element adaptive optics for correcting ground layer turbulence and a37-elementfor high layer. It shows that the two-conjugate adaptive optics can obtain obvioushigh resolution in1’ FOV, and the non-conjugated of DM and turbulence layer hasmore influence for higher turbulence layer.This dissertation is pioneering work in domestic, which is aimed to study solarMCAO and GLAO for the demand of high resolution observation of solar activeregion. It has laid a foundation for MCAO system and will help to promote thedevelopment of adaptive optics technology.