Optimization Of Wavefront Reconstruction And Wavefront Control In Adaptive Optics Systems

With the development of large-diameter optical astronomical telescopes, thenumbers of actuators and subapertures in adaptive optics (AO) systems keepgrowing, requiring the advance of wavefront reconstruction and wavefront control.Meanwhile, the appearance and development of new types of AO systems, forexample, the deformable secondary mirror AO systems, bring new challenges to thetraditional wavefront reconstruction methods. In this paper, regarding to the newrequirements of AO systems, a series of optimized wavefront reconstruction andwavefront control technologies are proposed.Firstly, based on the averaging effect of the Hadamard calibration and the sparsecharacteristics of the zonal interaction matrix, a novel multichannel-Hadamardcalibration of the interaction matrix of the AO system is proposed. Theory analysisand experiments show that the measurement precision of themultichannel-Hadamard method is higher than the Hadamard only method and themultichannel only method.Secondly, based on the turbulence induced noise rejection capability of themodulation method and the sparse characteristics of the zonal interaction matrix, anovel multichannel-modulation calibration of the interaction matrix of the AOsystem is presented. Theory analysis and experimental results show that themultichannel-modulation calibration method can effectively reject the atmosphereinduced noise as well as greatly reduce the calibration time.Thirdly, considering the misalignment between the wavefront sensor andwavefront corrector, a direct compute of the interaction matrix of the AO systemwith a Hartmann-Shack wavefront sensor is proposed. Experimental results showthat the interaction matrix measurement efficiency is greatly improved because thismethod can only need to measure the slope response of several selected actuators.Fourthly, considering the time delay in real AO systems, the relationshipbetween the closed-loop residual variances and the closed-loop-3dB bandwidths aremodified, and thus the modified effective bandwidths of the AO systems arepresented. Numerical simulation demonstrates that the modified effectivebandwidths can be used to estimate the closed-loop residual variance moreeffectively. Fifthly, based on the modified effective bandwidths, the optimal closed-loopbandwidth of the tilt-correction loop in the AO system is derived. Simulations withdifferent atmospheric turbulences and measurement noises show that the theoreticalvalues of the optimal closed-loop bandwidths agree with the simulated values.Finally, based on the self-adaption of the adaptive filter and the stability of thePI controller, a “LMSI-2” controller is proposed. Simulations show that the LMSI-2contoller can effectively reduce the closed-loop residual error as well as avoid theoscillation phenomenon during the convergence process of the adaptive filter.