Research On Beam Jitter Control Technology In Adaptive Optics Systems

Adaptive optics(AO)is a real-time correction system for wavefront distortions.It is widely equipped in astronomical telescopes for obtaining the diffraction-limited images and high power laser systems for high beam qualities.However,as the complexity of AO systems increasing,beam jitter has become a limiting factor for future improving the performance of the systems.Therefore,this paper focuses on the problem of beam jitter in adaptive optics systems:1.Firstly,the second-order autoregressive model is chosen to describe the beam jitter according to the analysis about the originations.Based on the beam jitter model,the non-linear least squares fitting method named Levenberg-Marquardt is adapted to acquire the model parameters.So,Levenberg-Marquardt optimization method is proposed to fit the power spectral density curve of the beam jitter signal for obtaining the meaningful physical model parameters,namely the damping coefficient K and the oscillation source power?~2.With the beam jitter model identified,it is natural to establish the accurate description of the beam jitter in adaptive optics systems.2.Secondly,the local integral method is presented to smooth and then segment the power spectral density curve for extracting single-frequency beam jitter components from the multiple-frequency beam jitter signal.In order to acquire the accurate model of multiple-frequency beam jitter signal,Levenberg-Marquardt optimization method is run successively according to the segmentation.It is beneficial for the processing and the analysis of the beam jitter caused by different system components in adaptive optics.3.Thirdly,based on the model identification,linear quadratic Gaussian(LQG)control which is optimal control strategy with respect to the minimum residual variance is established according to the beam jitter control system.The coefficients of the controller are computed by fitting the corresponding power spectral density curve using Levenberg-Marquardt optimization method.The results of the simulations indicate that with the model identified,LQG control can mitigate different frequency beam jitter ranging from wide low-frequency vibration to high-frequency vibration peaks.Also,compared with an integrator,LQG control exhibits a significant improvement for beam jitter control.Besides,the possibility of the online identification and control is also discussed here.4.Finally,LQG control based on identification for the mitigation of different frequency beam jitter has been accomplished in laboratory.The experimental results verify that the proposed control technology can not only attenuate the beam jitter caused by atmospheric turbulence or platform disturbance,but also effectively suppress the vibrations introduced by various system components.Above all,based on the research on the beam jitter control,it is available to mitigate different frequency beam jitter,which is superior for improving the performance of adaptive optics systems.At the same time,the effective implementation of LQG control based identification solves the problem that high-frequency vibration peaks are difficult to be suppressed in common adaptive optics systems.