Numerical Simulation On Wavefront Sensorless Correction For Laser Propagation In The Atmosphere

Compared with the traditional adaptive optical(AO)technique,wavefront sensorless adaptive optics(WFSless AO)can reduce the wavefront sensing and reconstructing process,which simplifies the system structure and broadens the potential applications areas where wavefront cannot be measured or a lightweight system structure is required.In this dissertation,the convergency rate,stability and realization flexiability of the typical optimization algorithms is compared and relative applications for laser propagation in the turbulent atmosphere is researched by theoretical analysis and numerical simulation.The main works and innovations are summaried as follows:1.Two kind of,non-deterministic model-free and deterministic model-based,optimization control algorithms principle and their design strategy for WFSless AO system are deduced and researched in theory.Algorithm convergence rate and stability of three mainly algorithms,the stochastic parallel gradient descent(SPGD)algorithm,the model-based method algorithm based on the "sphere packing" principle,and the general model-based algorithm using the linear relationship between the mean square of the aberration gradient and the second moment of the image intensity distribution,are compared and discussed in detail by numerical simulation,which provides us some significant experience for further research.2.Aiming at the characteristic of the model-based optimization algorithm which achieves a good correction effect after one correction,the concept of "fast and stable convergence ratio" is defined to evaluate the convergence properties of the model-based optimization algorithm and according to the aberration distribution of wavefront distortion caused by atmospheric turbulence,the vectorized slope factor is proposed.The results show that the vectorized slope has stronger correction effect when turbulence strengh is deep.Further,Aiming at two main problems,the difficulty of model selection and the fitting error of deformation mirror,which were found in the process of the Zemike polynomial-based general model-based optimization algorithm in WFSless AO system correction process,the general model-based algorithm using the deformation eigen mode is investigated,it is shown that the number of modes is equal to the number of actuator of the deformable mirror so that it is not necessary to redefine the correction order for different turbulence strength and can make full use of the correction ability of the deformable mirror.3.The close-loop correction system for laser propagation in the turbulent atmosphere based on a beacon light and WFSless AO system algorithms is established.The usage of optimization algorithms in the closed-loop correction system is redefined,and the convergence characteristic of two algorithm,SPGD and the general model-based algorithm,is compared and analysed using the 4D simulation platform under different algorithm iterative frequency and different turbulence situation.The results show that the general model-based algorithm,as a determistic algorithm,has a great advantage in real-time wavefront aberration correction for laser propagation in the turbulent atmosphere.4.The application of WFSless AO system based on SPGD algorithm and the return wave signal of a spatial extended non-coorporation target for the adaptive focusing of collimated laser atmospheric transmission is studied.By using a special designed laser projection system,the backfeed loop for WFSless AO system is established between the detector signal and the intensity distribution at the target,the results show that the system can use the return wave signal of spatial extended non-cooperative target to enhance the energy concentration on the target surface for collimated laser atmospheric transmission.