Optimal Control Adaptive Optics System For Solid-state Slab Lasers

Lasers are characterized by high brightness,directionality and coherence.Since the demonstration of the world's first laser in 1960,it has received extensive attentions,and has been gradually applied to many fields such as scientific research,industry,and medical treatment.the solid-state slab laser is one of the most promising architecture for high-power lasers for small size,light weight and high conversion efficiency.high output power and good beam quality are always pursued.However,with the improvement of laser output power,the edge effect,scintillation and other problems appear in solid-state slab lasers,resulting in non-linear deteriorations in r beam qualities.An adaptive optics system can effectively compensate for the wavefront distortions of the laser beam.However,the correction capability of the adaptive optics system is limited by size and cost.When the wavefront distortions exceeds the correction capability of the adaptive optics system,the direct slope reconstruction method based on the least-squares algorithm cannot obtain the optimal solution of the system.In this thesis,the following researches are carried out to address such problem.Firstly,an in-depth investigation was made about beam clean-up of the high-power solid-state slab laser using adaptive optics.the characteristics of the wavefront distortions of high-power solid-state slab lasers were systematically analyzed,and the mathematical model of the wavefront distortions was established.The problems and shortcomings of the least squares reconstruction method are discussed when the wavefront distortions exceed the correction capability of the adaptive optics system.Secondly,in order to overcome the problem of spot scintillation in the solid-state slab laser,we proposed a weighted least-squares reconstruction algorithm with slope scintillation suppression.In this method,high frequency slope scintillations are suppressed to improve the stability and accuracy of adaptive optics systems.an experimental study was carried out using a 24.6k W solid-state slab laser,after correction using the proposed method,the beam quality was improved to 1.5 times diffraction limit,at the same time,the jitters in the beam was mitigated.Then,in order to solve the problem about large phase gradients caused by edge effect in the solid-state slab laser,a least-squares wavefront reconstruction algorithm with performance-based filtering is proposed.In this method,a filter matrix was introduced to filter out the slope information of the aberrations which exceed the correction capability of adaptive optics system.After processing,the influence of uncorrectable large aberrations on adaptive optics correction is reduced,so that the small aberration can be corrected furtherly.Simulations and experiments with a 20 k W solid-state slab laser show that,compared with the least-squares wavefront reconstruction algorithm,the proposed method can effectively improve laser beam quality when wavefront distortions exceed the correction capability of adaptive optics system.Finally,an adaptive optics correction method based on the optimal solution of the system is proposed to further improve the beam quality.Numerical optimization algorithms are employed to find the surface shape of deformable mirrors to achieve the optimal beam qualities and the residual wavefront.Then the Shack-Hartmann wavefront sensor is calibrated by the residual wavefront so that the deformable mirror could generate the above surface shape controlled by the standard lease-squares reconstruction method.We verified this approach through simulations and experiments in a solid-state slab laser beam clean-up platform.The correction results show that the proposed method can improve the beam quality further compared to traditional adaptive optics system and least-squares wavefront reconstruction algorithm with performancebased filtering when the aberrations are beyond the capabilities of the deformable mirror.The work of the thesis verifies the proposed adaptive optics correction method for solid-state slab laser from theoretical analysis,simulation and experimental.It provides a feasible way for the optimization and improvement of the adaptive optics system.